OPTIMUM OVERHANG GEOMETRY FOR HIGH RISE OFFICE
BUILDING ENERGY SAVING IN TROPICAL CLIMATES
DILSHAN REMAZ OSSEN
UNIVERSITY TEKNOLOGI MALAYSIA
BAHAGIAN A – Pengesahan Kerjasama*
Adalah disahkan bahawa projek penyelidikan tesis ini telah dilaksanakan melalui
kerjasama antara _______________________ dengan _______________________
Disahkan oleh : ………………………………………………………………………
Tandatangan
: ………………………………….
Nama
: …………………………………
Tarikh :
Jawatan
: …………………………………
(Cop rasmi)
* Jika penyediaan tesis/projek melibatkan kerjasama.
.
.
BAHAGIAN B – Untuk Kegunaan Pejabat Sekolah Pengajian Siswazah
Tesis ini telah diperiksa dan diakui oleh:
Nama dan Alamat
Pemeriksa Luar :
Nama dan Alamat
Pemeriksa Dalam :
Nama Penyelia
Lain (jika ada) :
Asst. Prof. Dr. Noor Hanita Bt Abdul Majid
Kulliyyah of Architecture and
Environmental Design
International Islamic University Malaysia
JalanGombak, 53100 Kuala Lumpur
Assoc. Prof. Dr. Mohd Rashid Bin Embi
Department of Architecture
Faculty of Built Environment
Universiti Teknologi Malaysia
81310 Skudai, Johor Bahru
………………………………………………
………………………………………………
………………………………………………
………………………………………………
Disahkan oleh Penolong Pendaftar di SPS:
Tandatangan
: ……………………………………
Nama
: GANESAN A/L ANDIMUTHU
Tarikh : ……………..
OPTIMUM OVERHANG GEOMETRY FOR HIGH RISE OFFICE BUILDING
ENERGY SAVING IN TROPICAL CLIMATES
DILSHAN REMAZ OSSEN
A thesis submitted in fulfillment of the
requirements for the award of the degree of
Doctor of Philosophy
Faculty of Built Environment
Universiti Teknologi Malaysia
SEPTEMBER, 2005
ii
iii
To:
My Beloved Father, Mother and Brother
iv
ACKNOWLEDGEMENT
My deepest gratitude goes to my main thesis supervisor Assoc. Prof. Dr.
Mohd Hamdan Ahmad for his valuable and close supervision, guidance, comments,
resources, encouragement, motivation, inspirations and friendship rendered
throughout the study. I am also very thankful to my co-supervisor Assoc. Prof. Dr.
Nor Haliza Madros for her critics advice, guidance, motivation and friendship.
Without their continued support and interest, this thesis would not have been the
same as presented here.
The author wishes to acknowledge the Public Service Department, Malaysia
and the Malaysian Government for the scholarship. I also acknowledge the
Malaysia’s High Commissioner and the staff (year 2001-2002) of the Malaysian
High Commission in Sri Lanka for offering the opportunity and information
regarding the Malaysian Commonwealth Scholarship and Fellowship Plan. My
thanks also go to Mr. T. K. Azoor and the steering committee members of COSLAM
for their encouragement and support in obtaining the scholarship. I would also like to
express my gratitude to the Universiti Teknologi Malaysia and the Department of
Architecture for accepting me as one of their doctorate students.
A special thanks to Mdm. Halimah Yahya for her assistance in obtaining the
required weather data and also for her friendship and support. Many thanks also go to
Agung Murti for helping with the graphics and Roshida with the translations.
My sincere gratitude also goes to those who have provided assistance in
many ways at various occasions: Dr. R. Emmanuel from University of Moratuwa, Sri
Lanka; Prof. Dr. Najib Ibrahim, Assoc. Prof. Syed Zainol Abidin Idid and family and
Dr. Mohd. Tetsu Kubota from UTM. Thank also due to Shahzarimin and his family,
Azril and his family, Dr. M. Mukhlis, Dr. Monzurul Alam, Kamarudzaman, Syed
Hossin, Adil, Asif, Ashiq, Rumi, Jami, Kayser and Arif for their brotherhood and
friendship. I am also grateful to Tilak and family, Praveena and her family, my
cousins Suzaniya & Remano and Mr. & Mrs. Ramzan for their constant concern and
moral support.
My heartiest and utmost gratitude goes to my dear father, mother and brother
for their patience, sacrifices, understanding, constant concern, moral support and
prayers during the course of my study. Finally, I thank Almighty Allah for giving me
patience, courage, strength, mercy, guidance and blessings to face all challenges in
life and to complete this thesis successfully.
v
ABSTRACT
Intercepting the radiant heat wave using external solar shading before
penetrating to the internal environment through the envelope openings is the main
criterion to prevent solar heat gains into the building. In hot and humid climates, one
draw back of using the external shading device is the risk of reducing daylight level
in the interior space, which in turn increases the use of artificial lighting. Therefore,
it is important to understand the magnitude of energy consumption for cooling and
lighting when shading devices are adapted in order to propose optimum external
horizontal shading device strategies as design solutions in hot and humid climates.
This study investigates the effect of six different depths of external horizontal
shading device on incident solar radiation, transmitted solar heat gains, natural-light
penetration, building cooling and energy consumption. The experiment was carried
out using a standard, single fenestration perimeter office room in a typical high-rise
office building. The investigation is conducted using the eQUEST-3 dynamic energy
simulation program supported by the DOE2.2 calculation engine. The results showed
that overhang ratios of 1.2, 1.6, 0.6 and 0.8 reduced the incident direct solar radiation
more than 80% on the east, west, north and south orientations respectively. The
target illuminance of 500lux for internal lighting was obtained for overhang ratios of
1.0, 1.3, 0.2 and 1.0 on respective orientations. Further, findings indicated that
deeper natural light penetration can be achieved through the bare window under
Malaysian sky conditions compared to the common rule of thumb of 2.5 times the
window height on all orientations considered. The findings also revealed that
optimum energy savings of 14%, 11%, 6% and 8% were achieved by optimum
overhang ratios of 1.3, 1.2 and 1.0 on the east, west and north, south orientations
respectively. This study concludes, considering the trade off between total heat gain
and natural-light penetration to optimize the total energy consumption as the best
option in designing external solar shading in hot and humid climates.
vi
ABSTRAK
Pemintasan pancaran haba dari matahari menggunakan alat redupan luaran
sebelum menembusi persekitaran dalaman melalui bukaan adalah ciri-ciri utama bagi
mengelakkan pertambahan haba solar di dalam bangunan. Dalam iklim panas dan
lembap, satu kelemahan menggunakan alat redupan adalah risiko terhadap
pengurangan kadar cahaya siang yang mana boleh sebaliknya meningkatkan
penggunaan cahaya buatan pula. Oleh itu adalah penting bagi memahami magnitud
penggunaan tenaga untuk penyejukan dan pencahayaan apabila alat redupan
digunakan bagi mencadangkan strategi menggunakan alat redupan mendatar luaran
yang optimum sebagai penyelesaian rekabentuk dalam iklim panas dan lembap.
Kajian ini juga menilai kesan enam perbezaan lebar alat redupan mendatar luaran
terhadap insiden gelombang suria, penambahan transmisi kepanasan suria,
kemasukan cahaya semulajadi, penyejukan bangunan dan penggunaan tenaga.
Kajian ini dijalankan melalui simulasi fenestrasi sebuah bilik pejabat dalam
bangunan tinggi yang dianggap tipikal. Penilaian ini dikendalikan menggunakan
eQUEST – 3, satu program simulasi tenaga yang dinamik berbantukan mesin
pengiraan DOE2.2. Keputusan menunjukkan nisbah unjuran 1.2, 1.6, 0.6 dan 0.8
dapat mengurangkan penerimaan pancaran haba terus matahari lebih daripada 80%
pada arah timur, barat, utara dan selatan. Sasaran illuminasi 500lux untuk
pengcahayaan dalaman dicapai pada nisbah unjuran 1.0, 1.3, 0.2 dan 1.0 pada arah
yang sama. Seterusnya, penemuan mendapati kemasukan cahaya semulajadi melalui
tingkap yang terdedah di bawah keadaan awan Malaysia adalah lebih jauh
berbanding dengan 2.5 kali ketinggian tingkap ygmenjadi kebiasaan pada semua arah
yang diambil kira. Penemuan juga mendedahkan bahawa penjimatan tenaga yang
optima pada 14%, 11%, 65 dan 8% dapat dicapai dengan nisbah unjuran yang optima
1.3 dan 1.2 untuk 1.0 pada timur dan barat untuk utara dan selatan. Kajian ini
menyimpulkan bahawa penggunaan alat redupan dengan mengambil kira imbangan
jumlah penambahan haba dan pancaran cahaya semulajadi bagi mencapai jumlah
penggunaan tenaga yang optima adalah pilihan terbaik bagi rekabentuk redupan
luaran dalam iklim panas dan lembap.
vii
TABLE OF CONTENTS
CHAPTER
1
TITLE
PAGE
THESIS TITLE
i
DECLARATION
ii
DEDICATION
iii
ACKNOWLEDGEMENT
iv
ABSTRACT (ENGLISH)
v
ABSTRAK (BAHASA MELAYU)
vi
TABLE OF CONTENTS
vii
LIST OF TABLES
xvi
LIST OF FIGURES
xxi
LIST OF ABBREVIATIONS
xxx
LIST OF SYMBOLS
xxxiii
LIST OF APPENDIXES
xxxix
GENERAL INTRODUCTION
1.1 Introduction
1
1.2 The Problem Statement
4
1.3 Research Hypothesis
5
1.4 Research Questions
6
1.5 Research Gap
6
1.6 Research Objective
9
1.7 Scope and Limitations
10
1.8 Importance of the Research
12
viii
1.9 Thesis Organization
2
SOLAR RADIATION AND ANALYSIS OF
MALAYSIAN SKY CONDITIONS
2.1 Solar Radiation: Source of Heat and Light
17
2.2 Solar Geometry
18
2.3 Solar Distribution
19
2.3.1 Solar Intensity
20
2.3.2 Components of Solar Radiation: Direct,
Diffuse and Reflected Radiation
20
2.4 Solar Radiation Calculation
2.5
2.6
3
13
22
2.4.1 Calculation of Clear Sky Solar Radiation
23
2.4.2 Solar Radiation Calculations on Horizontal
Surfaces
24
2.4.3 Solar Radiation Calculations on Vertical
Surfaces
25
Analysis of Kuala Lumpur Sky Conditions
26
2.5.1 Sky Condition
27
2.5.2 Solar Radiation Analysis
30
2.5.3 Outdoor Design Temperature Analysis
37
2.5.4 Exterior Illuminance Analysis
40
Summary
47
ENERGY USE IN HIGH-RISE BUILDING, HEAT
GAIN AND SOLAR SHADING
3.1 Energy Consumption Pattern in Malaysia
3.1.1
Energy Consumption in Buildings
3.1.1.1 Energy Efficient Building Codes and
Standards
50
51
52
ix
3.1.2 Basic Principles of Energy Efficiency in
High-rise Buildings
54
3.1.2.1 Climate Rejecting Building
55
3.1.2.2 Climate Adapted Building
56
3.1.2.3 Combination of Climate Adapted and
Climate Rejected Building
57
3.1.3 Review Related Research on High-Rise
Office Building
59
3.1.3.1 High-rise Building Form and
Orientation
60
3.1.3.2 High-Rise Building Core
62
3.1.3.3 The Floor Plan
64
3.1.3.4 Building Envelope
66
3.1.3.5 Court Yards, Atria, Wind Scoops and
Open Corridors
68
3.2 Heat Gains
3.2.1 Modes of Heat Transfer in Buildings
69
69
3.2.1.1 Conduction
69
3.2.1.2 Convection
70
3.2.1.3 Radiation
70
3.2.2 Types of Heat Transfer in Buildings
71
3.2.2.1 Heat Transfer through Building Fabric
71
3.2.2.2 Heat Gain through Window
72
3.2.2.3 Infiltration
78
3.2.2.4 Impact of Electric Lighting
79
3.2.2.5 Occupants Heat Gains
81
3.2.2.6 Equipment Heat Gains
81
3.3 Solar Shading
82
x
3.3.1 Analysis of Types of Shading Devices
84
3.3.1.1 Orientation
84
3.3.1.2 Vegetation
85
3.3.1.3 Internal Devices
86
3.3.1.4 External Devices
88
3.3.2 Method of Designing a Shading Device
90
3.3.2.1 Shadow Angles
90
3.3.2.2 Shading Mask and Sun-Path Diagram
91
3.3.2.3 Awning Geometry
94
3.3.3 Heat Gain through Externally Shaded Window
96
3.3.4 Effectiveness of External Shading Device
98
3.3.5 Factors Affecting the Effectiveness of Shading
Device
99
3.3.5.1 Geometry of External Shading Device
99
3.3.5.2 Surface Properties and Color
103
3.3.5.3 Location of Shading Device
104
3.3.5.4 Effectiveness of Different External
Horizontal Shading Methods
105
3.3.5.5 Shading Device Optical Properties
105
3.3.6 External Shading Device and Side-lit Daylight
Concept
109
3.3.6.1 Adequate Illuminance on the Work
Surface
111
3.3.6.2 Daylight Factor and Sun Illuminance
Ratio
112
3.3.6.3 Daylight –Electric Light Integration
116
3.3.7 Research on Solar Shading
119
xi
3.3.7.1 Shading Strategies and Solar Radiation
119
3.3.7.2 Shading Strategies and Daylight
121
3.3.7.3 Solar Shading and Energy Related
Experiments
124
3.3.7.4 Solar Shading Design Methods
127
3.3.7.5 Solar Shading and Human Perception
128
3.4 Summary
4
129
METHODOLOGY
4.1 The Need for the Experiment
132
4.2 Development of Simplified Office Room
Configuration
133
4.2.1 Office Room Geometry
134
4.2.2 Window Size and Work Plane Height
134
4.2.3 External Overhang
135
4.2.4 Office Room Characteristics
137
4.3 Methods of Energy Evaluation
137
4.3.1 Simplified Energy Calculation Methods
138
4.3.2 Detailed Energy Calculation Methods
139
4.4 Methods of Studying Energy in Buildings
141
4.4.1 Manual Calculation Methods
142
4.4.2 Field Experiment or Full Scale Method
142
4.4.3 Computer Simulation
143
4.5 Selection of Computer Program
144
4.5.1 Experimental Requirement
145
4.5.2 Review of Energy Simulation Programs
146
xii
4.6 The eQUEST-3 Computer Simulation Program
4.6.1 Simulation Procedure
5
147
148
4.6.1.1 Step I: Data Requirement
149
4.6.1.2 Step II: Preparation of the Models
149
4.6.1.3 Step III: Detailed Interface-Selecting
Simulation Parameters and Perform
Simulation
155
4.6.1.4 Step IV: Review Simulation Results
157
4.6.2 Simulation Limitations
158
4.6.3 Simulation Design Conditions
160
4.6.3.1 Office Room Characteristics
160
4.6.3.2 Indoor Design Conditions
160
4.6.3.3 Internal Load
162
4.6.3.4 Operating Schedules
163
4.6.3.5 Outdoor Design Conditions
163
4.7 Simulation Analysis Criteria
165
4.8 Summary
169
RESULTS, ANALYSIS AND FINDINGS:
SOLAR RADIATION AND WORK PLANE
ILLUMINANCE
5.1 Incident and Transmitted Solar Radiation
171
5.1.1 East Orientation
172
5.1.2 West orientation
175
5.1.3 North Orientation
179
5.1.4 South Orientation
182
5.1.5 Influence of Solar Radiation Components on
Base Case Model
184
xiii
5.1.6 Impact of Overhang on Direct Solar Radiation
Incident on Window
188
5.1.7 Impact of Overhang on Diffuse Solar
Radiation Incident on Window
190
5.1.8 Impact of Overhang on Transmitted and ReTransmitted Solar Heat Gain through Window
System
191
5.1.8.1 Hourly Variation of Transmitted and
Re-Transmitted Solar Heat Gain
through Window System
5.2 Absolute Work Plane Illuminance
5.2.1 East Orientation
5.2.1.1 Window Height to Room Depth RatioEast Orientation
5.2.2 West Orientation
5.2.2.1 Window Height to Room Depth RatioWest Orientation
5.2.3 North Orientation
5.2.3.1 Window Height to Room Depth RatioNorth Orientation
5.2.4 South Orientation
5.2.4.1 Window Height to Room Depth RatioSouth Orientation
193
197
198
203
206
211
213
218
219
224
5.2.5 Hourly Variation of Work Plane Illuminance
226
5.2.6 External Horizontal Overhang and Work Plane
Illuminance
229
5.2.6.1 Impact of Overhang on Target
Illuminance Level (500lux)
229
5.2.6.2 Window Height to Room Depth Ratio
231
5.3 Summary
232
xiv
6
RESULTS, ANALYSIS AND FINDINGS:
ENERGY PERFORMANCE
6.1 Energy Evaluation
234
6.2. Building Component Cooling Loads
235
6.2.1 Base Case Generic Office Room and Building
Component Cooling Loads
235
6.2.2 Influence of External Horizontal Overhang on
Building Component Cooling Loads
237
6.3 Electricity Consumption
6.3.1 Annual Electricity Consumption- Base Case
6.3.1.1 Influence of Orientation on Annual
Electricity Consumption- Base Case
6.3.2
External Horizontal Overhang and Annual
Electricity Consumption
245
248
250
6.3.2.1 Incremental Electricity Use
254
6.3.2.2 Influence of External Horizontal
Overhang on Annual Electricity
Consumption
266
6.4 Summary
7
245
269
CONCLUSION
7.1 Review of Thesis Objectives and Research Questions
271
7.2 Thesis Conclusion
272
7.2.1 External Horizontal Overhang and Solar
Radiation
273
7.2.2 External Horizontal Overhang and Work Plane
Illuminance
275
7.2.3 Base-case Generic Office Room: Building
Component Cooling Loads
277
7.2.4 External Horizontal Overhang and Building
Component Cooling Loads
278
xv
7.2.5 Base-case Generic Office Room and Energy
Consumption
280
7.2.6 External Horizontal Overhang and Building
Energy Consumption
281
7.2.7 Optimum Overhang Ratios for Hot Humid
Tropical Climate
283
7.3 Application of the eQUEST-3 (DOE 2.2) Energy
Simulation in Malaysian Conditions
285
7.4 Suggestions for Further Research
286
BIBLIOGRAPHY
289
APPENDICES
305
A
Summary of Energy Related Research
306
C
Summary of High-rise Office Building and Energy Use
Review
C1
Office Buildings Energy Database, Kuala Lumpur
Malaysia
309
C2
South East Asian Office Buildings Information
312
C3
Design of Shading Device Considering the
Windows Solar Angle Dependent Properties: With
Special Reference to Kuala Lumpur Hot Humid
Tropical Climate
315
D
Review of Computer Simulation Programs
E
Simulation Data and Results
F
329
E1
Sample of Input Data
333
E2
Summary: Direct and Diffused Incident Solar
Radiation and Transmitted Heat Gains
338
E3
Summary: Work Plane Illuminance at Ref.Pt:01
and Ref.Pt:02
344
F1
Summary: Building Cooling Load Data
347
F2
Summary: End Use Energy Consumption Data with
Natural-light utilization
350
xvi
LIST OF TABLES
TABLE NO.
TITLE
PAGE
1.1
Summary of previous research related to solar shading,
daylight and energy use
8
2.1
ASHRAE (1999) clear sky model data for 21 day of each
month
24
2.2
Different Sky types according to Nebulosity Index, Subang
Jaya Malaysia
29
2.3
Comparison of measured SMS and DOE-weather file data
for hourly horizontal solar radiation for Kuala Lumpur
(2001) (Latitude: 3.120 , Longitude: +101.60,Time zone:
+7)
31
2.4
Monthly mean global horizontal solar radiations (W/m2)
and MBE & RMSE values for SMS and DOE.wf (Kuala
Lumpur)
32
2.5
Hourly direct normal solar radiations (x cloud cover) and
diffuse horizontal solar radiation (x cloud cover) - DOE.
wf. (Kuala Lumpur); (W/m2)
34
2.6
Percentage of direct normal solar radiation and diffused
horizontal solar radiation, DOE.wf for Kuala Lumpur
(2001)
34
2.7
Monthly mean values of DBT, WBT and DewPT and
correspondence Mean Bias Error (MBE) values
40
2.8
Horizontal exterior diffuse illuminance values (clear sky &
overcast sky) on 21 March, 22 June, 24 September and 21
December, DOE.wf (Kuala Lumpur)
45
2.9
Hourly maximum global exterior illuminance for 21
March, 22 June, 24 September and 21 December, DOE.wf.
(Kuala Lumpur)
45
xvii
2.10
Monthly maximum exterior illuminance values from clear
sky, overcast sky and direct sun, DOE.wf, (Kuala Lumpur)
46
3.1
Electricity intensity averages for ASEAN countries
52
3.2
Electricity consumption percentages by building
components for ASEAN countries
52
3.3
Optimum overhang ratio to intercept maximum direct
incident solar radiation; Latitude: 3.120, Longitude: +
101.60- East, West, North and South
101
3.4
Recommended average illuminance levels for office
buildings
112
3.5
Standard lowest exterior diffuse illuminance (lux) from
Sky for different climatic regions
114
4.1
Description of tested overhang depths of the experiment
136
4.2
Summary of shading strategy with design variables and
performance variables
151
4.3
Variables and constants of the study
165
4.4
Data analysis indicators and their interpretation
166
5.1
Summary of cumulative direct and diffuse solar radiation
incident and total transmitted heat gain for base case model
with percentage values compared to total incident solar
radiation on bare window
185
5.2
Summary of maximum intensity of direct and diffuse solar
radiation incident and total transmitted heat gain through
bare window on east, west, north and south orientations
187
5.3a
Maximum, minimum and mean work plane illuminance
values at ref. pt: 01, ref. pt: 02, and total solar heat gain- 21
March and 22 June, East orientation
202
5.3b
Maximum, minimum and mean work plane illuminance
values at ref. pt: 01, ref. pt: 02, and total solar heat gain- 24
September and 21 December, East orientation
203
5.4a
Maximum, minimum and mean work plane illuminance
values at ref. pt: 01, ref. pt: 02, and total solar heat gain- 21
March and 22 June, West orientation
209
xviii
5.4b
Maximum, minimum and mean work plane illuminance
values at ref. pt: 01, ref. pt: 02, and total solar heat gain- 24
September and 21 December, West orientation
210
5.5a
Maximum, minimum and mean work plane illuminance
values at ref. pt: 01, ref. pt: 02, and total solar heat gain- 21
March and 22 June, North orientation
216
5.5b
Maximum, minimum and mean work plane illuminance
values at ref. pt: 01, ref. pt: 02, and total solar heat gain- 24
September and 21 December, North orientation
217
5.6a
Maximum, minimum and mean work plane illuminance
values at ref. pt: 01, ref. pt: 02, and total solar heat gain- 21
March and 22 June, South orientation
223
5.6b
Maximum, minimum and mean work plane illuminance
values at ref. pt: 01, ref. pt: 02, and total solar heat gain- 24
September and 21 December, South orientation
224
5.7
Reduction percentages of cumulative direct, diffuse and
transmitted solar radiation for optimum overhang ratio for
target work plane illuminance level
231
5.8
Summary of optimum overhang ratio for incident solar
radiations, transmitted heat gains and work plane
illuminance
232
6.1
Annual cooling load (MWh) with natural-light utilization
and reduction percentage values as compared to base-case
model, for tested OHR-East orientation
238
6.2
Annual cooling load (MWh) with natural-light utilization
and reduction percentage values as compared to base-case
model, for tested OHR-West orientation
239
6.3
Annual cooling load (MWh) with natural-light utilization
and reduction percentage values as compared to base-case
model, for tested OHR-North orientation
240
6.4
Annual cooling load (MWh) with natural-light utilization
and reduction percentage values as compared to base-case
model, for tested OHR-South orientation
240
6.5
Summary of building cooling loads and reduction
percentages for optimum overhang ratio compared to basecase model, East, West, North and South orientations
242
xix
6.6
The annual total cooling load (MWh) with and without
natural-light utilization for base-case model and maximum
overhang option, East, West, North and South orientations
245
6.7
The annual electricity consumption for base case (w/o
shading devices) model, with and without natural-light
utilization, East, West, North and South orientations
247
6.8
Summary of impact of artificial lighting on space cooling
energy consumption for base-case generic office room,
East, West, North and South orientations
250
6.9
Regression coefficients as a function of overhang ratio for
incremental electricity use for area lighting (IEULt) - East,
West, North and South orientations
259
6.10
Regression coefficients as a function of overhang ratio for
incremental electricity use for space cooling (IEUCL) East, West, North and South orientations
260
6.11
Regression coefficients as a function of overhang ratio for
total incremental electricity use (IEUTOT) - East, West,
North and South orientations
261
6.12
Comparison of simulated (e-QUEST-3) to interpolated
(regression equation) IEUCL (kWh/m2, yr) for tested
overhang ratio
262
6.13
Comparison of simulated (e-QUEST-3) to interpolated
(regression equation) IEULt (kWh/m2, yr) for tested
overhang ratio
262
6.14
Comparison of simulated (e-QUEST-3) to interpolated
(regression equation) IEUTOT (kWh/m2, yr) for tested
overhang ratio
263
6.15
Summary of total energy saving and respective work plane
illuminance for optimum overhang ratio, East, West, North
and South orientations
267
6.16
Summary of energy saving for space cooling and
respective work plane illuminance for optimum overhang
ratio, East, West, North and South orientations
268
6.17
Summary of lighting energy consumption for optimum
overhang ratio for space cooling, East, West, North and
South orientations
269
xx
6.18
Summary of lighting energy consumption for optimum
overhang ratio for total energy consumption, East, West,
North and South orientations
269
7.1
Influence of maximum overhang ratio on direct, diffused
solar radiation and total transmitted heat gain, East, West,
North and South orientations
274
7.2
Trade-Off between optimum overhang ratios and
performance variables for direct incident solar radiation,
transmittance heat gain and mean work plane illuminance,
East, West, North and South orientations
277
7.3
Trade-Off between optimum overhang ratio and building
cooling load components, East, West, North and South
orientations
279
7.4
Summary of optimum overhang ratio for total energy
consumption and space cooling energy consumption
282
7.5
Summary of optimum overhang ratio for various
performance variables on east, west, north and south
orientations for tropical climate
283
xxi
LIST OF FIGURES
FIGURE
NO
TITLE
PAGE
1.1
The Problem: A typical fully glazed office space section
5
1.2
The Proposition: Optimum shading during over heated
period to reduce total heat gain and obtain target illuminance
5
1.3
User requirements for solar shading systems
13
1.4
The flow of research process and thesis structure
16
2.1
Comparison of global horizontal solar radiation between
SMS (measured) and DOE-wf (simulated) for Kuala
Lumpur- 21 March, 22 June, 24 September and 21 December
33
2.2
Hourly total solar radiations (direct & diffuse) on vertical
surface on 21 March
35
2.3
Hourly total solar radiations (direct & diffuse) on vertical
surface on 22 June
35
2.4
Hourly total solar radiations (direct & diffuse) on vertical
surface on 24 September
36
2.5
Hourly total solar radiations (direct & diffuse) on vertical
surface on 21 December
36
2.6
Hourly variations of dry bulb temperature (DBT) for 21
March, 22 June, 24 September and 21 December, DOE. wf.
for Kuala Lumpur
37
2.7
Hourly variations of wet bulb temperature (WBT) for 21
March, 22 June, 24 September and 21 December, DOE. wf.
for Kuala Lumpur
38
2.8
Comparison of monthly mean DBT (0C) data from SMS and
DOE.wf
38
xxii
2.9
Comparison of monthly mean WBT (0C) data from SMS and
DOE.wf
39
2.10
Monthly variation of Dew Point Temperatures (0C) data
from SMS and DOE.wf
39
2.11
Exterior horizontal illuminance for 21 March, DOE.wf data
for Kuala Lumpur
41
2.12
Exterior horizontal illuminance for 22 June, DOE.wf data for
Kuala Lumpur
42
2.13
Exterior horizontal illuminance for 24 September, DOE.wf
data for Kuala Lumpur
42
2.14
Exterior horizontal illuminance for 21 December, DOE.wf
data for Kuala Lumpur
43
2.15
Total exterior horizontal illuminance, DOE.wf data for Kuala
Lumpur
44
2.16
Calculated global luminous efficacies (lm/W), DOE.wf data
for Kuala Lumpur
44
2.17
Monthly maximum exterior illuminance values from clear
sky, overcast sky and direct sun, DOE.wf (Kuala Lumpur)
46
3.1
Examples of climate rejecting high-rise buildings in
Malaysia
56
3.2
Example of climate adapted building: Public Works
Department (PWD or JKR) building, Kuala Lumpur
57
3.3
Combination of climate adapted and rejected buildings in
Malaysia
58
3.4
Optimum high-rise building form according to climatic
zones
61
3.5
Arrangement of vertical core according to climatic zones
63
3.6
Core plan and annual cooling loads
63
3.7
Instantaneous heat balances through sunlit glazing material
73
3.8
External solar shading devices horizontal overhang, vertical
shading devices and egg-crate devices
89
3.9
Horizontal shadow angle (HSA)
90
xxiii
3.10
Vertical shadow angle (VSA)
91
3.11
The shadow angle protractor
92
3.12
Stereographic projections for Kuala Lumpur (Latitude 3.120,
Longitude +101.60, and Time zone 7)
92
3.13
Relationship between horizontal shading depth, window
height and vertical shadow angle (VSA)
93
3.14
Sideway extension of external horizontal shading device
94
3.15
Relationship between vertical fin’s depth, window width and
horizontal shadow angle (HSA)
94
3.16
Awning geometry
95
3.17
Relationship between external overhang depth, window
height and overhang ratio
100
3.18
Overhang ratio for side extension of horizontal shading
device
102
3.19
Effect of overhang on daylight distribution in a room
110
4.1
Base case office room configuration
135
4.2
Office room with overhang design
136
4.3
Sequential simulation approach
140
4.4
Simultaneous simulation approach
141
4.5
DOE 2.2 Simulation engine structure
148
4.6
Calculation procedure of loads from heat gains
149
4.7
Typical eQUEST-3 building wizard screen
150
4.8
The eQUEST-3 exterior window shades and blinds wizard
screen
152
4.9
The eQUEST-3 daylight zoning wizard screen
153
4.10
The eQUEST-3 HVAC system wizard screen
154
4.11
The eQUEST-3 detail interface screen
156
4.12
The eQUEST-3 hourly results selection screen
156
xxiv
4.13
The eQUEST-3 results screen of annual end use energy
consumption
157
4.14
The eQUEST-3 simulation procedures
157
4.15
Daylight photo sensor positions in office room model
161
4.16
Overall simulation procedures with design variables and
performance variables
168
5.1
Direct, diffuse solar radiation incident on window, and
transmitted and re-conducted solar heat gain (W/m2), as a
function of overhang ratio- 21 March, East orientation
173
5.2
Direct, diffuse solar radiation incident on window, and
transmitted and re-conducted solar heat gain (W/m2), as a
function of overhang ratio- 22 June, East orientation
173
5.3
Direct, diffuse solar radiation incident on window, and
transmitted and re-conducted solar heat gain (W/m2), as a
function of overhang ratio- 24 September, East Orientation
174
5.4
Direct, diffuse solar radiation incident on window, and
transmitted and re-conducted solar heat gain (W/m2), as a
function of overhang ratio- 21 December, East Orientation
174
5.5
Direct, diffuse solar radiation incident on window, and
transmitted and re-conducted solar heat gain (W/m2), as a
function of overhang ratio- 21 March, West orientation
176
5.6
Direct, diffuse solar radiation incident on window, and
transmitted and re-conducted solar heat gain (W/m2), as a
function of overhang ratio- 22 June, West orientation
177
5.7
Direct, diffuse solar radiation incident on window, and
transmitted and re-conducted solar heat gain (W/m2), as a
function of overhang ratio- 24 September, West orientation
177
5.8
Direct, diffuse solar radiation incident on window, and
transmitted and re-conducted solar heat gain (W/m2), as a
function of overhang ratio- 21 December, West orientation
178
5.9
Direct, diffuse solar radiation incident on window, and
transmitted and re-conducted solar heat gain (W/m2), as a
function of overhang ratio- 21 March, North orientation
179
5.10
Direct, diffuse solar radiation incident on window, and
transmitted and re-conducted solar heat gain (W/m2), as a
function of overhang ratio- 22 June, North orientation
180
xxv
5.11
Direct, diffuse solar radiation incident on window, and
transmitted and re-conducted solar heat gain (W/m2), as a
function of overhang ratio- 24 September, North orientation
180
5.12
Direct, diffuse solar radiation incident on window, and
transmitted and re-conducted solar heat gain (W/m2), as a
function of overhang ratio- 21 December, North orientation
181
5.13
Direct, diffuse solar radiation incident on window, and
transmitted and re-conducted solar heat gain (W/m2), as a
function of overhang ratio- 21 March, South orientation
182
5.14
Direct, diffuse solar radiation incident on window, and
transmitted and re-conducted solar heat gain (W/m2), as a
function of overhang ratio- 22 June, South orientation
183
5.15
Direct, diffuse solar radiation incident on window, and
transmitted and re-conducted solar heat gain (W/m2), as a
function of overhang ratio- 24 September, South orientation
183
5.16
Direct, diffuse solar radiation incident on window, and
transmitted and re-conducted solar heat gain (W/m2), as a
function of overhang ratio- 21 December, South orientation
184
5.17
Cumulative direct, diffuse and total incident solar radiation
and total transmitted heat gains for base-case model with
bare window on east, west, north and south orientations
186
5.18
Maximum intensity of direct and diffuse incident solar
radiation and total transmitted heat gain for base-case modelEast, West, North and South orientations
188
5.19
Reduction percentage (%) of cumulative amount of direct
solar radiation incident on window surface as function of
horizontal overhang ratio- East, West, North and South
189
5.20
Reduction percentage (%) of cumulative amount of diffuse
solar radiation incident on window surface as function of
horizontal overhang ratio- East, West, North and South
191
5.21
Reduction percentage (%) of cumulative transmitted and reconducted solar heat gain in an office room space as function
of horizontal overhang ratio- East, West, North and South
192
5.22
Maximum hourly total solar heat gains for tested overhang
ratios- East orientation
193
5.23
Maximum hourly total solar heat gains for tested overhang
ratios- West orientation
194
xxvi
5.24
Maximum hourly total solar heat gains for tested overhang
ratios- North orientation
194
5.25
Maximum hourly total solar heat gains for tested overhang
ratios- South orientation
195
5.26
Absolute work plane illuminance (lux) at ref.pt:01, ref.pt:02,
and solar heat gain (W/m2), as a function of overhang ratio21 March, East orientation
198
5.27
Absolute work plane illuminance (lux) at ref.pt:01, ref.pt:02,
and solar heat gain (W/m2), as a function of overhang ratio22 June, East orientation.
198
5.28
Absolute work plane illuminance (lux) at ref.pt:01, ref.pt:02,
and solar heat gain (W/m2), as a function of overhang ratio24 September, East orientation
199
5.29
Absolute work plane illuminance (lux) at ref.pt:01, ref.pt:02,
and solar heat gain (W/m2), as a function of overhang ratio21 December, East orientation
199
5.30
Mean work plane illuminance (lux) at reference point 01 for
tested overhang ratio- 21 March, 22 June, 24 September, and
21 December- East orientation.
204
5.31
Mean work plane illuminance (lux) at reference point 02 for
tested overhang ratio- 21 March, 22 June, 24 September, and
21 December- East orientation
204
5.32
Effect of overhang on natural light distribution in perimeter
office room- East orientation
205
5.33
Absolute work plane illuminance (lux) at ref.pt:01, ref.pt:02,
and solar heat gain (W/m2), as a function of overhang ratio21 March, West orientation
206
5.34
Absolute work plane illuminance (lux) at ref.pt:01, ref.pt:02,
and solar heat gain (W/m2), as a function of overhang ratio22 June, West orientation
206
5.35
Absolute work plane illuminance (lux) at ref.pt:01, ref.pt:02,
and solar heat gain (W/m2), as a function of overhang ratio24 September, West orientation
207
5.36
Absolute work plane illuminance (lux) at ref.pt:01, ref.pt:02,
and solar heat gain (W/m2), as a function of overhang ratio21 December, West orientation
207
xxvii
5.37
Mean work plane illuminance (lux) at reference point 01 for
tested overhang ratio- 21 March, 22 June, 24 September and
21 December for West orientation.
211
5.38
Mean work plane illuminance (lux) at reference point 02 for
tested overhang ratio- 21 March, 22 June, 24 September and
21 December for West orientation
212
5.39
Effect of overhangs on natural light distribution in perimeter
office room- West orientation
212
5.40
Absolute work plane illuminance (lux) at ref.pt:01, ref.pt:02,
and solar heat gain (W/m2), as a function of overhang ratio21 March, North orientation
213
5.41
Absolute work plane illuminance (lux) at ref.pt:01, ref.pt:02,
and solar heat gain (W/m2), as a function of overhang ratio22 June, North orientation
213
5.42
Absolute work plane illuminance (lux) at ref.pt:01, ref.pt:02,
and solar heat gain (W/m2), as a function of overhang ratio24 September, North orientation
214
5.43
Absolute work plane illuminance (lux) at ref.pt:01, ref.pt:02,
and solar heat gain (W/m2), as a function of overhang ratio21 December, North orientation
214
5.44
Mean work plane illuminance (lux) at reference point 01 for
tested overhang ratio- 21 March, 22 June, 24 September, and
21 December for North orientation
218
5.45
Mean work plane illuminance (lux) at reference point 02 for
tested overhang ratio- 21 March, 22 June, 24 September and
21 December for North orientation.
218
5.46
Effect of overhangs on natural-light distribution in perimeter
office room- North orientation
219
5.47
Absolute work plane illuminance (lux) at ref.pt:01, ref.pt:02,
and solar heat gain (W/m2), as a function of overhang ratio21 March, South orientation
221
5.48
Absolute work plane illuminance (lux) at ref.pt:01, ref.pt:02,
and solar heat gain (W/m2), as a function of overhang ratio22 June, South orientation.
221
5.49
Absolute work plane illuminance (lux) at ref.pt:01, ref.pt:02,
and solar heat gain (W/m2), as a function of overhang ratio24 September, South orientation
222
xxviii
5.50
Absolute work plane illuminance (lux) at ref.pt:01, ref.pt:02,
and solar heat gain (W/m2), as a function of overhang ratio21 December, South orientation.
222
5.51
Mean work plane illuminance (lux) at reference point 01 for
tested overhang ratio- 21 March, 22 June, 24 September and
21 December for South orientation.
225
5.52
Mean work plane illuminance (lux) at reference point 02 for
tested overhang ratio- 21 March, 22 June, 24 September and
21 December for South orientation.
225
5.53
Effect of overhangs on natural-light distribution in perimeter
office room- South orientation
226
5.54
Minimum hourly work plane illuminance at reference point
02, East orientation
227
5.55
Minimum hourly work plane illuminance at reference point
02, West orientation
227
5.56
Minimum hourly work plane illuminance at reference point
02, North orientation
228
5.57
Minimum hourly work plane illuminance at reference point
02, South orientation
228
6.1
Breakdown of annual cooling load (MWh) with natural-light
utilization and without natural-light for a base-case generic
office room- East, West, North and South orientations
236
6.2
Total envelop and internal component cooling loads (MWh)
for tested external horizontal overhang ratio, East, West,
North and South orientations
241
6.3
Total building space cooling load (MWh) for tested external
horizontal overhang ratio, East, West, North and South
orientations
242
6.4
Breakdown of annual cooling load (MWh) without naturallight utilization; for base-case model and maximum
overhang option, East, West, North and South orientations
243
6.5
The annual total cooling load (MWh) with and without
natural-light utilization for base-case model and maximum
overhang option, East, West, North and South orientations
244
6.6
Breakdown of annual electricity consumption for base case
model, with and without natural-light utilization- East, West,
North and South orientations
246
xxix
Total energy consumption with and without natural-light
scheme for base case model, East, West, North and South
orientations
247
6.8
(a & b)
Electricity consumption (kWh/m2, yr) for space cooling, area
lighting and total energy for tested overhang ratios, East &
West orientations
251
6.8
(c & d)
Electricity consumption (kWh/m2, yr) for space cooling, area
lighting and total energy for tested overhang ratios, North &
South orientations
252
6.9
Total annual electricity consumption for space cooling and
annual electricity consumption for cooling to remove the
heat gain from artificial lighting for different overhang ratio
tested- East, West, North and South orientations
253
6.10
(a & b)
Incremental energy use (kWh/m2, yr) for cooling, lighting
and total energy for tested overhang ratios- East and West
orientations
256
6.10
(c & d)
Incremental energy uses (kWh/m2, yr) for cooling, lighting
and total energy for tested overhang ratios- North and South
orientations
257
6.11
Energy saving percentage for space cooling and area lighting
incremental energy use as a function of overhang ratio, East,
West, North and South orientations
264
6.12
Energy saving percentage for total incremental energy use as
a function of overhang ratio, East, West, North and South
orientations
265
7.1
Several design option of external horizontal overhang
shading device
284
6.7
xxx
LIST OF ABBREVIATIONS
ASEAN
-
Association of South East Asian Nations
ASEAM
-
A Simplified Energy Analysis Method
ASHRAE
-
American Society of Heating, Refrigerating and Air
Conditioning Engineers
BC
-
Base Case
BDL
-
Building Description Language
BLAST
-
Building Loads Analysis and System Thermodynamics
CAD
-
Computer Aided Design
CBIP
-
Commercial Building Incentive Program
CIBS
-
Charted Institute of Building Service
CIBSE
-
Chartered Institution of Building Services Engineers
CIE
-
International Illumination Commission
COSLAM
-
Conference of Sri Lankan Malays
CTBUH
-
Council on Tall Building and Urban Habitat
DBT
-
Dry Bulb Temperature
DDM
-
Degree-Day Method
DewPT
-
Dew Point Temperature
DEU CL
-
Differential Energy Use (cooling)
DOE
-
Department of Energy (United States)
DOE.wf
-
Department of Energy weather file
EC LT
-
Energy Consumption (lighting)
EC CL
-
Energy Consumption (cooling)
EC TOT
-
Energy Consumption (total)
EEM
-
Energy Efficient Measures
eQUEST
-
Quick Energy Simulation Tool
GFA
-
Gross Floor Area
GIA
-
Gross Internal Area
xxxi
HVAC
-
Heating, Ventilation & Air-Conditioning
HSA
-
Horizontal Shadow Angle
IB
-
Intelligent Building
IES
-
Illuminating engineers society of North America
IES
-
International Energy Standards
IES
-
Integrated environmental Solutions
IEU
-
Incremental Energy Use
IEUCL
-
Incremental Energy Use (cooling)
IEULT
-
Incremental Energy Use (lighting)
IEUTOT
-
Incremental Energy Use (total)
LEO
-
Low Energy Office
LEED
-
Leadership in Energy and Environmental Design
MBE
-
Mean Bias Error
MDD
-
Modified Degree-Day method
MECM
-
Ministry of Energy, Communications & Multimedia
(Malaysia)
MEWC
-
Ministry of Energy, Water and Communication
(Malaysia)
MS
-
Malaysian Standards
NFRC
-
National Fenestration Rating Council
NI
-
Nebulosity Index
NRA
-
Net Rentable Area
OHR
-
Overhang Ratio
OHRé
-
Overhang Ratio (Side extension é)
OHRfin
-
Overhang Ratio vertical fins
ORI
-
Façade Orientation
OTTV
-
Overall Thermal Transfer Value
PC
-
Personal Computer
PF
-
Projection Factor
PSALI
-
Permanent Supplementary Artificial Lighting of
Interiors
PWD
-
Public Works Department
RMSE
-
Root Mean Square Error
SHGF
-
Solar Heat Gain Factor
SHGFv
-
Solar Heat Gain Factor vertical surface
xxxii
SHGFsh
-
Solar Heat Gain Factor shaded window
SMS
-
Subang Meteorological Station
SIR
-
Sun Illuminance Ratio
TMY
-
Typical Metrological Year
THG
-
Total Heat Gain
TRY
-
Test Reference Year
UMNO
-
United Malaya National Organization
USAID
-
Unite States Agency for International Development
UTM
-
Universiti Teknologi Malaysia
VE
-
Virtual Environment
VSA
-
Vertical Shadow Angle
WBT
-
Wet Bulb Temperature
WWR
-
Window-to-Wall Ratio
WYEC
-
Weather Year for Energy Calculations
xxxiii
LIST OF SYMBOLS
A
-
Surface Area (m2)
α
-
Absorptance (dimensionless)
A1, A2, A3
-
Coefficients of absorptions (constants)
A4, A5, A6
-
Coefficients of absorptions (constants)
Acog
-
Projected area center of glass (m2)
Aeog
-
Projected area edge of glass (m2)
Aframe
-
Projected area of frame (m2)
AG
-
Fraction of window area exposed to the sun (m2)
Ar
-
Rayleigh scattering coefficient
Asun
-
Area of window exposed to the sun (m2)
αb
-
Absorptance of reference glazing for direct beam
αdiff
-
Absorptance of reference glazing for diffuse radiation
B
-
Atmospheric extinction coefficient (dimensionless)
β
-
Solar altitude angle above the horizontal (0)
C
-
Diffuse sky factor
C1, C2, C3
-
Coefficients of transmission (constants)
C4, C5, C6
-
Coefficients of transmission (constants)
Cd
-
Compensation factor for window dirt (DF calculation)
Cf
-
Compensation factor for frame (DF calculation)
Cg
-
Compensation factor for glazing (DF calculation)
Cn
-
Clearness number of the atmosphere (dimensionless)
CR
-
Cloud Ratio
D
-
Depth of the horizontal projection (m)
δ
-
Solar declination angle (0)
d
-
Horizontal projection of the distance between the awning’s
lower corner and its shadow on the vertical wall (m)
DF
-
Daylight Factor
xxxiv
Ėdiff,cl
-
Clear sky diffuse illuminance (lux)
Edsky
-
Direct illuminance from sky (lux)
Er(ext)sky
-
External reflected component from sky illuminance (lux)
Er(int)sky
-
Internal reflected component from sky illuminance (lux)
d
sun
-
Internal direct illuminance from sunlight (lux)
Eirsun
-
Internal reflected illuminance from sunlight (lux)
Eo,sun
-
Exterior illuminance from sunlight (lux)
Eo,sky
-
Exterior illuminance from sky (lux)
Ei
-
Interior illuminance (lux)
Eo
-
Exterior illuminance (lux)
Et
-
Equation of time
e
-
Projection side ways from the window vertical edge (m)
e1
-
Length of the shading device over the window (m)
é
-
Awning width exceeding window width on each side (m)
φ
-
Latitude of the location (0)
Ffl
-
Flue loss factor, equipment
Fra
-
Radiation factor, equipment
Fs
-
Lighting special allowance factor
Fsg
-
Angle factor between the surface and the sky
Fss
-
Angle factor between the surface and the sky
Fu
-
Light use factor, lighting
Fua
-
Use factor, equipment
f
-
Depth of the vertical fin (m)
fr
-
Fraction of diffuse radiation obstructed by the shading device
γ
-
Surface solar azimuth (0)
G-value
-
Gref
-
Total fraction of incident solar energy
transmitted (dimensionless)
Reflectance of the ground
Gsunshade
-
G-value for corresponding shading device (dimensionless)
Gsystem
-
Gwindow
-
G-value for corresponding window system with
shading (dimensionless)
G-value for window (dimensionless)
η1, η2
-
Regression coefficients for total energy (dimensionless)
Hfen
-
Height of fenestration (m)
Hi
-
Inside air enthalpy, (kJ/kg) (dry air)
Ei
xxxv
Ho
-
Outside air enthalpy, (kJ/kg) (dry air)
h
-
Horizontal projection of the awning (m)
hi
-
Heat transfer coefficient, inside glazing surface (W/m2 K)
ho
-
Heat transfer coefficient, outside glazing surface(W/m2 K)
Isc
-
Solar constant
Io
-
Extraterrestrial solar radiation (W/m2)
Ibn
-
Direct beam normal solar radiation (W/m2)
Ibh
-
Direct beam solar radiation on horizontal surface (W/m2)
Ibv
-
Direct beam solar radiation on vertical surface (W/m2)
Idiff,h
-
Diffused solar radiation on horizontal surface (W/m2)
Idiff,v
-
Diffused sky radiation on vertical surface (W/m2)
IGh
-
Global irradiance horizontal surface (W/m2)
IGv
-
Global irradiance vertical surface (W/m2)
Ir
-
Ground reflected radiation (W/m2)
It,θ
-
Total horizontal radiation strikes the ground surface (W/m2)
Itot,h
-
Total solar radiation on horizontal surface (W/m2)
Itot,v
-
Total solar radiation on vertical surface
Icl,diff
-
Diffused solar radiation clear sky (W/m2)
İdv
-
Diffused & reflected radiation on vertical glazing (W/m2)
İbv
-
Direct beam radiation on vertical plane (W/m2)
Ї
-
Apparent extraterrestrial irradiance (W/m2)
Ídr
-
Direct solar radiation transmitted through standard
3mm clear glass
Ídf
-
Diffused solar radiation transmitted through standard
3mm clear glass
Ítot
-
Total (direct + diffused) solar radiation transmitted
through standard 3mm clear glass
ϕ
-
Awning slope (0)
K
-
Luminous efficacy (lm/W)
KB
-
Beam luminous efficacy (lm/W)
Kcc
-
Cloud cover ratio
KD
-
Diffused luminous efficacy (lm/W)
KG
-
Global luminous efficacy (lm/W)
k
-
Fraction of diffuse radiation obstructed by the shading device
xxxvi
L
-
Awning length (m)
λ1
-
Regression coefficient for lighting energy (dimensionless)
L edge
-
Length of window frame edge (m)
Lloc
-
Longitude of the location (in degree)
Lstd
-
Ltot
-
Standard meridian for the local time zone
(Longitude of the time zone)
Total Length (m)
m
-
Optical air mass
µ1, µ2
-
Regression coefficients for cooling energy (dimensionless)
N
-
Cloud amount
Ni
-
Inward flowing fraction of the absorbed radiation
No
-
Number of people
Nt
-
Cloud type
n
-
Daily sunshine duration
no
-
Maximum possible sunshine duration
pa
-
Atmospheric pressure
Q
-
Ventilation air flow (L/s)
θ
-
Incident angle (0)
θh
-
Angle of incidence on horizontal surface (0)
θv
-
Angle of incidence on vertical surface (0)
Qc
-
Conduction heat flow rate (w)
Qcl
-
Cooling energy use (W/m2)
Qel
-
Heat gain from electric lighting (w)
Qeq
-
Appliances heat gain (w)
Qi
-
Occupants heat gain (w)
Qs,win
-
Total solar heat gain flow rate, window (w)
Qv
-
Convection heat flow rate (w)
Qwin
-
Thermal heat gain, window (W/m2K)
ρ
-
Reflectance (dimensionless)
Rgap
-
Thermal resistance of gap between panes (m2K/W)
Rgl
-
Thermal resistance of glass pane (m2K/W)
Rsi
-
Internal surface resistance (m2K/W)
Rse
-
External surface resistance (m2K/W)
Rtot
-
Total thermal resistance (m2K/W)
xxxvii
R2
-
Coefficient of determination
S
-
Relative sunshine duration
SC
-
Shading coefficient
SC clearglass
-
Shading coefficient of clear glass
SCshadingdevice -
Shading coefficient of shading device
SC net
-
Net shading coefficient for partially shaded window
Sdf
-
Sky diffusive factor
Sec
-
Solar extinction coefficient
∆T
-
Temperature difference (0C)
τ
-
Τransmittance (dimensionless)
Td
-
Dew point temperature (0C)
Tdt
-
Out door dry-bulb temperature (0C)
Tsol
-
Local solar time
Tstd
-
Local standard time
Twt
-
Out door wet-bulb temperature (0C)
τa
-
Secondary heat transmittance (dimensionless)
τb
-
Transmittance of reference glazing for direct beam
(dimensionless)
τdiff
-
Transmittance of reference glazing for diffuse radiation
ti
-
Daily mean indoor temperature (0C)
to
-
Daily mean out door temperature (0C)
U
-
Thermal transmittance value (W/m2K)
Ucog
-
Thermal transmittance center of glass (W/m2K)
Ueog
-
Thermal transmittance edge of glass (W/m2K)
Uframe
-
Thermal transmittance frame (W/m2K)
UPD
-
Average lighting unit power density (W/m2)
Uwin
-
Thermal transmittance of window (W/m2K)
Vd
-
Wind direction
Vs
-
Wind speed
v
-
W
-
Vertical projection of the awning/ horizontal shading
device (m)
Total light wattage
ω
-
Solar hour angle (0)
Wawn
-
Width of the awning (m)
xxxviii
Wfen
-
Width of fenestration (m)
Wo
-
Outside humidity ratio, kg (water)/ kg (dry air)
Wi
-
Inside humidity ratio, kg (water)/ kg (dry air)
ψedge
-
Linear heat transmittance coefficient (W/mK)
ζ
-
Surface tilt angle (0)
xxxix
LIST OF APPENDICES
APPENDIX
TITLE
A
Summary of Energy Related Research
C
Summary of High-Rise Office Building and
Energy Use Review
PAGE
306
C1. Office Buildings Energy Data Base
Kuala Lumpur, Malaysia
309
C2. South East Asian Office Building
Information
312
C3. Design of Shading Device Considering the
Windows Solar Angle Dependent Properties:
With Special Reference to Kuala Lumpur
Hot and Humid Tropical Climates
315
D
Review of Computer Simulation Programs
329
E
Simulation Data and Results
F
E1. Sample of Input Data
333
E2. Summary: Direct and Diffused Incident
Solar Radiation and Transmitted Heat
Gains
338
E3. Summary: Work Plane Illuminance at
Ref.Pt:01 and Ref.Pt:02
344
Summary Building Energy Use
F1. Summary: Building Cooling Load Data
347
F2. Summary: End Use Energy Consumption
Data with Natural-light utilization
350
CHAPTER 1
GENERAL INTRODUCTION
1.1 Introduction
Protection of buildings against the influences of the climate and its forces had
been a challenging task throughout history. In modern scenario the task has been
more challenging by the fact that this protection should not categorically eliminate
all climatic influences, thus rendering the interior space independent from the
external environment. The most important facet of a building's internal environment
is the control of the physical conditions- light, temperature, humidity, airflow and
noise within the building (Codella et al, 1981). Unbalancing any of these conditions
will prevent the proper functioning of the building, as the comfort level for people
engage in the type of activity that the building is intended will be affected.
However, rapid pace of urbanization and development of technology played a part in
neglecting valuable experience of climate adopted building technology and often
controlled by artificial means. This is evident by the fact that intensive use of
electricity for lighting and air-conditioning to improve comfort levels has been major
consuming issues in high-rise office buildings.
The intensity of solar radiation in hot and humid climates such as Malaysia is
generally high and consistent throughout the year. Records of hourly solar radiation
data for altitude 3.70 north and latitude 101.30 east (Subang Jaya Meteorological
Station), received a maximum of 1055 W/m2 for the year 2001. This is about 7580% of the solar radiation intensity outside the earth’s atmosphere. Further, annual
maximum intensity of solar radiation falling on horizontal is about 1000 W/m2 and
2
on vertical surface is about 850 W/m2 for east and west facing surfaces. Thus, in
tropical hot and humid climates, solar radiation prevention is one of the crucial
factors in climate design criteria.
Daylight is one of the passive design strategies that architects and designers
can utilize in building design. What makes daylight utilization so interesting is that
it can be used to replace artificial lighting. Thus, it has two advantages in terms of
building energy use; firstly it reduces the electricity consumption for lighting and
secondly reduces the cooling demand through reduction of internal heat load from
lights. Other than energy saving and economical benefits, there are other
advantages and also potential drawbacks in daylight utilization. Use of daylight
implies the presence of windows in the immediate surrounding which has
psychological and physiological benefits. The quality of natural illumination may
also be highly desirable.
According to Nor Haliza (2002), Azni Zain-Ahmed (2002a) and Hamdan
(1996) the abundance of daylight in the tropics that has not been utilized to the
maximum, nor has it been considered as design criterion. The main drawback is
maximum daylight availability is usually concurrent with intense solar heat gain,
especially in hot and humid climates, like in Malaysia. Further, the sky conditions
in Malaysia can vary significantly throughout the day from overcast to clear sky, due
to formation of clouds (Hamdan, 1996). Therefore, availability of sunlight and
daylight can fluctuate significantly throughout the day. In this context, top lit
concept for daylight is not desirable and side lighting is the main source of daylight
into the building. The side daylight system produces a non-uniform light
contribution from window to wall at deep end of the room. Steep depth in ‘plan
form’ also creates gloomy interior where daylight penetration is limited. Another
main concern is glare caused by extreme contrasts or unsuitable distribution of
luminance. In order to avoid unbalanced conditions, artificial lighting is used to
create a brighter internal environment.
The high-rise buildings have significantly larger façade and fenestration area
than their low building counter part. The building vertical surface area is a major
3
variable in determining the impact of the climate forces, practically which cannot be
covered by a roof. The roof plays a significant role in controlling the climatic forces
in low rise buildings. Hence, high-rise buildings are more exposed to the full impact
of external temperatures, radiant heat and wind forces. Consequently by nature the
high rise buildings are energy intensive. The necessity to reduce energy use is
further challenged by the use of large glazing area for office buildings. Whether this
is the result of improvement in the glazing technology or to increase daylight levels
of the interior or aesthetic trend remains to be determined (Dubois, 2001c). Glass
facades create problems of overheating and high air-conditioning cost, excessive
brightness and discomforting glare problems.
Daylight and solar heat are two components directly affecting building
fenestration design. The main climate and energy conscious design initiatives in hot
and humid climates is to achieve a balance between solar radiation prevention and
daylight utilization (Lam and Li, 1999; Lee et al, 1998). The solutions remain in
thermal resistance of building envelope, preventing solar radiation falling on the
façade and allowing beneficial daylight in. Although use of tiny windows and tinted
glazing reduce heat gain through fenestration, they also cut off the view from the
window and tend to reduce the penetration of daylight into the space. Studies also
have shown that reducing window sizes do not prevent glare, but reduce amount of
daylight in the interior (Chauvel et al, 1982). But, heat reduction is best achieved by
excluding unwanted heat rather than removing it later, often by air-conditioning.
Previous researches (Dubois, 2000; Givoni, 1981; Harkness, 1978; Olgyay, 1957)
suggest that the use of appropriate solar shading devices can give better solutions to
solve the overheating, lack of daylight and glare problems in modern offices.
External shading devices also have a few advantages over other options like
different glazing types and reduction of window sizes. They can improve the light
distribution in the room and reduce the discomfort glare problem. Further, use of
shading devices are often more attractive to the architect than reducing the glazing
area or using reflective or tinted glazing, which may alter the architectural character
intended for the building (Dubois, 2001c).
4
Review by Abdul Majid (1996) and Nor Haliza (2002) of solar shading
designs in high-rise buildings in two major cities in Malaysia, Kuala Lumpur
(Latitude 3.70 N) and Johor Bahru (Latitude 1.380 N), showed that inappropriate
attentions given to the shading and daylight problems. According to Hassan, KAKU
(1996) most designers incorporate shading devices as an aesthetic element rather
than a useful climatic design element. The reasons may be of little knowledge on
solar radiation and daylight penetration and the energy implication often used to
achieve internal thermal and visual comforts. In this context it can be argued that
the role of external shading strategies required a rethinking in terms of reducing the
impact of solar radiation, obtain a better daylight distribution and energy
consumption for cooling and lighting.
1.2 The Problem Statement
Local climatic conditions affect the energy consumed by a building. In
Malaysia, buildings are subject to significant cooling requirements due to high
intensity of solar radiation penetration through fenestration. Previous works on
energy audits and surveys of office buildings for Malaysia indicated that the energy
consumed to cool the building is about 68% of the total electricity use (Loewen, J.M
et al 1992). The external solar shading devices can substantially reduce the cooling
load of buildings and large energy savings can be achieved.
However, a total shading to cut off unwanted solar radiation may reduce the
daylight level in buildings. A reduction in the use of daylight will increase in the
use of artificial lighting. This again results in the cooling load to remove the internal
heat gains from light as well as consume electricity on artificial lighting. Apart from
energy consumption, oversized shading devices reduce view out through building
which is a primary function of a window. In hot and humid climates, the problem is
emphasized by the fact that it is important to understand the magnitude of solar heat
gain, daylight penetration and high energy consumption in high-rise office buildings
in order to determine energy efficient shading strategy.
5
17.00 pm
09.00 am
Direct
sunlight
&
Diffused
light
Direct
sunlight
&
Diffused
light
Over heating
Increase in cooling load
High energy use
Over lighting
θ2
θ1
Glare
Figure 1.1: The Problem: A Typical Fully Glazed Office Space Section.
1.3 Research Hypothesis
The hypothesis of this study is that an optimum depth of a horizontal shading
device will achieve the following:
i. Reduction of solar heat gain into the building
ii. Obtain adequate daylight quantity at deep end of the interior space.
iii. Thus reduce the total energy consumption from cooling and lighting and
predict an optimum energy saving.
Direct sunlight is blocked
during the over heated period
9.00 am -17.00pm
Optimum shading depth
Reduction in cooling load
Reduction Solar heat gain
Total work plane
illuminance
θ
Optimum Energy
Increase
artificial
illuminance
500lux
Natural-light
illuminance
Figure 1.2: The Proposition: Optimum shading during over heated period to
reduce total heat gain and obtain target illuminance
6
The term “optimum depth” refers to the external horizontal shading device
depth which will reduce maximum heat gain and provide target illuminance to obtain
an optimum energy saving, by correlating between them.
1.4 Research Questions
The following questions will be addressed in this thesis:
1. Does the orientation of the fenestration influence the solar heat gain and
daylight penetration into the building and the depth of the shading device?
2. What are the effective overhang ratios to intercept the maximum direct and
diffuse incident solar radiations during the over heated period from 9:00 am
to 17:00 pm?
3. What is the effective overhang ratios for the maximum reduction of
transmitted heat gains during the over heated period from 9.00 am to 17.00
pm?
4. What is the effective overhang ratio to obtain adequate work plane
illuminance at deep end of the space considered?
5. Does the effective depth obtained at (2), reduce the work plane illuminance
below the target level?
6. What is the trade off between the transmitted heat gain and the shading depth
to achieve target work plane illuminance?
7. What is the optimum shading geometry to obtain an optimum energy saving
in relation to cardinal orientations?
1.5 Research Gap
Previous researches on solar shading were reviewed in order to get a clear
understanding of the state-of –art knowledge in the field and identify the areas which
had not been covered in the past. The review revealed that research on solar shading
7
had been focused mainly on five issues: impact on solar radiation, impact on daylight
quality and distribution, impact on energy use, shading design methods, and impact
on human comfort and perception. Few studies during the summer time and under
hot humid tropical climate suggested that use of external shading strategies
significantly reduce impinging solar radiation on the fenestration than the internal
shading devices (Olgyay and Olgyay, 1957; Givoni, 1998; Hassan KAKU, 1996).
Previous studies on external shading devices in hot and humid tropical climates
(Hassan KAKU, 1996; Sharifah and Sia, 2001) only concentrated on the incident
solar radiation (direct, diffused and reflected) and expressed the capacity of shading
device to cut out the impinging solar radiation. Yet they do not indicate amount of
solar heat gain transmitted into the space when different external shading strategies
were applied in order to understand the energy implication of employing such
strategies.
Though it was stated in many research works and publication that the external
solar shading reduces daylight distribution into the space, there were only few
researches done on this aspect in hot and humid tropical climate conditions (Sharifah
and Sia, 2004 Hamdan, 1996). Also, little is known about the relationship between
external shading device geometry and the daylight distribution, especially under high
illuminance global sky conditions like in Malaysia.
Review also suggested that shading strategies have a significant impact on the
energy consumption for cooling, heating and lighting. Few studies have looked into
this aspect under different climate conditions and with different shading strategies
(Bojic et al, 2002; Bülow-Hübe, 2001; Dubois, 1999; Huang et al 1992; Bordart et al,
2002; Li & Lam, 1999; Lee, E. S et al, 1998). Studies by Huang et al (1992) in
office buildings in Singapore, were dependent on other variables (different
illuminance levels, lighting power requirements, window-to-wall ratio) as well,
therefore it is difficult to derive clear conclusion on the effect of solar shading on
total energy consumption. Further they do not indicate an optimal shading strategy
for any particular climate. Hence, there is room for further research on relationship
between external shading device geometry and on the electric consumption for
cooling and lighting.
8
Table 1.1: Summary of previous research related to solar shading, daylight and
energy use
T
*
T
*
T
*
HH
*
HH
*
HA
*
*
*
Robbins
(1986)
T
*
Chirarttanano
n (1996)
HH
*
HH
Present Study
HH
*
*
*
* *
*
*
T = Temperate climate
climate
Others
Design Meth
Energy
Glare
Uniformity
*
*
*
*
*
*
*
*
*
*
*
*
*
*
*
*
*
*
*
*
*
*
√
*
*
*
*
HH
Bojic (2002)
*
*
HA
HH
*
Visual
*
*
HH
Al-Shareef
(2001)
Dinapradipta
(2003)
Huang
(1992)
*
*
Temperature
*
*
Solar transmit
*
Color
T
Thermal
Solar radiation
*
Angle
*
Depth
*
Width
HH
Geometry
Window-to-wall
*
Glazing
Build.
orientation
vegetation
*
Blinds
Egg-crate
*
Screens
Vertical
T
Internal
Awnings
Horizontal
Olgyay
(1957)
Hassan,
KAKU
(1996)
Givoni
(1981/1998)
Dubois
(1999)
Dubois
(1998)
Dubois
(2001c)
Sharifah &
Sia
(2001)
Sharifah &
Sia
(2004)
Raeissi &
Taheri (1997)
Azni ZainAhmad
(2002)
Climate zone
Research
External
Performance Variable
Natural
Illuminance
Design Variables
*
*
*
*
*
*
*
*
*
*
*
*
*
*
*
*
*
*
√
HA = Hot and arid climate
√
√
√
√
HH = Hot and humid
Table 1.1 gives a summary of related research work and their variables.
Thus, the above review suggest that effect of solar shading on solar heat gain,
internal daylight level and on energy consumptions have been dealt as separate
9
issues. There is no specific research done to study the relationship between external
shading devices and the correspondence solar heat gain, daylight level and energy
consumptions. Therefore, this thesis attempts to focus on the application of external
horizontal solar shading device and to asses their performance with respect to the
impact of solar radiation, internal daylight illuminance level and the optimal energy
saving.
1.6 Research Objective
The main objective of this study is to assess and evaluate the impact of
external horizontal shading devices in reducing the unwanted solar heat gain and the
amount of daylight penetration into the building. Thereby, to determine the
geometry of horizontal shading device to optimize the energy savings for cooling and
lighting for buildings in hot and humid climates.
Other specific objectives of the study are as follows:
1. To determine the amount of direct, diffuse and reflected solar radiation
incident on the window pane and transmitted solar radiation through window.
2. To determine the depth of external horizontal shading device considering the
window solar angle dependent properties.
3. To determine the direct, diffuse and reflected solar radiation incident on the
window pane and transmitted solar radiation through the window for the
proposed external horizontal shading devices described in (2).
4. To determine the work plane illuminance for the proposed external horizontal
shading devices described in (2).
5. To determine the potential trade-offs involved between the solar heat gain
and daylight penetration into the interior space to optimize the depth of the
external horizontal shading devices described in (2).
6. To determine the energy performance of proposed external horizontal shading
devices described in (2).
10
7. To compare the energy performances of proposed external horizontal shading
devices with a base-case model (without shading device) and results obtained
from (3), (4) and (6) for determining the optimum overhang depth to achieve
optimum energy saving.
8. To determine the influence of building orientation on the external horizontal
shading strategy.
1.7 Scope and Limitations
There are several necessities for using shading systems in buildings, ranging
from individual level (better thermal and visual comforts, low energy bills) to
national or global levels (reducing energy consumptions). However, scope of this
study is to evaluate the solar heat gain and daylight penetration in order to optimize
the energy consumption for cooling and artificial lighting when external solar
shadings are applied.
The thermal performance of a building largely depends on two parameters:
unsteady climatic parameters and building design variables (Bouchlaghem, 2000).
The thermal analysis is mainly focused on the amount of direct, diffuse solar
radiation and transmitted and retransmitted solar heat gain through fenestration.
Although, there are other means of solar heat gain into the building such as,
conduction through wall and infiltration, assumptions are made that heat gain from
these modes are constant for all the tested shading strategies. Further, relative
humidity and wind flow also can effect on the building thermal performances, but
these parameters were not considered in this experiment.
The thermal comfort aspect is not dealt within this thesis as a major issue.
This is because there are other parameters effecting thermal comfort, for e.g. air
temperature, humidity, air velocity, clothing and metabolic heat production (Givoni,
1981; Sharifah, 1995). It is assumed that by setting the indoor temperature at
recommended comfort value, will provide the required thermal quality for that space.
11
The daylight evaluation is limited to determining the work plane illuminance
at 0.9 meter from the ground level. Uniformity of daylight distribution, luminance
ratio between the surfaces of the space, effects on color rendering and effect on glare,
which contribute to the determining the qualities of daylight of a space are not dealt
in this thesis. Although evaluation of daylight quality is not within the scope of this
study, assumptions were made, by providing an optimum shading strategy so that
these criteria were acknowledged, thus provide appropriate visual comfort for the
user.
The energy performance of a building largely depends on three parameters;
building design variables, mechanical and technical system efficiency and efficient
management of systems. An approach focusing on architectural form and envelope
are directly under the control of the architect and also provides a visual picture of the
impact of environment on people and architecture. In this study energy analysis is
carried out for different external horizontal shading geometry only. Other building
design parameters such as, properties of building materials, location and size of
fenestration, surface treatment and insulation were kept as constant to all shading
cases tested.
Mechanical and technical system operating conditions were also kept
identical to all experiments tested. The working schedule for the office is considered
from 9:00 am to 17:00 pm.
A standard office room with a single fenestration was selected for the
experiment, with a typical room configuration capturing the variety of solar heat
gains and lighting distributions found in typical high-rise office buildings in
Malaysia. Therefore, analysis of data and energy is performed and discussed as
reference to the base case model and as a ratio to the base case values. The base case
office room is developed to comply with the Malaysian MS 1525 Standards. Due to
above stated reasons; no comparisons were made with any existing building energy
estimates.
12
This study is entirely carried out by using computer simulation program
eQUEST-3 DOE 2.2 (Version 3) and thus bears the limitations of the simulation tool
used. In chapter 4, a review on common research methods used by previous
researches and justification for the selection of the present tool are discussed.
Finally, the simulation is performed under clear sky conditions and the main
cardinal orientations, East, West, North and South, were considered. The following
days were chosen for hourly analysis; 21 March, 22 June, 24 September and 21
December. Since Malaysia receives similar climatic condition throughout the year,
the selected dates do not represent extreme days or average days, but suggest the
position of the sun related to certain façades at certain orientations. During 21 March
and 24 September the sun is within the plane of the equator and in tropical regions, a
high amount of solar radiation is received on these dates. In 22 June and 21
December the sun is in the equinox and it is at farthest point from the tropical region.
Therefore it is assumed the impact of solar radiation is less on these two dates
compared to other dates of the year.
1.8 Importance of the Research
The out come of the study is expected to show that, the effectiveness of the
solar shading system depends on the relative balance between solar heat gain
reduction and adequate daylight in the building. The study also expect to suggest
that appropriate design decisions on solar shading systems can significantly reduce
the high energy consumption in office buildings in Malaysia.
Apart from the protection against harsh solar radiation and energy
conservation, the use of solar shading has benefit on various other aspects as shown
in figure 1.3. The most important aspect is the thermal and visual comforts, which
determines the human behavior. Hence, findings of this study will enable and
provide the building designer with wider range of options in selecting an appropriate
13
shading strategy for achieving the balance between desired daylight level and
optimum energy consumptions for space cooling and lighting.
Requirements on Solar
shading systems
Thermal
comfort
Aesthetic
requirement
-Protection from
unwanted solar heat
gains
-Induce internal air
flow
Visual
comfort
-Provide adequate
daylight
- Uniform
illuminance in the
room
- Glare protection
- Provide adequate
privacy and view out
- Provide visual
quality
Figure 1.3:
Low
cost
Reduce
energy
consumption
-Reduce cooling
load
-Reduce lighting
energy consumption
-Reduce total
electricity demand
Reliability
and
compliance
with
technical
aspects
Protection
against:
fire, noise,
weather,
burglary
User requirements for solar shading systems
1.9 Thesis Organization
The thesis is organized into eight chapters as summarized bellow.
Chapter one introduces the main issue of this research. This chapter also
contains the proposed hypothesis of the study, research questions, and objectives of
the study. Further, the research gap, scope and limitations of the study and the overall
thesis structure are also presented in this chapter.
Chapter two reviews the theory of solar radiation and the sky conditions of
Malaysia, particular to Kuala Lumpur (Latitude: 3.120; Longitude: +101.60; Time
zone: +7). Review on solar radiation includes the geometry of solar movement,
solar intensity and its computations for different radiation types in order to
understand their influence on the building. Also, a critical evaluation is carried out
14
between measured weather statistics for the location considered and data obtained
from the simulation weather file in order to clarify the validity of the latter to be used
in the study.
Chapter three is divided into three sections. Section one reviews the energy
consumption patterns in Malaysia in general and in office buildings in particular.
The building standards for energy control in commercial buildings are also reviewed
to understand the energy scenario in Malaysia. The high-rise office building and
basic principles of energy efficient high-rise building are discussed. Based on the
review initial design conditions for the present study are also presented. Section two
reviews the principles of heat gains, types of heat transfer and factors influencing
heat gains in the building. A method to compute the solar heat gains are explored.
Finally, in section three, different shading devices are analyzed to understand their
implication as a shading element. Their basic functions as a solar radiation control
device are discussed to get a clear understanding of the state-of-the-art knowledge in
the field. Aspects determining the effectiveness of the shading are presented in order
to find a suitable energy efficient shading strategy. Methods for designing shading
device are reviewed and a new method is proposed to determine the shading depth in
hot and humid climate conditions.
Chapter four discuss the methodology implemented in this present study.
Initially, the energy evaluation methods and common research methodologies used
by previous researchers are reviewed. Thus, an appropriate methodology to be
employed in this thesis is formulated. Further, development of the base model,
experimental procedures, assumptions, limitations and the overall sequence of the
selected experiment method are described. Finally, the data analysis criterions are
discussed, which is used to analyze the results of the experiment.
Chapter five presents the results and analysis of the incident solar radiation
transmitted solar heat gain and work plane illuminance for the tested external
horizontal shading strategies. The principle findings of the simulation are also
summarized. The results of the simulation are analyzed as follows:
15
o
Assess the impact of shading strategies on incident solar radiation (direct
& diffused).
o
Assess the impact of shading strategies on transmitted solar heat gain into
building.
o
Assess the influence of shading strategies on target illuminance level at
deep end of the room to determine the optimum shading strategy for
natural-lighting.
o
Assess the relationship between natural-light penetration and the office
room geometry.
Chapter six investigates the influence of the external horizontal overhang
strategies on building cooling load and energy consumptions. The results of the
experiments are analyzed as follows:
o
Assess the impact of shading strategy on annual building cooling load.
o
Assess the impact of shading strategy on annual energy consumption for
cooling, lighting and on total consumption to determine the optimum
energy consumption.
o
Assess the natural-light level and annual energy consumption to determine
the optimum shading strategy.
Chapter seven presents the overall review of the thesis objectives and
research questions, followed by the conclusion remarks of the major findings of the
experiment. Finally, suggests further works to complement with the thesis findings.
16
Thesis Problem
Literature Review
Solar Radiation and
Malaysian Sky
Condition
Chapter 2
Energy use in High-rise
Office Buildings and
Solar Shading
Chapter 3
Methodology
Chapter 4
(Computer
Simulation)
Results and Analysis
Chapter 5 & 6
Conclusion
Chapter 7
Figure 1.4 The flow of research process and thesis structure
CHAPTER 2
SOLAR RADIATION AND ANALYSIS OF MALAYSIAN SKY
CONDITIONS
This chapter reviews the solar radiation and analyses the Malaysian sky
conditions, which is divided into two parts. The first part includes sub sections from
2.1 to 2.4; while part two consist of sub section 2.5. The part one briefly reviews the
characteristic of the solar energy, definitions and models developed to predict the
impinging solar radiation on the earth’s surface. The second part analyses the
Malaysian sky conditions with measured and calculated data. Initial information on
Malaysian sky conditions were gathered from previous studies and data obtained
from the local meteorological stations. The calculated data for Kuala Lumpur are
obtained from the DOE 2.2 (Department Of Energy) weather processor and is
considered as the corresponding location of the present study.
Accurate climatic data is important in many applications. These include
determining the design of the building, mechanical system and evaluation of indoor
climatic performance for a better energy efficient approach. Under-estimating
climatic impacts would result on occupant’s well being and the performance of the
task. In contrast, overcautious approach may result in oversize of plants and high
energy consumptions.
2.1 Solar Radiation: Source of Heat and Light
The sun emits energy to space in the form of electromagnetic radiation.
Practically it is the only source of energy that influences atmospheric motions,
18
various processes in the atmosphere and on the surface layer of the earth. The
electromagnetic radiation that intercepts at earth's atmosphere is converted to form of
'heat' or 'entropy' and to 'spectrum' energy. Depending on the aspect of radiation
field; either entropy or the spectrum system, the quantitative characteristics of solar
radiation are defined. In thermodynamic field, studying the 'entropy' effects of the
radiation field involves the interest on consideration of the heat released per unit time
in full absorption of the radiant flux (Kondratyev, 1969). In the spectrum field, light
is the visual manifestation of the radiant energy. The visible radiant energy is
measured by the rate of energy transfer evaluated in terms of its effect on the average
human eye (Kondratyev, 1969). Hence, it is intimately related to the human
sensation. However, by defining light in purely physical terms, it can distinctively
differentiate the physical quantity without the aid of the human eye (Hopkinson,
1966). Practically the spectrum effect also connected with transfer of a certain
amount of radiant entropy to the receiver. Therefore, both systems are interrelated,
but the quantitative characteristics of a radiation field can be differentiated between
heat energy and the photometric effect.
2.2 Solar Geometry
The sun is the source of energy that influences the atmospheric motion and
the earth's climate. Evidently, the intensity of solar radiation received at the earth
surface varies significantly with the seasons and over the course of the day.
Therefore to understand the trigonometric relationship between earth and the sun is
an important factor in determining the intensity of the solar radiation incident on
earth surface. The sun's apparent position in the imaginary sky dome is given by the
altitude and azimuth angles. Altitude is defined as the angle between the horizontal
plane and the solar direct beam, while azimuth give the solar position measured from
the north direction towards east or west. Solar altitude varies with latitude, as the
earth is spherical. Solar altitude also influences the interaction between insolation
and the atmosphere. Decrease in solar altitude angle increases the distance of solar
path through atmosphere. As solar path lengthens, the radiation interact more with
aerosols of the atmosphere and its intensity diminishes.
19
The ecliptic orbital plane of the earth and the angle between the earth’s
equator and ecliptic plane causes unequal effects of the solar radiation at different
orientations. During 21 March and 24 September the sun rotates above the equator.
These days are known as equinox days as the day and night are of equal length.
Further, on 21 March and 24 September, areas along the equator receive the
maximum intensity on a surface normal to the direction of radiation. However, due
to the tilted position (tilt of 23.50 from the normal) the area receiving the maximum
intensity moves north and south between tropic of Cancer (latitude 23.50 N) and the
tropic of Capricorn (latitude 23.50 S). On 22 June, the sun is in the north solstice and
on 21 December it is in the southern solstice. During solstice periods the sun
location is farthest from the equator. Thus, areas along latitude 23.50 N and 23.50 S
experiences the longest daylight period on respective correspondence days. At the
same time 23.50 towards south and 23.50 towards north receives the minimum
radiation and experiences the shortest days respectively.
2.3 Solar Distribution
Electromagnetic radiation travels as waves, which are described in terms of
wavelength frequency. The spectrum of the solar radiation extends from 290nm to
2500nm. The division of the radiation spectrum from 290- 380nm is known as the
ultraviolet radiation, characterized by the fact of producing photochemical effects,
bleaching and sunburns. The human eye is sensitive to radiation of 380- 700nm,
which is the visible spectral region. Radiant heat with photochemical effect is
generated by short infrared radiation spectrum from 700- 2500nm (Koenigsberger, et
al 1973). Further investigations has indicated that, practically all the radiant energy
of direct, diffuse and reflected radiation falls in the region of short wavelengths. The
thermal radiation of the earth surface and the atmosphere has on the contrary a long
wave characteristic. The long wave radiation of the earth surface is often called
'terrestrial radiation' (Kondratyev, 1969).
20
2.3.1 Solar Intensity
The intensity of radiation is the main quantitative characteristic of the
radiation field. By definition, solar constant (Isc) is the intensity of radiation of a
surface, which depends on the wavelength of radiation, on a unit surface area and on
the solar altitude. Maximum intensity occurs when the surface is normal to the sun's
rays. The value measured for solar constant varies from a maximum of 1414 W/m2
to a minimum of 1323 W/m2.
The extraterrestrial solar radiation (Io) is the intensity of solar radiation
outside the earth’s atmosphere on a surface perpendicular to the sun’s ray. The direct
and diffuse radiation on earth surface under clear sky conditions are derived from the
extraterrestrial solar radiation. The extraterrestrial solar radiation is calculated using
ASHRAE (1999) model:
Io = [1+ 0.033 cos {360 0 x n / 365}] x Isc
(2.1)
Where ‘n’ is the day of the year. The ASHRAE (1999) value 1367 W/m2 is
taken as solar constant (Isc). The main dependent parameter is the day of the year (n)
and it is independent of solar position (or solar hour angle) and latitude of the site.
Hence, any location on the earth surface will receive the same amount of
extraterrestrial solar radiation.
2.3.2 Components of Solar Radiation: Direct, Diffuse and Reflected Radiation
The radiant energy of the sun undergoes complicated transformations as it
passes through the atmosphere. 'Absorption' and 'scattering' of radiant energy take
place when travelling from the outer boundary to the earth surface. These
transformations of radiant energy create 'direct solar radiation' and 'diffuse radiation',
falling from every point of the sky. The direct solar radiation and diffuse radiation
comprise 'global radiation'. On reaching the earth, the global radiation is partly
21
reflected by the earth's surface and a flux of 'reflected radiation' thus appears. The
unreflected part of the direct solar radiation and diffuse radiation is absorbed by the
earth's surface; natural and man made elements, and thus constitutes as 'absorb
radiation'. The heat released in the absorption of the global radiation becomes a
source of ‘thermal radiation' of the earth surface directed to the atmosphere. In
contrary, atmospheric radiation emits thermal radiation surface ward (downwards).
Therefore, the value of radiative heat exchange between earth's surface and the
atmosphere is characterized by the concept of 'effective radiation'. In other words it
is the difference between the thermal radiation of the earth's surface and the
downward atmospheric radiation.
When solar radiation wave strikes a particle (aerosol) in atmosphere, it
changes the direction of incoming radiation. This scattered energy is call diffused
radiation. This diffuse radiation in turn strikes other molecules and particles and thus
the scattering process continues. The frequency and the energy of the scattered
component do not change, but the change in direction leads to changes in the
intensity of the light. The scattering of the particles and the wavelength of the
striking beam is differentiated into two distinct effects. The scattering from
molecules are in two forms. The air molecules smaller than the wavelength are
known as Rayleigh scattering (This was first identified by Rayleigh in 1871).
Likewise, when the particle size is in order or larger than the wavelength of the
incident radiation, a Mie scattering occurs. Hence, the densities of the aerosols
create an air mass in the atmosphere. The scattering depends strongly upon the
frequency of the radiation. The spectral energy distribution varies with solar altitude,
due to the filtering effect of the atmosphere. The lower the solar altitude angles the
longer the path of radiation through the atmosphere. However, the maximum
intensity is received on a plane normal to the direction of radiation. The cosine law
is applicable when the intensity on a tilted surface equals the normal intensity times
the cosine of the angle of incidence (Koenigsberger et al, 1973). Depending on the
direct solar radiation, diffused solar radiation and global radiation, several solar
radiation models were developed to calculate the solar intensity on a horizontal
surface and a vertical surface under different sky conditions (Wong & Chow, 2001).
22
2.4 Solar Radiation Calculation
Solar radiation availability depends on two factors. Firstly, the suns position
in the sky which is given in terms of solar altitude and azimuth angles. Secondly, the
sky conditions which is predicted in terms of sky clearness or on the amount of air
mass. Knowledge of the local solar radiation is essential for proper design of
building energy systems and evaluation of thermal environment within buildings.
According to the acquired information, solar radiation calculation models can be
categorized into two models (Wong, 2001). They are ‘parametric model’ and
‘decomposition model’. The parametric model requires detail information of
atmospheric conditions, such as, cloud type, cloud amount, cloud distribution,
fractional sunshine, atmospheric turbidity and water contents (Iqbal, 1983;
ASHRAE, 1999). In decomposition model information on global radiation is used to
predict the beam, diffused and sky components (Liu et.al, 1960; Lam et.al, 1996).
As reviewed by Wong and Chow (2001), the parametric model would
provide accurate predictions of solar radiation for good evaluations of thermal
environment in buildings than the decomposition model. However, if precise
atmospheric information is not available, decomposition model based on measured
hourly global radiation would be a good choice. Further details of the methods used
to calculate the solar radiation are described in various publications and text books
written by Iqbal, 1983; Liu et.al, 1960; Lam et.al, 1996; Al-Riahi M, et.al, 1998;
Muneer et.al, 1998 and ASHRAE, 1999.
In the field of architecture and engineering the model adopted in ASHRAE
(1999) is widely used. The following calculations of the solar radiation on horizontal
and vertical surfaces are based on the ASHRAE clear sky model.
23
2.4.1 Calculation of Clear Sky Solar Radiation
a. The direct beam normal solar radiation (Ibn) is given by:
Ibn = (Cn) (Io) e (-B/ sinβ)
(2.2)
Where Cn (dimensionless) is the clearness number of the atmosphere. Io is
apparent extraterrestrial irradiance (W/m2), B (dimensionless) is atmospheric
extinction coefficient and β is the solar altitude angle above the horizontal. The
value of sinβ is calculated from:
Sinβ = sinφ.sinδ + cosφ.cosδ.cosω
(2.3)
The latitude of the location is φ, δ is the solar declination angle and ω is the
solar hour angle. The solar hour angle ω (in degrees) given by the local solar time
(Tsol) as:
ω = 15 (12:00 - Tsol)
(2.4)
The solar noon is assumed to be as zero mark and each hour equivalent to 150
of longitude where as morning (+) and afternoon (-). The local solar time (Tsol) is
calculated from the local standard time (Tstd) and the equation of time (Et), is given
by:
(Tsol) = Tstd + Et + 4( Lstd-Lloc)
(2.5)
where Lstd is the standard meridian for the local time zone (longitude of the
time zone) and Lloc is the longitude of the location in degree (00 < Lloc < 3600).
The ASHRAE (1999) model solar data for clear sky for each month are given
in Table 2.1. It specifies values for nine parameters; Ї, B, C, Et, δ, φ, Lstd, Lloc and
Tstd.
24
Table 2.1: ASHRAE (1999) clear sky model data for 21st day of each month
Month
Jan
Feb
Mar
Apr
May
Jun
Jul
Aug
Sep
Oct
Nov
Dec
Ї
(W/m2)
(W/m2)
B
C
Equation time
(minutes) Et
Declination
(degrees) δ
1416
1401
1381
1356
1336
1326
1326
1338
1359
1380
1405
1417
1230
1215
1186
1136
1104
1088
1085
1107
1151
1192
1221
1233
0.142
0.144
0.156
0.18
0.196
0.205
0.207
0.201
0.177
0.16
0.149
0.142
0.058
0.06
0.071
0.097
0.121
0.134
0.136
0.122
0.092
0.073
0.063
0.057
-11.2
-13.9
-7.5
1.1
3.3
-1.4
-6.2
-2.4
7.5
15.4
13.8
1.6
-20
-10.8
0
11.6
20
23.45
20.6
12.3
0
-10.5
-19.8
-23.45
Io
2.4.2 Solar Radiation Calculations on Horizontal Surfaces
a. Beam (direct) radiation (Ibh) is given by:
Ibh = Ibn cos θ
(2.6)
b. Diffuse radiation (Idiff) is given by:
Idiff = C(Ibn)
(2.7)
Where for horizontal surface C is the sky diffusive factor
c. The total solar radiation (Itot,h) on horizontal surface is:
Itot,h = Ibn cos (θh) + C(Ibn)
(2.8)
The incident angle θ is related to solar altitude (β), surface solar azimuth (γ)
and surface tilt angle (ζ).
Cos (θ) = cosβ cos γ sinζ + sinβ cosζ
(2.9)
25
When the surface is horizontal;
(ζ) = 00
Cos θh = sin β
For vertical surface;
(ζ) = 900
Cos θv = cosβ cos γ
Where, θh and θv are the angles of incidence on horizontal and vertical
surfaces respectively.
2.4.3 Solar Radiation Calculations on Vertical Surface
a. Beam (direct) radiation (Ibv) is given by:
Ibv = Ibn cos (cosβ cos γ )
(2.10)
b. Diffuse sky radiation (Idiff,v) given by:
Idiff,v = C (Ibn) Fss
(2.11)
Where Fss is the angle factor between the surface and the sky, is given by
Fss = (1+cosζ)/ 2
For vertical surface cos (ζ) = 0
c. Ground reflected radiation (Ir) given by:
Ir = It, θ Gref. Fsg
(2.12)
Where It, θ is the total horizontal radiation strikes the ground surface (θ=00).
Gref is reflectance of the ground and Fsg is the angle factor between the surface and
the sky is given by:
26
Fsg = (1-cosζ)/ 2
d. The total global radiation on vertical surface is (Itot, v) given by:
Itot, v = Ibv + Idiff, v + Ir = I’BN cos (cosβ cos γ ) + C (Ibn) Fss + It, θ Gref Fsg
(2.13)
2.5 Analysis of Kuala Lumpur Sky Conditions
A major draw back in using meteorological parameters is that of its scarcity
and unavailable data except at limited geographical locations. Obtaining daily
measurements are also time consuming and disperse location wise. Therefore in
simulation models, average values, spatial interpolation, estimates from remote
sensing and estimates obtained from models based on available climatic data have
been suggested (Al-Sanea, 2004). As an alternative, numbers of climate prediction
models have been recommended to estimate different climatic parameters with
varying degree of details and accuracy.
Relevant data of weather elements were extracted from the DOE-2 weather
processor; Asian-sp files, for Kuala Lumpur; Latitude: 3.120, Longitude: +101.60 and
Time zone: +7. The weather data is derived from weather tapes supplied by the
national climatic centres of particular country or region. These weather tapes are
generated based on monthly mean climatic variables; out door dry-bulb temperature
(Tdt), out door wet-bulb temperature (Twt), atmospheric pressure (pa), cloud amount
(N), wind speed (Vs), cloud type (Nt) and wind direction (Vd). When information is
missing for one or more hours, Tdt, Twt, pa, N and Vs are linearly interpolated from
previous available value to next available value. The other variables are calculated
using mathematical formulas. Possible comparisons are made with measured data
collected from the “Subang Meteorological Station” (SMS), in Kuala Lumpur and
simulated data obtained from the DOE-2 weather processor to validate the latter in
order to be used in hourly energy simulations.
27
2.5.1 Sky Condition
The earth's atmosphere considerably changes the physical state of solar
radiation and the exterior illuminance which arrives at the surface of the earth.
Different molecules (aerosols absorbed and scattered part of it) and influence of
cloud cover affect the flux of solar radiation. This implies that different types of sky
result from different types of climate and geographical location. The intensity of the
solar radiation varies for different sky conditions, namely clear sky (blue sky),
overcast sky, intermediate overcast sky, intermediated mean sky and intermediate
blue sky. Different methods are being used in predicting different sky conditions.
The most commonly used methods are based on using cloud cover ratio (Muneer,
2000; Ramli Rahim et al, 2004), sunshine duration data (Ramli Rahim et al, 2004)
and calculating the nebulosity index (NI) (Azni Zain-Ahmed et al, 2002). As
reviewed by Muneer (2000), previous studies indicated 70-85% of models are based
on the sunshine duration and 50% are based on the cloud cover.
Relative sunshine duration (S) is the most extensively used weather parameter
for estimating radiation flux. It is defined as the ratio of daily sunshine duration (n)
to maximum possible sunshine duration (no) or day-length.
S = (n) / (no)
(2.14)
The cloud cover ratio (Kcc) emphasises the amount of sky covered with
clouds. Also the definition of cloud ratio is taken as proportion of the diffused
irradiance (Idiff,h) to global irradiance (IGh) (Ramli Rahim et al, 2004). A similar
approach is used in daylight experiments as the ratio of the diffuse illuminance to the
global illuminance is adopted as cloud ratio. Theoretically the range of cloud ratio is
considered as 0-10, representing 0 cloud ratio indicates a clear sky and cloud ratio 10
indicates an overcast sky. A similar bench mark is created in daylight experiments,
where cloudiness factor ranges from 0 for overcast sky to 1.0 for clear sky.
Kcc = (Idiff,h) / (IGh)
(2.15)
28
The Nebulosity Index NI is calculated using solar geometry, diffused
radiation (Idiff,h), global radiation (IGh) and diffused illuminance (Azni Zain-Ahmed et
al, 2002).
NI = {1-Idiff, h / IGh}
(2.16)
(1-CR)
The cloud ratio CR can be calculated using:
CR = Ėdiff,cl / { Ėdiff,cl + exp(-4mAr) sinβ}
(2.17)
Where, Ėdiff,cl is clear sky diffuse illuminance given by:
Ėdiff,cl = 0.0065 + (0.255-0.138 sinβ) sinβ
(2.18)
m = [sinβ +0.50572 exp {-1.6364 In (β+6.07995)}]-1
(2.19)
Ar = {55.4729+m [3.0312+m {-0.6329+m (0.091-0.00512m)}]}-1 (2.20)
Where ‘Ar’ is the Rayleigh scattering coefficient, ‘m’ is the optical air mass
and β is the solar altitude.
Azni Zain-Ahmed et al (2002) used the nebulosity index (NI) to determine
sky conditions and to calculate the irradiances in Malaysia. According to different
NI values, the sky conditions are categorized as shown in table 2.2 below. Based on
the occurrences of sky types, the study concluded that the Malaysian sky is
predominantly an intermediate sky. This was justified by the calculated mean NI
value for Malaysian as 0.52, which lies between the range of intermediate sky 0.20
and 0.70. The definition of intermediate implies that the sky is neither clear nor
overcast (Azni Zain-Ahmed et al, 2002).
The ratio between irradiance (W/m2) and illuminance (lux) predicts the
luminous efficacy (lm/W) which differs depending on the sky type. The respective
values of beam, diffuse and global efficacies were calculated using equations (2.22),
29
(2.23) and (2.24) respectively for measured and empirical model (Muneer, 1997;
Littlefair, 1988; Azni Zain-Ahmed et al, 2002).
Table 2.2: Different Sky types according to Nebulosity Index, Subang Jaya
Malaysia. Source: Azni Zain-Ahmed et al. (2002)
Type of Sky
Nebulosity Index (NI)
Frequency (%)
Overcast Sky
0.00<0.05
14.0
Intermediate overcast
0.05<0.20
2.3
Intermediate mean
0.20<0.70
66.0
Intermediate Blue
0.70<0.95
17.3
Blue / Clear Sky
0.95<1.00
0
The calculated annual average values of global diffused and beam efficacy
for Subang area are 112 lm/W, 120 lm/W and 104 lm/W respectively (Azni ZainAhmed et al, 2002). Further, the mean global efficacy based on measured irradiance
and illuminance values for Shah Alam and Bangi (in Kuala Lumpur Malaysia)
indicated 119+ 2% lm/W and 133 + 2% lm/W respectively.
K (luminous efficacy) =
Beam luminous efficacy (KB) =
Diffuse luminous efficacy (KD) =
Global luminous efficacy (KG) =
Illuminance
Irradiance
Illuminance from sunlight (Eo,sun)
Beam Irradiance (Ibh)
Diffuse Illuminance (Eo,sky)
Diffuse Irradiance (Idiff, h)
Global Illuminance (Eo)
Global Irradiance (IG)
(lm/W) (2.21)
(lm/W) (2.22)
(lm/W) (2.23)
(lm/W) (2.24)
However, in broad terms, sky conditions can be divided into three types
(CIE- International Illumination Commission); clear sky, overcast sky and
30
intermediate sky. As reviewed by Hamdan (1996), characteristics of hot and humid
equatorial climates like in Malaysia vary significantly through out the day. This
condition is mainly due to the formation of clouds creating sky patches and resulting
in obstruction of the sun. Therefore, the solar radiation penetration is not constant
and the intensity of the solar radiation from the sky vault is a combination of direct
sun, clear sky portion and from the cloudy portion. However, Azni Zain-Ahmed et al
(2002) concluded by evaluating long term meteorological data, that impact of direct
solar radiation is predominant and global exterior illuminances may exceed 100,000
lux during brightest months and 60,000 lux under cloudy sky conditions in Malaysia.
2.5.2 Solar Radiation Analysis
Comparison between the SMS measured and the DOE weather file (DOE.wf)
data indicates a closer and a similar pattern for horizontal solar radiation for the
location Kuala Lumpur. However, the DOE weather data indicated higher solar
radiation intensity on 21 March, 24 September and 21 December during the peak
hours (11:00 -15:00 hours) (table 2.3). The DOE.wf data indicated 22%, 20% and
5% of mean daily solar radiation value increment on respective days (21 March, 24
September & 21 December) compared to the SMS data. On 22 June measured data
at the SMS indicated a higher value. The measurements indicated a 10% increase in
mean daily solar radiation for June 22, compared to the SMS data.
The measured maximum hourly horizontal solar radiation value reported for
21 March was 927 W/m2 at 12:00 noon, while simulated value indicated a maximum
value of 967 W/m2 at 13:00 hour. On 22 June, maximum value reported at the SMS
is about 713 W/m2 at 12:00 noon and 586 W/m2 was indicated by the DOE.wf at
14:00 hour. The maximum value on 24 September was obtained at 11:00 and 13:00
hours which indicated 855 W/m2 and 989 W/m2 for the SMS and the DOE.wf
respectively. December 22 received maximum values of 738 W/m2 and 863 W/m2
for the SMS and the DOE.wf respectively. Hence, it can be concluded that
Malaysian skies radiate high solar radiation intensity (table 2.3).
31
Table 2.3: Comparison of measured SMS and DOE-weather file data for hourly
horizontal solar radiation for Kuala Lumpur (2001) (Latitude: 3.120, Longitude:
+101.60 & Time zone: +7)
Hour
7
8
9
10
11
12
13
14
15
16
17
18
19
21-Mar
SMS
KL
measure DOE.wf
W/m2
W/m2
63.88
0
277.72 148.144
527.67 305.744
624.88
409.76
891.49 734.416
927.59 955.056
344.38 967.664
372.15 939.296
505.46
788
566.55 690.288
241.62 475.952
72.21
220.64
0
18.912
22-Jun
SMS
KL
measure DOE.wf
W/m2
W/m2
36.10
0
244.40
226.94
352.71
293.13
441.58
409.76
405.48
532.68
713.75
447.58
649.87
387.69
449.91
586.27
394.37
485.40
336.04
264.76
163.86
138.68
77.76
34.67
0
3.15
24-Sep
SMS
KL
measure DOE.wf
W/m2
W/m2
8.33
0
91.65
75.64
263.84
252.16
461.02
469.64
855.39
614.64
802.62
932.99
722.08
989.72
441.58
806.91
211.07
412.91
488.79
403.45
86.09
286.83
30.55
148.14
0
0
21-Dec
SMS
KL
measure DOE.wf
W/m2
W/m2
8.33
0
63.88
148.14
241.62
371.93
413.81
576.81
738.74
721.80
605.44
863.64
822.06
535.84
608.21
561.05
380.48
375.08
341.60
302.59
247.17
195.42
0
53.58
0
9.45
Horizontal Solar radiation data from both weather files were also evaluated
by employing a statistical analysis. The ‘mean bias error’ (MBE) and the ‘root mean
square error’ (RMSE) are most commonly used indicators in examining the model’s
performances (Muneer, 1998; Robledo et.al, 2001). The MBE indicates whether the
trend under predict or over predict its modelled values. The result is expressed as a
percentage. As reviewed by Muneer (1998) on the work done by Drummond (1965)
and Coulson (1975), suggests that accuracies of the order of 2-3% (MBE) are
acceptable for daily summations of radiation and hourly summations may have error
of 5%- 11% (MBE) at lower solar elevations.
MBE =
RMSE =
Σ (estimated value – measured value)
No.
of measurements
Σ (estimated value – measured value) 2
No.
of measurements
(W h/m2) (2.25)
(W h/m2) (2.26)
32
Table.2.4 shows the results of MBE and RMSE calculated for data measured
at the Subang Meteorological Station (SMS) and estimated values obtained from the
DOE weather file. The results yield MBE and RMSE in the range 0.4%- 6.8% and
1.5%- 23.7% respectively. In both cases, 28 January, 24 July and 28 August indicate
higher values. Values on January and July suggests that the DOE.wf values over
predicts than the SMS data, while on August the DOE.wf under predicts the values
compared to the SMS data. However, in other months, the MBE values ranged
between 0.4% and 1.9% which is within the acceptable range. In view of the above
accuracy criterion, it is assumed that the DOE.wf data provide relatively similar
climatic conditions of hot and humid climates.
Table 2.4: Monthly mean global horizontal solar radiations (W/m2) and MBE &
RMSE values for SMS and DOE.wf (Kuala Lumpur)
Day
DOE.wf
Subang MS (SMS)
MBE
RMSE
Month
Mean estimated
value(W/m2)
Mean measured
value(W/m2)
%
%
28-Jan
23-Feb
21-Mar
16-Apr
21-May
22-Jun
24-Jul
28-Aug
24-Sep
20-Oct
22-Nov
21-Dec
5995.1
5226.0
6653.9
4103.9
4816.3
3810.8
5159.8
2036.2
5393.1
4144.9
3621.6
4705.9
4015.9
4943.5
5415.6
4449.1
5235.1
4265.8
2832.8
4335.3
4454.7
5240.6
4193.6
4471.3
4.1
0.5
1.9
-0.6
-0.7
-0.9
6.8
-4.4
1.9
-1.7
-1.1
0.4
14.2
1.6
6.6
2.2
2.3
3.1
23.7
15.3
6.4
6.0
3.9
1.5
33
2
Global Horizontal Solar Radiation (W/m )
1200
1000
800
600
400
200
32
1
32 7
1
32 9
11
32 1
11
32 3
11
32 5
11
32 7
11
62 9
2
62 7
2
62 9
21
62 1
21
62 3
21
62 5
21
62 7
21
92 9
4
92 7
4
92 9
41
92 1
41
92 3
41
92 5
41
92 7
4
12 19
21
12 7
2
12 1 9
21
12 11
21
12 13
21
12 15
21
12 17
21
19
0
Month/ Day/ Hour
Measured-subang MS
DOE.WF-KL
Figure 2.1: Comparison of global horizontal solar radiation between SMS
(measured) and DOE-wf (simulated) for Kuala Lumpur- 21 March, 22 June, 24
September and 21 December
Direct normal solar radiations (In) and diffuse radiations (Idiff) are obtained for
clear sky conditions. The required variables and measurements are as follows; the
solar constant (Isc), clearness number for the hour (Cn), solar extinction coefficient
(Sec) and sky diffusive factor (Sdf). If the solar tapes are available, measured data
were considered in order to derive the direct normal radiation and diffuse radiation.
If the simulation uses a non-solar weather tape, the following methods are used to
calculate the direct and diffuse solar radiations.
Direct normal
Solar radiation
Clear day direct
normal solar
radiation
=
X
Cloud cover
(2.27)
And,
Diffuse
horizontal solar
radiation from
sky
=
Clear day diffuse
horizontal solar
radiation
X
Cloud cover
(2.28)
34
Table 2.5: Hourly direct normal solar radiations (x cloud cover) and diffuse
horizontal solar radiation (x cloud cover) - DOE. wf. (Kuala Lumpur); (W/m2)
21-Mar
Hour
8
9
10
11
12
13
14
15
16
17
18
19
Direct
(W/m2)
368.78
337.26
277.38
510.62
715.50
690.29
674.53
583.12
583.12
475.95
302.59
110.32
Diffuce
(W/m2)
38.77
126.08
206.46
283.05
258.15
278.95
295.97
295.66
295.03
254.68
154.13
13.87
22-Jun
Direct
(W/m2)
472.80
151.30
144.99
249.01
173.36
91.41
308.90
330.96
189.12
107.17
44.13
0.00
24-Sep
Diffuce
(W/m2)
78.17
213.08
307.00
323.08
288.09
302.28
311.73
226.00
146.25
92.98
25.85
3.15
Direct
(W/m2)
75.65
132.38
223.79
296.29
709.20
724.96
450.74
132.38
201.73
223.79
220.64
0.00
21-Dec
Diffuce
(W/m2)
48.54
174.31
295.97
344.51
233.88
270.44
387.07
306.06
277.06
196.37
114.10
0.00
Direct
(W/m2)
460.19
665.07
683.98
665.07
775.39
378.24
378.24
230.10
75.65
144.99
50.43
59.89
Diffuce
(W/m2)
16.71
40.35
114.10
185.65
181.24
198.26
242.70
206.46
259.41
141.52
46.33
8.83
According to table 2.6, on 21 March, 24 September and 21 December, the
impact of the direct normal solar radiation is high except on 22 June, where the
diffused component is high. The ratio between diffuse to direct solar radiations is
calculated. A lower ratio on 21 March and 21 December indicates a clear sky on
above days and higher ratio values suggest a cloudy sky on 22 June and 24
September. Thus, this implies that the correspondence characteristic of partly clear
and partly cloudy sky is evident.
Table 2.6: Percentage of direct normal solar radiation and diffuse horizontal solar
radiation, DOE.wf for Kuala Lumpur (2001)
21-March
%
Ratio
22-June
24-September
21-December
Direct
(W/m2)
Diffuce
(W/m2)
Direct
(W/m2)
Diffuce
(W/m2)
Direct
(W/m2)
Diffuce
(W/m2)
Direct
(W/m2)
Diffuce
(W/m2)
69%
30.70%
53%
55%
56%
43.80%
73%
26%
0.44
1.02
0.78
0.36
The hourly total solar radiation on vertical surface were simulated and shown
in fig 2.2 to fig 2.5. The data indicates, on 21 March and 24 September the west
surface received higher solar radiation than the east oriented surface. On 21 March
east façade obtained a maximum of over 500 W/m2, while the west received over
700W/m2 on the same day (figure 2.2). When compared to the north and south,
35
impact of solar radiation on the east and west surfaces are higher. On 24 September
maximum intensity was recorded on the west oriented vertical plane which is about
450 W/m2 and on the east it is about 350W/m2 (figure 2.4).
800
600
2
Solar Radiation (W/m )
700
500
400
300
200
100
0
6
7
8
9
10
North
Figure 2.2:
21 March
11
12
13
Hour
14
East
15
16
17
South
18
19
20
West
Hourly total solar radiations (direct & diffused) on vertical surface on
600
Solar Radiation (W/m2)
500
400
300
200
100
0
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
Hour
North
Figure 2.3:
on 22 June
East
South
West
Hourly total solar radiations (direct & diffused) on vertical surface
36
On 22 June, the north and east surface received a considerably higher amount
of radiation. On this day, the east obtained solar radiation intensity of about 450
W/m2 and the north and west indicated a maximum intensity of just about 300 W/m2
(figure 2.3).
500
450
2
Solar Radiation (W/m )
400
350
300
250
200
150
100
50
0
6
7
8
9
10
11
North
12
13
Hour
14
East
15
16
17
South
18
19
20
West
Figure 2.4: Hourly total solar radiations (direct & diffused) on vertical surface
on 24 September
700
2
Solar Radiation (W/m )
600
500
400
300
200
100
0
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
Hour
North
East
South
West
Figure 2.5: Hourly total solar radiations (direct & diffused) on vertical surface on
21 December
During 21 December the impact of solar radiation were strong on the east and
the south surfaces. As shown in figure 2.5, the east surface received about 450 W/m2
37
while the west surface received just about 300 W/m2. The south façade also received
considerable amount of solar radiation of about 300 W/m2.
2.5.3 Outdoor Design Temperature Analysis
Hourly outdoor temperatures were obtained in dry-bulb (DBT) and wet-bulb
(WBT) scale (figure 2.6 & 2.7). The highest temperature in DBT (36.1 0C) was
recorded on 22 June and in WBT (26.1 0C) in 21 March. Monthly mean values of
both DBT and WBT were shown in figure 2.8 and 2.9. A comparison between the
SMS data and the DOE.wf data indicated that the SMS data had a maximum of 1.3
0
C differences for WBT on the month of January and a range between 0.08 0C to
0.86 0C differences on other months except on February than the DOE.wf data. In
February, the DOE.wf data measured a 0.2 0C temperature difference than the SMS
DBT-oC
data.
37
36
35
34
33
32
31
30
29
28
27
26
25
24
23
22
21
20
Outdoor design temperature
DBT 330C(MS1525:2001)
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24
Hour
21-Mar
22-Jun
24-Sep
21-Dec
Figure 2.6: Hourly variations of dry bulb temperature (DBT) for 21 March, 22
June, 24 September and 21 December, DOE. wf. for Kuala Lumpur
38
30
29
Outdoor design temperature
0C
WBT 27.2 (MS 1525:2001)
28
27
WBT- oC
26
25
24
23
22
21
20
19
18
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24
Hour
21-Mar
22-Jun
24-Sep
21-Dec
Figure 2.7: Hourly variations of wet bulb temperature (WBT) for 21 March, 22
June, 24 September and 21 December, DOE. wf. for Kuala Lumpur
The SMS and DOE.wf measurements difference for DBT showed a range
between 0.04 0C to 1.04 0C. The month of April indicated a 1.04 0C difference
between DOE.wf and SMS measurements. Comparing the monthly mean readings
of DBT, the DOE.wf data emphasized a higher value on April, May, July, August,
0
Mean Drybulb Temperature ( C)
September, October and November than any other months.
30
28
26
24
22
20
18
16
14
12
10
8
6
4
2
0
-2
Jan
Feb
Mar
Apr
May
Jun
Jul
Aug
Sep
Oct
Nov
Dec
Months
Measured-Subang MS
Figure 2.8:
DOE.WF-KL
Temperature Difference
Comparison of monthly mean DBT (0C) data from SMS and DOE.wf
Mean Wetbulb Temperature (0C)
39
28
26
24
22
20
18
16
14
12
10
8
6
4
2
0
-2
Jan
Feb
Mar
Apr
May
Jun
Jul
Aug
Sep
Oct
Nov
Dec
Months
Measured-Subang MS
Figure 2.9:
DOE.WF-KL
Temperature Difference
Comparison of monthly mean WBT (0C) data from SMS and DOE.wf
The temperature to which air must be cooled to become saturated at constant
pressure is called the dew-point temperature (Td, also DewPT). The monthly mean
dew point temperatures from both weather data were plotted as shown in fig. 2.10.
The differences ranged between 1.7 0C and 0.06 0C. The maximum difference of 1.7
0
C was emphasized during the month of January and on other months the difference
Dew Point Temperature (0C)
was less than 1 0C.
26
24
22
20
18
16
14
12
10
8
6
4
2
0
-2
-4
Jan
Feb
Mar
Apr
May
Jun
Jul
Aug
Sep
Oct
Nov
Dec
Months
Measured-Subang MS
DOE.WF-KL
Temperature Difference
Figure 2.10:
Monthly variation of Dew Point Temperatures (0C) data from
SMS and DOE.wf
40
Table 2.7 shows the monthly mean values of the DBT, WBT and dew-point
temperatures and correspondence mean bias error (MBE) values. The MBE for DBT
ranged between 0.17% and 3.65%; for WBT indicated the range between 0.31% and
5.31% and DewPT ranged between 0.00% and 7.41%. The statistics indicated that
all the values were within an acceptable error range (less than 11%). The MBE value
for DBT also suggests more accuracy with the measured temperature.
Table 2.7: Monthly mean values of DBT, WBT and DewPT and correspondence
Mean Bias Error (MBE) values
Month
Jan
Feb
Mar
Apr
May
Jun
Jul
Aug
Sep
Oct
Nov
Dec
Dry-bulb Temperature
(oC)
DOE.
MBE
SMS
wf
%
26.90 26.94
0.17
27.20 27.22
0.08
27.30 27.56
0.94
28.60 27.56
-3.65
27.80 27.39
-1.48
28.10 28.17
0.24
27.80 27.17
-2.28
27.50 27.33
-0.61
27.20 26.89
-1.14
27.00 26.67
-1.23
27.10 26.28
-3.03
27.00 27.06
0.21
Wet-bulb
Temperature (oC)
DOE. MBE
SMS
wf
%
24.70 23.39 -5.31
24.30 24.50 0.82
24.80 24.72 -0.31
25.30 24.94 -1.41
25.10 24.83 -1.06
24.80 23.94 -3.45
24.40 23.89 -2.09
24.50 23.94 -2.27
24.40 24.00 -1.64
24.60 24.17 -1.76
24.70 24.33 -1.48
24.40 24.17 -0.96
Dew point
Temperature (oC)
DOE. MBE
SMS
wf
%
23.70 21.94 -7.41
23.00 23.56 2.42
23.80 23.44 -1.49
24.00 24.06 0.23
24.00 24.00 0.00
23.30 22.33 -4.15
22.90 22.67 -1.02
23.20 22.72 -2.06
23.30 22.94 -1.53
23.50 23.22 -1.18
23.70 23.61 -0.38
23.40 23.06 -1.47
2.5.4 Exterior Illuminance Analysis
It is reported by Azni Zain-Ahmed et al (2002) and Hamdan (1996) that there
is no long term daylight data for Malaysian climate. In this study the daylight hourly
availability has been simulated for Malaysian conditions using daylight modelling
techniques based on empirical and measured solar irradiance, using the DOE-2
simulation engine. Then, the data were compared with findings of Azni Zain Ahmed
et al (2002) for validation. Current hour exterior horizontal illuminance in the DOE
program were calculated by using current hour sun position, cloud cover and
measured or calculated horizontal solar radiation. The daylight calculations were
performed for standard clear and overcast sky conditions for a series of 20 different
41
solar altitudes and azimuth angles covering the annual range of sun positions at
correspondence location.
The calculated hourly exterior illuminances were obtained from three
different sources; illuminances from clear part of the sky, overcast part of the sky and
from direct sun. The exterior illuminance for 21 March, 22 June, 24 September and
Ext: Illuminance (Lux)
21 December were shown in figure 2.11 to 2.14.
130,000
120,000
110,000
100,000
90,000
80,000
70,000
60,000
50,000
40,000
30,000
20,000
10,000
0
8
9
10
11
12
13
14
15
16
17
18
19
Hour
Clear sky
Overcast sky
Direct Sun
Total Illuminance
Figure 2.11: Exterior horizontal illuminance for 21 March, DOE.wf data for
Kuala Lumpur
The direct sun component is the main contributor on the exterior illuminance
for 21 March, 24 September and 21 December. Contribution of the clear sky and the
overcast sky create the diffuse component of the illumination. Illuminance from
overcast part of the sky was dominant during 22 June. The respective total exterior
illuminance for each respective day was found to be; 114,346 lux, 68,412 lux,
116,089 lux and 100,143 lux as illustrated in table.2.9 and fig 2.15. Table 2.9 shows
the monthly maximum contribution of each sky type (clear and overcast) and direct
sun on the exterior illuminance.
42
80,000
Exterior Illuminance (lux)
70,000
60,000
50,000
40,000
30,000
20,000
10,000
0
8
9
10
11
12
13
14
15
16
17
18
19
Hour
Clear sky
Figure 2.12:
Lumpur
Overcast sky
Direct sun
Total Illuminance
Exterior horizontal illuminance for 22 June, DOE.wf data for Kuala
140,000
Exterior Illuminance (lux)
120,000
100,000
80,000
60,000
40,000
20,000
0
8
9
10
Clear sky
11
12
13
14
Hour
Overcast sky Direct sun
15
16
17
18
Total Illuminance
Figure 2.13: Exterior horizontal illuminance for 24 September, DOE.wf data for
Kuala Lumpur
43
110,000
Exterior Illuminance (lux)
100,000
90,000
80,000
70,000
60,000
50,000
40,000
30,000
20,000
10,000
0
8
9
10
11
12
13
14
15
16
17
18
19
Hour
Clear sky
Overcast sky
Direct sun
Total Illuminance
Figure 2.14: Exterior horizontal illuminance for 21 December, DOE.wf data for
Kuala Lumpur
The calculated results showed that mean average total diffuse exterior
illuminance (clear + overcast sky) as 67,927 lux and the mean average total exterior
illuminance (diffuse + direct) as 163,885 lux. These values showed close
relationship with measured values for total illuminance which exceeds 100,000 lux in
Shah Alam (which is closer to Subang MS) and 140,000 lux in Bangi (Azni ZainAhmed et al, 2002).
A set of hourly global irradiance and illuminance data were obtained for each
month simulated for Kuala Lumpur from the DOE.wf. The calculated mean global
luminous efficacy indicated a value of 118 lm/W (figure 2.16) which is very close to
the established value by measured data for Shah Alam.
44
Exterior Illuminance (lux)
140,000
120,000
100,000
80,000
60,000
40,000
20,000
0
8
9
10
11
21-Mar
12
13
14
15
Hour
22-Jun 24-Sep
16
17
18
19
21-Dec
Figure 2.15: Total exterior horizontal illuminance, DOE.wf data for Kuala Lumpur
140,000
Global Illuminance (Lux)
120,000
y = 118.4x - 338.57
2
R = 0.9979
100,000
80,000
60,000
40,000
20,000
0
0
200
400
600
800
1000
1200
2
Global Irradiance (W/m )
Figure 2.16: Calculated global luminous efficacies (lm/W) from DOE.wf data for
Kuala Lumpur
45
Table 2.8: Horizontal exterior diffuse illuminance values (clear sky & overcast
sky) on 21 March, 22 June, 24 September and 21 December, DOE.wf (Kuala
Lumpur)
Time
(Hour)
8.00
9.00
10.00
11.00
12.00
13.00
14.00
15.00
16.00
17.00
18.00
19.00
Horizontal exterior diffused illuminance from sky
(Lux)
21-Mar
22-Jun
24-Sep
21-Dec
4874.28
15806.44
25888.56
35508
32376.84
34980.76
37132.76
37078.96
37014.4
31957.2
19314.2
1743.12
9791.6
26717.08
38499.28
40511.4
36153.6
37907.48
39091.08
28363.36
18345.8
11642.32
3228
387.36
6090.16
21875.08
37122
43212.16
29353.28
33915.52
48570.64
38402.44
34744.04
24618.88
14300.04
-
2087.44
5046.44
14321.56
23263.12
22746.64
24887.88
30418.52
25888.56
32527.48
17743.24
5799.64
1097.52
Table 2.9: Hourly maximum global exterior illuminance for 21 March, 22 June, 24
September and 21 December, DOE.wf. (Kuala Lumpur)
Day/
Month
21-Mar
22-Jun
24-Sep
21-Dec
GLOBAL EXTERNAL ILLUMINANCE
(hourly maximum- Lux) DOE.wf
Clear
Overcast Diffused
Direct
Sky
Sky
Total
Sun
Total
(Cl.sky+
Sky
Sky
Ove.sky)
Illuminance
17,754
32,495
79,484
114,346
37,132
30,386
14,439
29,321
68,412
40,511
6,068
42,502
82,174
116,089
48,570
4,067
28,460
77,396
100,143
32,527
Diffused Direct
Illuminance
%
32.47
59.22
41.84
32.48
%
69.51
42.86
70.79
77.29
Table 2.10 and figure 2.17 show the monthly maximum exterior illuminance
obtained by each part of sky conditions. Months of January and November indicated
the lowest direct sunlight illuminance, while the maximum amount was reported on
April. Generally, the maximum sunlight mean value was about 95,000 lux.
46
Exterior global illuminance (Lux)
120,000
100,000
80,000
60,000
40,000
20,000
0
Jan Feb Mar Apr May Jun
Jul Aug Sep Oct Nov Dec
Month
Clear Sky
Overcast Sky
Direct Sun
Figure 2.17: Monthly maximum exterior illuminance values from clear sky,
overcast sky and direct sun, DOE.wf (Kuala Lumpur)
The overcast sky had an average maximum value of about 46,000 lux and the
monthly maximum was indicated on June and July. During this time, the sun
location was farthest from the equator. The lowest illuminance from the overcast sky
was indicated on March. Under clear sky conditions, the maximum illuminance was
received on January and July, which is about 35,000 lux. The lowest illuminance
was indicated on August, October, November and December.
Table 2.10: Monthly maximum exterior illuminance values from clear sky,
overcast sky and direct sun, DOE.wf, (Kuala Lumpur)
GLOBAL EXTERNAL ILLUMINANCE (Monthly maximum)
Month
Clear Sky (lux)
Overcast Sky (lux)
Direct Sun (lux)
January
February
March
April
May
June
July
August
September
October
November
December
mean average
36,423
20,487
22,166
14,881
19,185
31,989
35,669
7,016
14,375
6,703
6,833
7,177
21,563
47,893
49,055
39,801
51,723
48,248
52,928
52,670
49,119
42,502
46,924
47,796
50,238
46,365
88,544
109,451
99,465
105,297
100,412
99,777
94,344
100,154
101,187
97,733
82,465
93,128
95,958
47
The annual contribution of mean average values of the diffused illuminance
(clear sky + overcast sky) and direct sun illuminance showed 41% and 58%
respectively compared to the mean average total illuminance value. The illuminance
from the overcast sky consists of 68% of the diffuse illuminance. However,
respective percentages of each illuminance component were evaluated as 13% from
clear sky, 28% from overcast sky and 58% from direct sun. This implies that impact
of direct sun on exterior illuminance is predominant.
2.6 Summary
The distinct difference between heat and light of solar spectrum were
discussed. A brief outline of the solar geometry, sun’s position related to altitude
and azimuth angles, factors affecting on the distribution of solar radiation
components were also discussed. Further, a brief review of different models and
commonly used procedures for solar radiation calculation method were also
presented.
Weather data from two different sources for the same location were analysed
to validate their compatibility to be used in energy calculations. Comparisons were
carried out on solar radiation, out door temperature and exterior global illuminance
with measured data and simulated DOE wf data for 2001, as a representative year. A
statistical evaluation was carried out to determine the tendency of simulated data
compared to measured data. The low MBE value range between 0.4% and 1.9%
revealed that solar radiation data from the DOE weather processor presented
relatively similar to measured data. The predicted ratio between diffuse and direct
solar radiation indicated combination of clear and cloudy sky conditions. This was
evident on the illuminance values obtained on 21 March, 22 June, 24 September and
21 December. For example, diffuse to direct radiation ratio on 22 June indicated a
higher ratio than other months, thus predicted a low exterior illuminance level. The
correspondence exterior illuminance values established with the measured data were
determined on the availability of the solar radiation. Therefore, based on these
assumptions, resultant interior illuminance will largely depend on the corresponding
48
outdoor illuminances. The calculated global luminous efficacy also has been
confirmed by the measured data.
The WBT, DBT and DewPT were statistically evaluated and the low MBE
values confirmed the accuracy of the calculated data with the measured data.
Review also revealed that solar intensity and the natural-light availability in
Malaysian sky was very high. The high solar radiation conditions and natural-light
availability may well influence on the building internal thermal, visual performances
and on the energy consumption. With this background, the problem of the impact of
solar radiation and daylight on building energy use were discussed and appropriate
solutions were proposed for further analysis in chapter 3 and 4.
Although the DOE weather processor was developed based on monthly data
and on calculation for clear sky conditions, the comparison of results indicated a
similar atmospheric and solar radiation data to the existing conditions of a hot and
humid climate. Therefore assumptions are made for the following:
o
The characteristic of sky is of a clear sky condition.
o
Impact of the direct solar radiation is dominants in most months
o
High daylight availability
Thereby, it is assumed that using the DOE weather processor data may
provide relevant climatic data for accurate solar radiation, daylight and energy
calculations which represents the hot and humid climates like in Malaysia.
CHAPTER 3
ENERGY USE IN HIGH-RISE OFFICE BUILDINGS, HEAT GAIN AND
SOLAR SHADING
This chapter is divided into three sections. The first section reviews the
energy scenario and the building energy consumption in Malaysian context. This is
to get an overall view on the present development in energy efficiency measures in
Malaysia. It further discuses building design considerations to achieve energy
efficiency in buildings and the factors influencing on the energy consumption in
high-rise office buildings to determine appropriate building configuration for the
experiment. Related review on high-rise office buildings and energy related issues in
Malaysia were derived from secondary data obtained from three forms of sources.
The first review was from the survey conducted under the ASEAN-USAID building
energy conservation project in 1992 (Loewen, et al, 1992). The survey comprised
two hundred (200) numbers of commercial buildings in South East Asian region
including twenty six (26) numbers of office buildings in Malaysia. Details obtained
from this survey were summarized in Appendix C1. The second source of
information was obtained from survey conducted by Harrison et al (1998) on
intelligent buildings in South East Asia. The survey was carried out on fifteen (15)
office buildings, including two (2) office buildings from Malaysia. Summary of the
buildings and data obtained from the survey were presented in Appendix C2. The
term intelligent building is used to determine the intelligent building infrastructure
that serves effective organizational performances. The third form of information was
obtained from previous research work carried out on this field by various researches
and publications.
50
The second section reviews the modes of heat transmission and different
types of heat transmission in buildings. This is mainly to understand the variables
that affect on thermal performance of a building. Finally, third section discuses the
shading device with the aspect of manipulating the solar radiation penetration into
the building. Different shading devices are analyzed to understand the implication
and their basic functions as a solar radiation control device. Major factors affecting
the solar energy transmittance are also discussed. Aspects in determining the
effectiveness of the shading are presented in order to find a suitable energy efficient
shading strategy.
3.1 Energy Consumption Pattern in Malaysia
Energy conservation and energy efficiency has been a great concern in
Malaysia after the oil crisis in year1980 (Ramatha, 1994). Statistics from National
energy balance report for the year 2002 shows that primary energy supplies and final
energy demand had rapid growth between year 1990 and 2002 compared to the
growth from year 1980 to 1990. The energy demand increased by about two times in
year 1990 compared to 1980, while the increase in year 2002 was about three times
than in year 1990. The growth in energy supply and demand increased tremendously
after the economic crisis in 1997-1998 periods.
The commercial and residential sectors in Malaysia consumed about 29% and
20% of the total electricity usage for the year 2002 (MECM, 2002). This was about
7.5% increment for both sectors compared to the electricity consumption for the year
2001. The industrial sector consumed the highest amount of electricity energy which
was about 51% of total electricity usage. The total electricity consumption in year
2001 recorded 63,043 GWh and 66,991.4 GWh in 2002, which was about 6.3%
growth. Further, the annual growth rate for electricity demand has increased to 5.8%
in year 2002 from 4.5% in year 2001. The growth in electrical demand was due to
the economic recovery in the industrial sector and in commercial sector. The total
final commercial energy demand was at 33,290 ktoe (kilotons of oil equivalent) in
year 2002 compared with 31,515 ktoe in year 2001. Thus, it is important to promote
51
energy conservation and efficiency in every energy consumption sectors in the
country in turn to reduce the energy demand in the future.
3.1.1 Energy Consumption in Buildings
Building construction and operation consume vast amount of natural energy
resources and material. They have an impact on the environment by contributing
directly and indirectly to pollution. The use of energy in buildings accounts for
about 40% and 37% of the total primary energy use in European Union countries and
in United States respectively.
Energy studies of commercial buildings in south-east Asia, comprising
Malaysia, Indonesia, Philippines, Singapore and Thailand, were initiated under the
ASEAN-USAID Building Energy Conservation project in 1992. The energy audit
survey was conducted for several building types; offices, hotels, hospitals, retails and
supermarkets. All surveyed data were related to electricity consumption as
electricity is the prime energy scalar and it is exclusively used in ASEAN countries.
The summary of results obtained for office building electricity consumption for each
country is shown in table 3.1. The results showed that the office buildings in this
region have an electricity consumption of 233 kWh/m2/yr on average. Comparison
among the five countries revealed that Malaysia has the highest electricity
consumption of 269 kWh/m2/yr among the office buildings surveyed in year 1992.
In another study by Ramatha (1994), reported that energy consumption for
air-conditioning is about 52% and lighting 42% in office buildings in Malaysia
(based on 1985 statistic). Compared to other South East Asian countries, the energy
consumption for air-conditioning was still high in Malaysia, while Singapore
reported the highest lighting consumption.
52
Table 3.1: Electricity intensity averages for ASEAN countries.
Source: ASEAN-USAID Building Energy Conservation Project Final report
(Loewen et al, 1992)
Country
No. of Buildings
Indonesia
Malaysia
Philippines
Singapore
Thailand
ASEAN
4
26
26
65
7
128
Average Consumption
(kWh/m2/yr)
147
269
235
222
237
233
The breakdown of electric use by component for office building in different
South East Asian countries as calculated using the ASEAM-2 simulation was shown
in table 3.2. According to the results in Malaysian offices, energy consumption for
air-conditioning and fans was about 68.8% and electric lighting was about 23% of
total electricity use.
Table3.2:
Electricity consumption percentages by building components for
ASEAN countries.
Source: ASEAN-USAID Building Energy Conservation Project Final report
(Loewen et al, 1992)
Country
Consumption by Component (%)
Air-condition Fans Lighting Miscellaneous
Indonesia
36.6
43.5
11.8
8.1
Malaysia
60.1
8.7
23.1
8.1
Philippines
45
16.2
22.5
5.6
Singapore
36.6
13.2
24.2
26
ASEAN*
46
15.6
22.5
15.5
DOE-2 Simulation
40
18
23
18
3.1.1.1 Energy Efficient Building Codes and Standards
Few countries in the world have adopted mandatory requirements on energy
conservation for buildings. In broad, evaluating energy performances of buildings
53
can be classified in terms of consumption and building envelop performances
(including its elements; window glazing, shading devices, building materials etc.).
There are number of different standards for calculating thermal transmittance values
(U-values), light and solar transmittance etc. Some examples include, the
ASHRAE/IES 90.1-1999 Standard for building envelop and NFRC standards for
windows (Bulow-Hübe, 2001). In 1997, the commercial building incentive program
(CBIP) suggested an average energy performance for commercial buildings to be at
least 100kWh/m2/yr or better (Larsson, 2003). In year 2001, the department of
standards Malaysia introduced a new code of practice for non-residential buildings
on energy efficiency and use of renewable energy (MS 1525:2001), as a guidance on
the effective use of energy. According to this new code of practice, non-residential
building should comply with an annual energy consumption of less than
135kWh/m2/yr.
Similar standards were formulated considering the heat gain across the
building envelop for cooling dominated buildings. This included the determination
of heat gain through the building envelop using the ‘overall thermal transfer values’
(OTTV) (ASHRAE Standard 90A, 1980; Kannan, 1991; Chan and Chow, 1998;
Chirarattananon and Taveekun, 2004). In Malaysia, the required OTTV of building
envelop for a building with air-conditioned load of above100kW and area exceeding
4000m2 should not be more than 45W/m2 (MS 1525:2001). However, one of the
main constrain in the OTTV calculations is that it only can be used for simple
geometrical shapes. This provides difficulty in calculating complex and circular
building forms.
Apart from architectural and passive design strategies, the MS 1525: 2001
also include descriptions and specifications on the following applications: lighting
requirements, electric power and distribution, air-conditioning and mechanical
ventilation systems and on energy management control systems. Nevertheless it is
important to understand that building energy code usually lays down the bottom line
for energy efficiency.
54
3.1.2 Basic Principles of Energy Efficiency in High-Rise Buildings
Cooling, heating, lighting and ventilation adjustments are made in response to
user needs. The design of a building represents a choice of how these needs and
desires are met. These same design choices also dictate how much non-renewable
energy is necessary to provide these services.
Numerous approaches have been developed to limit the non-renewable
energy needs of commercial and institutional buildings. In general there are three
basic approaches to achieve energy efficiency in buildings, which can be underline
as:
i. Use of architectural form and envelope as elements of environmental control
ii. Development of mechanical and technical system efficiency
iii. Efficient management of systems
First approach encourages for maximum utilization of natural and
environmental conditions prevailing at place where the building is constructed. This
system enables a designer to identify the purpose of a particular type of
environmental control solution and contribution of individual elements. Further,
focus on architectural form and envelope provides a visual picture of the impact of
environmental control alternatives on the users and as well as on built environment.
This study is based on the use of architectural form and envelope as elements of
environmental control in buildings to achieve energy efficiency.
The second approach is to improve the mechanical systems for effective
utilization of energy. The main objectives of using this method are to permit the
most efficient utilization of energy and maximum reduction of energy consuming
loads (Kannan, 1991). Although it is more of a technical aspect, the building
envelopes can be designed to reduce the peak loads. This may result in reducing the
size and cost of the mechanical system.
55
The third approach is managing the building energy utilities by controlling
the runtime and excessive usage. This may be accomplished by manual control or
using technologies such as automatic sensors to response to the interior design
conditions. Management systems can be set and operated according to the time of
the day, seasonal variations and depending on various functional requirements.
However, any system cannot independently provide satisfactory results and
need to be combined at various degrees. To obtain maximum effects, they must be
adopted in coordinated combinations in the stage of planning and design of the
building. Whilst observed from the aspect of energy efficiency and use of
architectural form and envelope, building can be classified into three environmental
control alternatives:
i. Climate rejecting buildings
ii. Climate adapted buildings
iii. Combination of climate adapted and climate rejected buildings
3.1.2.1 Climate Rejecting Building
Climate rejecting buildings can be defined as buildings that use the form and
envelope to reduce climate imposed loads. Thus, the form and envelope options
isolate occupied spaces from the influence of climate. The envelope options include
strategies such as reflective glazing, external shading and additional insulations. The
energy effectiveness of the form is improved by limiting the skin-to-floor area ratio
that contains the smallest volume of a cube like shape. In such buildings the
environmental control strategies are handled by artificial means, such as electric
lighting, air-conditioning and ventilation systems. Therefore, the energy
consumption in climate rejecting buildings is very high and such buildings are also
described as ‘internal load dominated buildings’. The energy needs of a climate
rejecting building can be reduced by both making the form and envelope a better
barrier to climate or by improving the effectiveness of internal systems.
56
Some examples of climate rejecting high-rise buildings in Malaysia are:
LUTH building in Kuala Lumpur and the Komtar tower in Penang (figure 3.1).
The LUTH
Building in
Kuala Lumpur
The KOMTAR
Building in
Penang
Figure 3.1: Examples of climate rejecting high-rise buildings in Malaysia
Source: Voon Fee (1998)
3.1.2.2 Climate Adapted Building
Climate adaptive buildings can be defined as buildings that selectively filter
and balance the positive and negative influences of the climate to provide internal
environmental control. Thus, external climatic energy sources are filtered and
distributed to occupied spaces via the building envelope for end uses such as
lighting, thermal comforts and ventilation. The depth of a climate adapted building
is generally narrow as dictated by the limits of the penetration of natural light and air.
The envelope options of climate adapted buildings include large openings with
appropriate solar shading, light-shelf and appropriate insulations. However, the
building form and envelope configurations largely depend on the location and the
prevailing climatic conditions. In these building types, the energy use pattern is
dominated by the heat gains through the building envelope or the building skin and
such buildings are described as ‘skin-dominated buildings’.
57
One of the best examples in Malaysia is the PWD standard office buildings
design by W.Ivor Shipley, which was only 3 storey high, with a single corridor and
was naturally ventilated (Voon Fee, 1998) (figure 3.2). The design was later adapted
for high-rise buildings, with the use of air-conditioning and additional row of offices
(Abdul Majid, 1996).
Typical floor plan of a PWD office block
Figure 3.2: Example of climate adapted building: Public Works Department
(PWD or JKR) building, Kuala Lumpur.
Source: Voon Fee (1998)
3.1.2.3 Combination of Climate Adapted and Climate Rejected Building
The contradictory design principles of the above two approaches were
combined to the best advantage of both climate adaptive techniques and internal
system technology as environmental control alternative. The environmental control
equipment in a climate adapted building is required for two reasons. First, very few
climates and building configurations will permit the exclusive use of direct climatic
forces to meet all needs of the users. Secondly, climatic energies are typically
transient sources of energy, changing hourly, daily and seasonally. These changes
seldom match with the need of energy in most buildings. For instance, forced
ventilation can cool a building during the periods when natural air is ineffective.
Similarly, reducing solar heat gain may be a better trade off than use of daylight to
reduce artificial lighting in buildings in high solar radiation intensity regions. Thus
choice of environmental control in the climate adapted building can influence the
form and envelop design of the building. Further, the use of environment control
58
equipment in climate adapted building defines the trade offs that must be made to
achieve a successful hybrid solution.
Most buildings design by Ken Yeang can be categorized as combination of
climate adapted and rejected buildings, e.g. 21 storeys high Menara UMNO, 27
storeys high Central Plaza, Menara Mesiniaga and 37 storeys high Budaya Tower
(figure 3.3). Abdul Majid (1996) summarized common architectural features of
climate adapted and rejected combined building into four forms: Buildings
dominated by external solar shading devices, buildings with double layer walls and
external screen walls, building with articulated facades and buildings with
intermediate spaces.
1). Menara Mesiniaga,
Subang Jaya, Kuala Lumpur.
2). Menara UMNO, Penang
Figure 3.3:
Combination of climate adapted and rejected buildings in Malaysia
However, two common methods can be identified in combining the climate
adapted features and climate rejected features:
1) Dividing the building spaces into portions to get the full benefit of the
natural resources and partial benefits. In other words, lift lobbies, toilets, stairwells
were designed to take the full advantage of the natural ventilation and daylight, thus
the occupied spaces to be operated by mechanical means; e.g. Menara Mesiniaga,
Subang Jaya, Kuala Lumpur.
59
2) Designing the building that can be adopted for both conditions. Meaning
that the building is design for air-conditioning but if required it can be naturally
ventilated and day-lit; e.g. Menara UMNO, Penang.
Energy consumption is climate dependent. Any energy efficient strategy
should respond to the prevailing climatic conditions than only complying with the
standards. Another important aspect is that energy reduction strategy should
consider comfort of the user as well. Therefore, reducing the energy consumption in
buildings is far more challenging task than just fulfilling the proposed standards.
These standards have been implemented for mechanical system controls,
management systems and architectural design strategies to achieve the target energy
consumption levels. However, there are more potential to develop more integrating
solutions such as minimizing solar heat gains and maximizing daylight utilization
through climate responsive design strategies. The review on the selected existing
buildings also suggested that space loads and lighting loads are the main contributors
on high energy consumption in buildings. Thus, the following section discusses the
principles and the factors influencing high energy consumption in buildings.
3.1.3 Review Related Research on High-Rise Office Building
The main aim of this review is to understand the overall architectural design
features of the existing high-rise office buildings in tropical climatic regions. From
the literature review it was found that there are five main architectural design
influences on high-rise configuration: building form and orientation, core plan, floor
plan, building envelope and articulated spaces (Kannan, 1991; Yeang, 1994;
Hamdan, 1996; Abdul Majid, 1996; Hassan, KAKU 1996; Azni Zain-Ahmed, 2002).
60
3.1.3.1 High-Rise Building Form and Orientation
Physically building configuration can be defined as the scale and the shape of
the form. This can be further elaborated as the nature, size and location of structural
and non-structural elements of a building. These include elements such as walls,
service core, floor, columns, partitions and the perforation of exterior wall for light
and air. Articulation of the physical elements and components according to internal
spatial requirement create the essential built form of the high-rise building structure.
Markus (1980) developed a theoretical method to determine the optimum size
for thermal performance by using surface area to volume ratio of a building. The
finding suggested two important parameters: optimum form that gives the lowest
value of ‘surface area to volume ratio’ (the cube form) and lowest thermal
performance was obtained for higher surface to volume ratio. These findings were
based on thermal heat losses, which is relevant to buildings in temperate climates
where the building heat loses are critical during the winter. In hot and humid
climates like Malaysia, the relationship between the shape of the building and solar
heat gains are more critical. This implies that minimizing the surface exposed to the
sun is the main design criterion.
a)
Building Form, Width, Length and Height
Yeang (1994) established the high-rise building form according to the
influence from the climate. The optimum building forms for each climatic zone were
given as ratio of the length and the width of the building, as shown in figure 3.4. The
optimum building form for hot and humid tropical climate conditions is 1:3 ratios,
where the length is three times the width. The preferred orientation is to face the
longitudinal façade towards the north and south. Yet, the method does not determine
the height of the building as well as on the amount of energy consumed.
Review suggests that there are no definite conclusions being made in specific
terms of height of high-rise building with energy consumption. Influence of high-
61
rise building form on its energy use was studied by Kannan (1991). His study was
limited to three foot print ratios and two window options. The results were compared
with the air-condition loads for various orientations depending on the foot print ratio.
The study showed square plan option with 1:1 ratio and windows facing the north
and south had the lowest cooling load and for the same orientation with 4:1 ratio and
two window options indicated higher value. Building arranged longitudinally along
north and south had 10% more energy consumption than building arranged
longitudinally along east to west, regardless of building form. However, the study
does not consider the total energy consumption including the energy consumed for
lighting.
COOL
TEMPERATE
ARID
TROPICAL
Figure 3.4: Optimum high-rise building form according to climatic zones.
Source: Yeang, K (1994)
Olgyay (1963) suggested a series of building’s width to length ratio
depending on different climatic zones. Based on the environmental criterion, the
study also established an optimum ratio factor. The hot and humid region adopted a
ratio ranged between 1:1.7 and 1:3, where 1:1.7 was considered the optimum shape
that can be applied.
Several methods have been employed to determine the height of the high rise
buildings (ASHRAE, 1997; Dowrick, 1977; Abdul Majid, 1996) that were developed
for wind flow studies. The actual height of high-rise buildings in Malaysia is
62
between 5 and 88 storeys (Abdul Majid, 1996; Loewen et.al, 1992). The average
height of typical office building in Malaysia is about 25 floors (Abdul Majid, 1996).
b)
Sectional Height
The floor to ceiling height or the floor-to-slab height also influence on the
overall building height. Yet in an environmental point of view, the height is
conducive for accessibility of daylight and natural ventilation into the floor plate.
Though it might penetrate unwanted heat inside, the floor to ceiling height is an
important factor in configuration of the building form. According to Harrison
(1998), recommended height for standard intelligent building is about 20-25 floors,
with a floor-to-ceiling height of 2.8 meters and floor-to-slab height of 3.8 meters.
3.1.3.2 High-Rise Building Core
Core is the physical mean for vertical movement within a high-rise building.
It contains with elevators, staircases, dumbwaiters, and all means of vertical access
and services in the building. Often the elevator shaft is used as a structural
component, creating an enclosed space. In a climate adaptive high-rise buildings
there are three possible core positions: central core, double core at sides and single
side core (Yeang, 1994) (figure 3.5). Thus, core can be used as thermal buffer zones
to the internal space as well as preventing heat gain through direct solar radiation.
Similar results were obtained by Larasati et al (2003), where lowest energy
consumptions (lighting and cooling) were reported for core positioned on the east
and west orientations. Further, low energy consumption was indicated for square
shape with central core option. This could be acceptable because of daylight
utilization, which reduces the electricity consumption for artificial lighting.
Therefore, from energy point of view, it is assumed that square foot print with central
core and rectangular foot print with double core on either side are preferable options
for tropical climatic condition like Malaysia.
63
Cool
Temperate
Arid
Tropical
Figure 3.5: Arrangement of vertical core according to climatic zones
Source: Yeang, K (1994)
In another study by Kannan (1991) showed that there was a direct influence
between core position and the building cooling loads (figure 3.6). According to the
study, the maximum cooling loads were reported for center core option and
minimum cooling loads were obtained for double core positioned on the east and
west orientations respectively.
Figure 3.6: Core plan and annual cooling loads.
Source: Kannan, K.S (1991)
64
3.1.3.3 The Floor Plan
The floor area is the most commercially decisive element in terms of- net
rentable area (NRA) and gross floor area (GFA) in a high-rise building. The market
values for the floor plate sizes changes according to building types such as office,
commercial, and hotel. It also depends on the city and country in which the building
is located. In other words, consideration of occupant’s quality of life, responding to
the local cultural patterns and the local climate should be the primary design
decisions.
Design interpretations are manifold in climate responsive options such as to
allow natural ventilation, penetration of daylight into the floor plate and access for
views. Response to climatic forces may determine on the size of the floor plate.
Thus, the maximum distance from periphery is a determinant factor in which case the
resultant floor plates become either small or deep in depth. There is no literature
found which determines the depth of the floor plate as an effect on the building
energy use. However, plan ratio and plan shape are directly influenced by the
building form. Therefore, in an energy and environmental aspect, the depth of the
floor plate can be determined by the width to depth ratio factor (Yeang, 1994).
Overview of existing office buildings by Harrison et al (1998) and the
ASEAN-USAID (Loewen et al,1992) revealed important details on gross internal
floor area, density of occupation per person, size of cellular office room, and depth of
the floor plate. These details were set out to determine a simplified high-rise
building configuration in South Asian region.
a)
Gross Internal Floor Area
The analysis concluded that gross area for internal floor plate range between
650m2 and 2000m2. However, according to the analysis by Harrison et al (1998)
typical internal floor area ranges between 900m2 and 1100m2.
65
b)
Cellular Office Room
The density of occupation per person varied from a gross internal area (GIA)
of 9.5m2 to 36m2 (Harrison et al, 1998). The range changes according to the
activities involved in the occupied area. The basic office depth is determined by the
perimeter depth of the correspondence office buildings. The standard dimensions for
a office room is 3 meters wide by 4.5 meters deep (based upon 1.5 meters grid)
(Harrison et al, 1998).
However, Robbins (1986) suggested some important factors to determine the
office room geometry from a daylight point of view. The study was performed based
on the ‘lumen method’ daylight analysis. The analysis showed, that maximum values
were reported for coefficient representing the proportional relationship for ceiling
height, room width and wall reflectance. This condition happened when the ceiling
height is above 2.4 meters and room width is 6 meters. This indicates a ratio of 1:2.5
between the ceiling height and room width.
In another experiment Littlefair (1999) suggested a minimum ratio for a daylit room to be 1:2:2 (ceiling height x width x depth). The findings were based on the
daylight factor recommended by the CIBSE manual for non-domestic buildings.
c)
Perimeter Depth
The findings by Harrison et al (1998) revealed that mean percentages of 59%
of office spaces were located within 0 to 6 meters perimeter-zone, 36% within 6-12
meters and only 5% had a space depth more than 12 meters. This indicates that
office work space distribution is determined by climatic responsive criterions.
Hence, office building users demand for fresh air and natural light. Based on these
findings the intelligent building (IB) study for South East Asia recommended
following options for office building planning:
66
i. Net internal area within 6 meters of external or atrium walls are suitable
for cellular office accommodation or open plan offices.
ii. Net internal area within 6-12 meters of external or atrium walls are
suitable for open plan offices and closed offices.
iii. Net internal area deeper than 12 meters is suitable for computer rooms
and presentation suits.
According to the data obtained from the ASEAN-USAID (Loewen et al,
1992) the mean average of the air-conditioned space in high-rise office buildings in
Malaysia was about 80% of the gross floor area. The core area of the building was
considered as non-conditioned area. This indicates a high amount of energy
consumption for cooling the building. Thus, these buildings were not meant to
incorporate the climatic benefits to reduce the building energy consumption.
3.1.3.4 Building Envelope
Physically high-rise buildings have a greater perimeter wall area exposed to
the external climatic conditions. The adverse environmental conditions of solar
radiation, glare, temperature, humidity, wind, noise, rain, insects, dust and smoke
makes the role of high-rise building envelope a complex one. Objectives of a
building envelope remains on its contribution to the reduction in energy
consumption, protecting from direct solar radiation penetrating to the interior, glare
reduction, minimization of water penetration, providing natural ventilation, reduction
of external reflection, providing view and to act as a thermal barrier. Depending on
the climatic zones and particular site conditions, the intensity of the environmental
force changes.
The design parameters related to the envelope that determine its thermal
response to the climatic conditions include: thermo-physical properties of the
building material, window-to-wall ratio, location of the windows and sizes, glazing
67
properties, shading of window and envelope, insulation system and the surface
treatment of the enclosing envelope (Kannan, 1991).
a)
Window
In an energy point of view, different climates indicated different values of
window-to-wall ratio (WWR) to optimize the energy savings. According to the LT
method (Baker & Steemer, 2000), the optimum energy can be achieved between 20%
and 40% of WWR depending on the orientation. The daylight illuminance suggested
by the above study at work stations was estimated as 500lux.
Hamdan (1996) reported that window for light and ventilation according to
‘The Malaysian Uniform Building By-laws’, for commercial buildings requirement
as 10% of the floor area. However, an experiment carried out by Azni Zain-Ahmad
et al. (2002) suggested that the optimum window opening for adequate daylight and
minimum solar heat gains in an office space is about 25% from the wall area.
However, this experiment was carried out for room depth of 2.75meters. The
average window size of the office buildings in Malaysia is about 50-60% of the wall
area (Kannan, 1991). The high WWR may be due to development in glazing
products or extensive use of glazing as an architectural design style or for maximum
daylight utilization is yet to be decided. Huang (1992) revealed that the optimum
lighting energy savings can be achieved with daylight aperture ratio (glazing light
transmittance x window-to-wall ratio) between 1.5 and 2.0 for a 500lux internal
target illuminance, under clear sky conditions.
b)
Building Envelope Treatment
Reviews on shading strategies and building envelopes on existing buildings
in Malaysia were conducted by several authors; Stewart (1977), Hassan, KAKU
(1996) and Abdul Majid (1996). According to Abdul Majid (1996) building
envelope treatments in high-rise office buildings in Malaysia can be classified into
five major categories: external solar shading devices, perforated screens, articulated
68
facades, dual skin envelopes and glass curtain walls. Hassan KAKU (1996) reported
that although shading strategies are prime criteria in reducing the impact of solar
radiation, in most cases the selected devices do not meet the minimum shading
requirement. Review on solar shading strategies, design variables and the
effectiveness of shading strategy are discussed in section 3.3.
3.1.3.5 Court Yards, Atria, Wind Scoops and Open Corridors
Court yards, atria, wind scoops and open corridors are required for deep plan
office buildings for the provision of natural ventilation and daylight. Large multi
storey transitional spaces can be introduced in the central and peripheral parts of the
buildings (Yeang, 1994). Introduction of these elements reduces the plan depth of
floor plate while increasing the surface area. This enables to take benefit of natural
ventilation and daylight, which will eventually affect the total building energy
consumption.
Abdul Majid (1996) states, according to the Malaysian Uniform Building ByLaws (1984), the required minimum size of an air well for a 2 to 7 storey building is
7m2 and for buildings more than 8 storey high is 15m2. The width of such air-well is
about 2.5 meters. Although these articulated spaces were extensively used in modern
high-rise buildings, there is no literature found on configuration of such spaces
related with the height of the building or other design variables.
From the above analysis, it is clear that configuration of a high-rise office
building involves large number of inter-related design parameters. Therefore it is
difficult to simplify the high-rise office building into a single configuration, in order
to represent the climatically interactive high-rise buildings in hot and humid climatic
regions. However, the above analysis is used to determine the characteristics of the
base model for a ‘typical office room’ to investigate the influence of external shading
strategies on solar heat gain, daylight distribution and energy consumption.
69
The review on office buildings indicated that energy consumption for cooling
and lighting are high in Malaysian and other South East Asian countries. Therefore,
it is important to understand the variables affecting the cooling load and lighting
energy consumptions. Thus, the basic principles of heat gains and types of heat
transfers are discussed in following section.
3.2 Heat Gains
Space heat gain is the rate which instantaneous heat enters into or generated
within the space at a given instance. Heat gain is classified by the mode in which it
enters the space. The unit of heat is the ‘Joule’ (J) and unit of heat flow rate is the
‘watt’ (w).
3.2.1 Modes of Heat Transfer in Buildings
Heat flows from one body to another or from one surface to the other when
ever there is temperature difference. In other words, heat transfer from a higher
temperature towards a lower temperature occurs with respond to temperature
gradient. Hence, heat can be transported, yet neither heat nor energy can be created
or destroyed, which characterizes the principal of conservation of energy. Heat
transfer occurs in three modes, conduction, convection and radiation.
3.2.1.1 Conduction
In conduction, heat is transferred within a substance or between substances
that are in direct physical contact. All materials vary according to their ability to
conduct heat (Kannan, 1991). Thermal conduction in buildings is thus the process of
heat transfer through solid materials such as walls and roofs from the hotter side to
cooler side of the building elements. The thermal conductivity of the material and
70
the thickness of the element determine the effectiveness of the conductive heat flow
rate of the correspondence element (Givoni, 1998).
3.2.1.2 Convection
Convection heat is transported within the substances it self. The driving force
of the process is associated with the flow of matter, for example motion of the fluids
or from the temperature differences. The rate of convection heat transfer depends
mainly on the air speed next to the correspondence building surface.
3.2.1.3 Radiation
Radiation consists of electromagnetic wave traveling at the speed of light.
But unlike conduction and convection, radiation requires no medium for its
propagation (Kannan, 1991). It is stated in the field of thermodynamics that all
matters continuously emit and absorb electromagnetic radiation unless its
temperature is absolute zero (Eastop & McConkey; 1993). In response to
temperature gradient, if an object absorbs more than it emits, then the temperature
rises and vice versa. An equilibrium state occurs when absorption and emission of
radiation are equal and when the object temperature is constant. According to the
wavelength, two distinct radiant energy types occur; long wave radiation and short
wave radiation. Intensity of short wave solar radiations is higher than the long wave
thermal radiation, which is emitted by surfaces with higher temperature than
surrounding temperature. Surface properties; emisivity, absorptivity and reflectivity
are determining factors of long wave radiation (Givoni, 1998).
In practice heat may be transferred in combination of the above stated modes.
But the phenomenal characteristics of each mode enable to determine the effect of
each mode separately. Radiation is the principal means, where the earth and
71
atmosphere gains heat from the sun. Radiation is also the principal means of heat
escape from the surface to space.
The thermal performances of buildings depend on the amount of heat gain
from two kinds of parameters: through building design variables and internal heat
gains. Effects of these variables on the thermal performance will not be the same.
Some may have more influence than the other on the thermal response due to their
physical characteristics and mode of heat transmission. In that sense, solar heat gain
through the window has a significant impact on the building thermal performance
than other building design variables. In order to compute these heat gains through
the windows, thermal properties and configuration of heat transmission through the
window need to be understood.
3.2.2 Types of Heat Transfer in Buildings
Buildings are subjected to periodic variations of temperature and heat gains.
Thus depending on the heat sources, heat gains can be categorized into two types:
heat gain through building design variables and heat gain through internal sources.
Heat gain through building design variables includes: conduction heat gain, solar
radiation through fenestrations, sky lights and infiltration. The internal sources of
heat gains are from: artificial lights, occupants and equipments.
3.2.2.1 Heat Transfer through Building Fabric
Heat gain occurs through solid surfaces, such as exterior walls and roofs,
interior walls, exterior windows, interior windows and surfaces in-contact with the
ground. For surfaces in contact with outside air, conduction is determined by out
side conditions (air temperature, ground surface temperature, wind speed, wind
direction and the solar radiation intensity), inside conditions (room air temperature),
orientation and the material properties of the wall and window (surface conductance,
72
surface resistance, thermal transmittance). Heat gain through surface contact with
ground is determined by ground temperature, room air-temperature and the material
properties of the wall or floor (Givoni, 1998).
Conduction heat flow rate through the building fabric can be described by the
equation:
Qc = UA (∆T)
(3.1)
Qc; Conduction heat flow rate, W
U; Transmittance value, W/m2K
A; Surface area, m2
∆T;
Temperature difference, 0C
3.2.2.2 Heat Gain through Window
Heat gain through the window occurs via two methods; direct solar radiation
transmission through the glazed area and absorbed radiation transmission into the
space. Heat gain through the fenestration has high influence on building cooling
load (Lam and Li, 1999). The amount of solar gain through the window depends on
several factors; the intensity of solar radiation on the window and the incident angle,
the transmittance and conductance of window glazing and the associated mounting
frames, and the thickness of the glass pane (Bülow-Hübe, 2002).
The impinging solar radiation on a window glass is divided into three
fractions; radiation that is reflected outward, radiation that is absorbed within the
glass and radiation that is transmitted through the window system (figure 3.7). Other
than the reflected fraction to the outward of the building, absorbed and transmitted
fraction of the radiation effect on the building temperature which need to be
eliminated actively. The optical properties of concern for a glazing type are
reflectance (ρ), absorptance (α) and transmittance (τ), which correspond to the
73
reflected, absorbed and transmitted solar radiation respectively. The sum of the
reflectance, absorptance and transmittance of a glazing layer thus stated as
(ASHRAE 1993):
ρ+α+τ=1
(3.2)
Heat exchange through the window occurs via three physical effects:
i. Conductive and convective heat transfer: given as U-value or overall
coefficient of heat transfer.
ii. Short wave solar radiation incident on the window: direct from the sun, after
scattering from the atmosphere and after reflection from ground or adjacent
objects.
iii. Long wave solar radiation which is absorbed and reradiate to the atmosphere.
This can be expressed by (ASHRAE, 1993):
Total heat
admission
through
glazing
=
Heat flow due
to outdoorindoor
temperature
difference
+
Total Incident Solar
Radiation
Radiation
transmitted
through
glazing
+
Inward flow
of
(3.3)
absorbed
solar radiation
Absorption (α)
Transmittance (τ)
Glazing
Reflection (ρ)
Figure 3.7:
Instantaneous heat balances through sunlit glazing material
74
a)
Thermal Transmittance
The thermal performance of a window device is described by the U-value.
This is the heat flux through the window per unit surface area (A) and degree
temperature difference between the out side (to) and the inside (ti) of the window,
(W/m2K or Btu/Hr.ft2-F) (Koenigsberger et al. 1975).
Qwin = UA (to – ti)
(W/m2K)
(3.4)
The total U-value is usually applied to the whole window, including sash and
frame. But in general, center-of-glass U-value is stated and recommended to state
the total U-value of the window (Bülow-Hübe, 2001).
Uwin = Uglass . Aglass + Uframe . Aframe + Uedge . Aedge
(W/m2K) (3.5)
Aglass + Aframe + Aedge
Where Uglass, Uframe, and Uedge are the U-values of the respective zones, Aedge,
Aglass, and Aframe are the respective areas. In another method, a linear heat
transmittance coefficient ψedge (W/mK) is being used to calculate the edge effects.
The total window U-value then becomes (Bülow-Hübe, 2001):
Uwin = Uglass .Aglass + Uframe .Aframe + ψedge .L edge (W/m2K)
(3.6)
Aglass + Aframe
Where Ledge is the length of the edge between the frame and the glass. In this
case the total thermal performance depends on the different parts of the window.
The main difference between the basic principles of heat transfer through
thermal conductance and thermal transmittance is important. In thermal conductance
75
the heat flow rate is considered from one surface to the other surface, while thermal
transmittance occurs from air on one side to the air on other side through the building
section (walls, window, roof, floor etc). Therefore thermal transmittance or U-value
of a window system (including frame, sash, shading devices) depend on the
following factors; number of air spaces between glazing and the type of gas, size of
the window, properties and treatment of the glazing material, and the materials and
detail of window frame (Givoni, 1998; Bülow-Hübe, 2001).
The heat transfer through glazing with air gaps occurs basically through long
wave radiation exchange and convection in the air gaps of the glazing (Bülow-Hübe,
2001). The air gaps add to the thermal resistance of the glazing, thus reducing its
overall heat transfer coefficient (U-value). Therefore the thermal resistance of the
glazing (Rtot) can be expressed as the sum of the resistances of different gaps (Rgap),
individual glass pane (Rgl), internal (Rsi) and external (Rse) surface resistances.
Rtot = ΣRgap + ΣRgl + Rsi + Rse
(m2K/W)
(3.7)
The U-value is the inverse of the total thermal resistance (Bülow-Hübe,
2001):
Ucenter of glass = 1/ Rtot
(W/m2K)
(3.8)
Increase of thermal resistance of layers gives a lower U-value. Thus, the
lower U-value, create better insulation.
b)
Radiation Transmittance
The solar radiation transmitted through a window pane consists of two parts.
The direct transmittance of solar energy or the primary solar transmittance (τ) and
secondary heat transfer process. The secondary internal heat transfer factor is the
absorbed heat (α) transported inwards to the room. The total solar energy
transmittance specifies the total fraction of incidence solar energy that is transmitted
76
through a building component. The common term used to define the solar energy
transmittance in building components is the ‘solar heat gain factor’ (SHGF). The
hourly solar heat gain factor for the horizontal surface is derived using the ASHRAE
(1997) clear sky model, which is given by:
SHGFh = Ibh (τb + Ni αb) + Idiff,h (τdiff + Ni αdiff )
(3.9)
Ibh : Hourly direct beam radiation on horizontal glazing (W/m2)
Idiff,h : Hourly horizontal diffuse radiation (W/m2)
τb & τdiff: Transmittance of reference glazing for direct beam and diffuse
radiation
αb & αdiff: Absorptance of reference glazing for direct beam and diffuse
radiation
Ni : Inward flowing fraction of the absorbed radiation
Ibh and Idiff,h can be calculated using corresponding measured hourly
horizontal global radiation, IGh.
For the vertical surface, hourly SHGFv (W/m2) is expressed as:
SHGFv = Ibv (τb + Ni αb) + Idiff,v (τdiff + Ni αdiff )
(3.10)
Where,
Idiff,v : the sum of hourly diffuse and reflected radiation on the plane of
vertical glazing, (W/m2).
Ibv : direct beam radiation on vertical plane, (W/m2)
The vertical components, Ibv & Idiff,v can be determined as follows:
Ibv = (Ibh / sinβ)∗ cosθ
(3.11)
77
Idiff,v = IGv - Ibv
(3.12)
Where,
β: solar altitude (degree)
θ: angle of incidence (degree)
IGv: hourly global solar radiation on vertical plane (W/m2)
The transmittance and absorptance for direct radiation are a function of the
incident angle of the solar beam relative to the surface. Fifth order polynomials to
express these properties in terms of angle of incidence have been used.
τ = C1 + C2Cos (θ) + C3Cos2 (θ) + C4Cos3 (θ) + C5Cos4 (θ) + C6Cos5 (θ)
(3.13)
And
α = A1 + A2Cos (θ) + A3Cos2 (θ) + A4Cos3 (θ) + A5Cos4 (θ) + A6Cos5 (θ)
(3.14)
For diffuse radiation, Stephenson (1965) calculated τdiff and αdiff to be 0.799
and 0.0544 respectively. Values of the constants C1, C2, C3, C4, C5 & C6 and A1,
A2, A3, A4, A5 & A6 depends on the glass type and the number of panes. Referred
values were obtained from the DOE-2 Engineering manual (1982).
The inward flowing fraction Ni of the absorbed radiation can be expressed as:
Ni = hi / (hi + ho)
(3.15)
Where hi and ho are the heat transfer coefficients of the inside and out side
glazing surfaces respectively, given in W/m2 K. Inward flowing fraction for single
glazing is 0.268, reference to the ASHRAE fundamentals (1993). This value is used
for the present calculations.
78
Hence, the secondary heat transmission from the absorbed solar radiation can
be given as:
τa = Ni α = 0.268 * α
(3.16)
The total heat gain (THG) through window is given as (Kannan, 1991):
T.H.G (Qs,win) = SHGFv + UA (to – ti)
(W/m2)
(3.17)
For a particular window, solar heat gain is proportional to the amount of solar
radiation incident on its exposed window pane. The geographical variations in solar
radiation availability depend on two factors (Li and Lam, 2001).
i. The latitude related variations due to changes in the solar position in the sky
ii. Climate related variations, such as factors affecting the sky condition, e.g. air
mass, cloud cover, atmospheric turbidity etc.
These two factors are essential variables for the SHGF analysis. Therefore it
is important to determine the appropriate SHGF for that particular location of the
building study.
3.2.2.3 Infiltration
Infiltration is due to outside air entering the space through the wall cracks and
gaps between external windows and doors. The heat gains through infiltration
depend on wind speed, opening area and out side temperature difference (ASHRAE,
1993). Opening of internal or external window or door for various reasons also
affect the infiltration of heat gains or losses. The sensible heat component depends
on the outside-inside air temperature difference and the latent heat component
depends on the outside and inside humidity ratio difference.
79
Heat gain due to infiltration is calculated as (ASHRAE, 1993)
Qv (sensible) = 1.23Q (to – ti)
(3.18)
Qv (latent) = 3010Q (Wo – Wi)
(3.19)
Qv (total) = 1.20Q (Ho – Hi)
(3.20)
Q: ventilation air flow (L/s)
to, ti: outside, inside air temperature, oC
Wo, Wi: outside, inside humidity ratio, kg (water)/ kg (dry air)
Ho, Hi: outside, inside air enthalpy, (kJ/kg)(dry air)
3.2.2.4 Impact of Electric Lighting
The heat gain from electric lighting depends on the intensity of lighting in the
space, type of lighting (incandescent, fluorescent, etc.) and the lighting schedule.
However, when daylight is incorporated with artificial lighting system, the lighting
heat gain depends on the availability of daylight in the space.
According to Lam and Li (1999) the electric lighting is often the largest
cooling load component, especially in the core (towards interior from the perimeter
space) of the building. Effectiveness of the heat gain on the cooling load depends on
several factors; the amount of light energy emitted into a room, the internal mass and
furniture and the room temperature. Robbins (1986) explains that lighting energy
emitted into a room as radiation is affected on the cooling load after it has been
absorbed by the interior mass of the building and re-radiate as heat energy.
Therefore, the rate of heat gained to a room’s air from the lighting system can be
different from the rate to the power supplied to the system. The instantaneous rate of
heat gain from electric lighting can be calculated from (ASHRAE, 1993):
Qel = 3.41. W. Fu.. Fs
(3.21)
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Qel (Watt): Heat gain from electric lighting
W: total light wattage
Fu: Light use factor
Fs: Lighting special allowance factor
The cooling load is equal to the lighting load multiplied by a cooling load
factor or by a weighting factor depending on the cooling load calculation method.
A simplified method to determine the impact of daylight on cooling load
when integrated with the artificial lighting system was introduced by Robbins
(1986). The method implies the electricity energy use on space cooling due to
daylight utilization can be determined by function of differential cooling energy use
in identical daylight and non-daylight rooms or buildings. The total energy use for
cooling can be expressed (in W/m2) as a function of average unit power density in
the following quadratic equation (Robbins, 1986):
Qcl = 7.29 + (0.34 UPD) + (0.005 UPD2)
(3.22)
Qcl: cooling energy use
UPD: average lighting unit power density for the room or building (W/m2)
The differential energy use (DEU) for cooling with daylight and non-daylight
room (or building) would be:
∆DEU CL = EUcl, daylight - EUcl, non-daylight
(3.23)
If ∆ DEU CL is a positive value, an increase in cooling energy use occurs
because of the use of daylight as an interior illuminant. Vis-à-vis a negative value
indicates decrease in total cooling energy use. The energy analysis of daylight and
non-daylight building can be very useful in calculating the energy saving potentials
and establishing a well balanced daylight system.
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3.2.2.5 Occupants Heat Gains
Occupants produce both sensible and latent heat gains. The occupancy
pattern is defined by the density of users and the character of the activities they carry
out in a given building. Generally there are four basic types of occupancy patterns
identified (Chavez, 1989): variable occupation (e.g. Design offices), full occupation
(e.g. Clerical offices), intermittent scheduled occupation (e.g. in schools classroom)
and intermittent occupation (e.g. Store rooms & warehouse spaces). It is reasonable
to expect especially in office spaces that these occupancy types (variable and full
occupation type) overlap at times. The internal heat gain from occupants is
determined from (ASHRAE, 1993):
Qi (sensible) = No x Sensible heat gain (W)
(3.24)
Qi (latent) = No x Latent heat gain (W)
(3.25)
No is number of people in space
3.2.2.6 Equipment Heat Gains
Equipment heat gains are produced by the electrical equipments such as
computers, photo copy machines, hot water heaters and other machineries. These
equipments can produce both sensible and latent heat components which depend on
the kW power of the equipment and on the schedule they have been using. The
internal heat gain from appliances is determined from (ASHRAE, 1993):
Qeq (sensible) = (qis . Fua . Fra) / Ffl (w)
(3.26)
Qeq (latent) = (qil . Fua)
(3.27)
(w)
qis: sensible heat gain from appliances
qil: latent heat gain from appliances
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Fua: use factor
Fra: radiation factor
Ffl: flue loss factor
Predicting the thermal performance of a building involves the handling of a
large number of interrelated parameters. Not all the variables affect the thermal
performance of the building in the same way. Some may have more influence over
the building thermal response than others. However, it should be recognized that it is
impossible to optimize all criteria simultaneously. In this study it argues that heat
entering through the fenestration has a significant impact on the building thermal
performance than other variables. Also, the fenestration has direct influence on
daylight level in the building, which also again influences the use of artificial
lighting at inadequate daylight illuminances. Thus, it can be argued that heat gain
through fenestration, daylight level and heat gain from artificial lighting are
interrelated, while others are independent from fenestration design. In other words,
fenestration may affect on building energy use by means of thermal heat transfer,
solar heat gains, air leakages and daylight. Hence, it can be argued that the role of
solar shading required a re-thinking in terms of balancing the positive and negative
influences of the climate.
3.3 Solar Shading
The solar radiation received by the earth is categorized into three main
divisions; direct, diffuse and reflected radiation. The solar energy that enters the
building through external wall apertures can cause serious performance problems
such as over heating and high air-conditioning cost, increase internal air temperature
which affect on occupants thermal comforts, cause glare and create visual
discomforts.
With this back ground to the problem, the basic principle of the sun control or
shading is to regulate heat by intercepting radiant heat wave penetrating into the
83
internal space (Olgyay, 1957). The solar shading devices favoured the solution to
solve the overheating problem than reducing the glazing area, which may reduce the
amount of natural lighting into the building (Chauvel et al, 1982). Further, the use of
solar shading became more attractive to architects than reducing the window area,
which may provide an alternative to the design character of the building.
Shading devices also have the advantage of improving the light distribution
into the interior. To increase the use of daylight, light shelf shading systems have
been developed which are capable of redirecting direct or diffuse light into the
interior (Chavez, 1989; McHugh, 1995; Abdullah-Abdulmohsen, 1995; Dubois,
2001). However, total prevention of solar radiation may decrease the daylight
penetration into the deep end of the room, thus increasing the use of artificial lighting
to illuminate the interior.
The use of solar shading is one of the solutions to solve the glare problems in
modern office buildings. The variable of consequence in glare discomfort appears to
be the luminance of the sky as seen through the window. Thus, limiting the daylight
glare index is best achieved by limiting the luminance or the visibility of the sky seen
through the window by means of external or internal solar shading devices (Chauvel
et.al, 1982; Abdullah-Abdulmohsen, 1995).
External projections on windows also tend to create strong pressure gradients
between openings in a room. This results in providing good ventilation conditions
and increase in air flow through the correspondence room (Givoni, 1998; Malsiah,
2001).
Further, experiments have indicated solar shading as an influential element in
manipulating the energy consumption in buildings. Impact of solar shading on
cooling loads, heating loads and daylight contribute directly to the building energy
consumption (Bojic et al, 2002; Bulow-Hube, 2001; Dubois, 1998; Lee et al, 1998;
Abdullah-Abdulmohsen, 1995; Busch, 1992; Harkness, 1988). Thereby solar
shading has become a design alternative for architects not only as an aesthetic
84
element or to protect from adverse environmental conditions (sun, wind, rain and
glare) but also to regulate energy consumption in buildings.
Although the primary function of the solar shading device is to block direct
sun, the solar heat gain and energy utilization is large with shading devices. Shading
devices also have the risk of reducing the potential for daylight which in turn
increases the use of artificial lighting. Therefore it can be argued that the solar
shading design strategies required to be rethinking in light of energy efficiency.
3.3.1 Analysis of Types of Shading Devices
Climate conscious design in the tropics must be attempted in order to prevent
solar heat gain into the building. The primary design strategy implies that
exploration of the shading potentials is to reduce the total heat gain through the wall
openings. These strategies in broad term can be achieved by two means; natural
devices and sun control devices.
The natural shading strategies are the means of shading the building with
orientation of the sun and by the use of vegetation. Apart from the natural devices,
sun control devices are used to exclude the unwanted solar radiation penetration into
the building. The design, fixing location, effectiveness in terminating the direct sun
and operational systems are attributes of the sun control devices. They can broadly
divided into two; internal and external devices
3.3.1.1 Orientation
The orientation has a great relationship from the aspect of self shading of a
building façade from the incident solar radiation. According to the sun path, proper
orientation is the primary aspect in reducing the solar heat gain. In the region of
equatorial tropics (between 00-120 latitudes north), the most preferred orientation for
85
self shading is between 00-800 from the north (Emmanuel, 1993). Further, the above
study suggested for 00-40 latitudes, the preferred orientation for self shading is
between 3500-3600 from the north. The three dimensional form of the building can
be used to perform a self shading on its façade or adjacent facades if proper
orientation is considered in the building design.
The energy calculations in commercial buildings often neglect the impact of
the urban setting and the effect of nearby buildings (Lam, 2000). A study by the
same author on the shading effects due to nearby buildings in Hong Kong revealed a
1.2% increase in annual building energy budget. Emmanuel (1993) explored the
design strategies of urban masses for potential shading in an urban setting, thus
creating a “shadow umbrella” to enhance the comfort potentials in urban outdoors.
The main determining factors were the orientation of the location and the solar
altitude. The study identified set of generic patterns of building massing by the
shadow umbrella concept developed for latitude between 50 and 90 north.
3.3.1.2 Vegetation
The landscape and plants around buildings offer the possibility of reducing
the undesirable effect of high solar radiation. According to Papadakis et.al (2001)
the application of plants to shading buildings proved to be an efficient passive
method of solar control. The radiative and thermal loads in the shaded area proved
to be significantly lower relative to the un-shaded area. Further, the same study
revealed the evaporative cooling effect of the plants resulted in lower air temperature
around the shaded wall. Depending on the density of the vegetation, trees reduced
solar radiation transmittance from 60% to 20% compared to solar radiation
transmitted through a normal glazing without shade (Brown et.al, 2001).
However, locating and selecting the plant type should consider the orientation
of the building and the effect on daylight. Apart from the energy saving, plants also
add to the aesthetic and affect the ventilation pattern of the building (Boutet, 1987).
86
3.3.1.3 Internal Devices
Internal devices to control solar radiation can be categorized into two types;
firstly, solar shading using blinds, louvers, drapers and screens which are other than
the window glazing pane. Secondly, the use of special glazing without the use of
external or internal shading devices. Compared to external devices, the internal solar
shading devices are less effective, as they allow solar radiation to strike on the
vertical surface of the building. They also permit the heat into the building.
a)
Solar shading by louvers, blinds and drapes
Louvers can be fixed externally or internally of the window. Venetian blinds
and drapes are fixed internally only. Louvers and blinds can be adjusted to exclude
direct sunlight and to control daylight and glare. Effectiveness of these shading
systems depend on the geometry of the slat, spacing between slats, the shadow lineangle and thermal and optical properties of the slat material. Surface colours also
play a significant role in reflecting the incoming solar radiation and daylight. Detail
experiments on louvers, blinds and impact on energy were carried out by Lee et.al.
(1998) and Al-Shareef et.al (2001).
Dubois (2001) discussed about internal shading devices and their impact on
daylight quality. Klems et.al (1997) studied the performance of fenestration with
venetian blind for different slat angles and solar heat gain. The findings revealed,
solar heat gain factor for fenestrations incorporating venetian blinds depend strongly
on the incident direction of beam solar radiation.
b)
Glazing
The window glazing material has been extensively experimented and
modified in order to regulate external climatic effects of solar radiation, solar heat
transfer and daylight transmittance (Roos, A. 1998; Karlsson, J et.al, 2000; BulowHube, 2001). Different types of glazing are manufactured according to the specific
87
treatment degree on the optical properties (reflectance, absorptance and
transmittance). Solar control in glass was achieved by adding a metal oxide to the
glass, which has a tinted surface that re-radiates the heat to the out side. However
this kind of tinted glazing reduces daylight penetration. Combination of solar control
properties with energy efficiency in glazing enables to let large part of daylight and
intercept unwanted heat gains into the building. Such glazing is manufactured based
on special type of spectral selective coatings. Most common types of glazing are;
clear glass, heat absorbing glass, heat reflecting glass, low-emissivity glass, super
insulating glass, grey and coloured glass (Givoni, 1998).
Glazing should be selected based on the external climate conditions and
expected building’s internal environment. For heat dominated buildings in cold
climate, the glazing should have a high transmittance which admits most solar
radiation heat and a high reflectivity in the long wave part of the spectrum. This
implies, having a low emittance (Low-e) in the same wave-length region suppresses
the radiation out wards, resulting in long-wave radiation being reflected back into the
interior (Bulow-Hube, 2001). This results in the “greenhouse” effect. In cooling
dominated building, glazing should eliminate all UV (ultra-violet) and IR (infrared)
radiation transmittance out side the visible spectrum. In other words, the total solar
heat gain is reduced without significant loss of light transmission.
Many research works has been carried out to understand the effect of
different glazing types on energy consumption. Further, researches were carried out
to establish a system for energy labeling, energy rating of windows compared to a
standard window (Sekhar et.al, 1998; Karlsson, J et.al, 2000; Citherlet S. et.al, 2000;
Bulow-Hube, 2001; Bodart et.al 2002; Bojic et.al 2002).
External glazing types such as heat absorbing, heat reflecting and low-e are
used to reduce solar heat gains into the building. Yet, the trapped solar heat inside
the building due to re-radiation may affect on overall energy consumption. Further,
controlling the high glare problem in hot and humid climates is less favorable with
glazing types. Also, the impact of innovative glazing types on overall energy use
88
need to be experimented under tropical climate conditions before they were applied
in buildings.
3.3.1.4 External Devices
External devices are projections attached to the building skin or an extension
of the skin to eliminate unwanted solar heat. They are more effective as they
intercept the solar radiation before it reaches the vertical surface of the building
envelope. The obstructed heat is dissipated to the out side air. Thus, heat reduction
is best achieved by excluding unwanted heat rather than removing it later.
The horizontal (overhang) and vertical (fins) devices are the two basic forms
of external shading devices. The egg crate devices are combinations of the
horizontal and vertical devices (figure 3.8). Based on these basic forms,
configuration of the external shading devices varies from structural projections in the
form of cantilevered floor, recessed walls and shading devices using light weight
materials. The form of horizontal and vertical fins and light shelves perform a
similar function. Use of lightweight materials enabled to give more flexibility in
operating solar shading. Configurations of operable shading device were able to
change or adjusted to the changing patterns of sun’s motion and the shading needs.
Therefore, the performance of an operable device in eliminating the unwanted heat is
better than a fixed device (Givoni, 1998). The fixed device needs no handling by the
occupant and free of maintenance, while operable devices need frequent maintenance
to keep them in good condition. Operable system is more useful in temperate and
cold climates as it can be adjusted to get more favored solar heat during winter but
obstruct the heat gains during summer. In the tropics, it can be useful to control
glare, daylight and solar heat gains. Advent of technology has enabled development
of automatically controlled operable devices with solar sensors for efficient use.
Canopy and awnings are another form of external horizontal solar shading
device, mostly used for high solar altitudes. Effectiveness of the canopy and the
89
awning depends on; material used (thermal and optical transmittance, colour),
geometry and fixing position and details (Dubois, 1999). Studies done by the same
author indicated that the canopy or awning angles (to vertical surface) are also an
important aspect in reducing building energy consumptions.
However, there are structural and architectural limits in designing external
projections (Kannan, 1991). Excessively long projections can be alternated with
number of smaller projections at different heights and widths to obtain the same solar
protection (Olgyay, 1957). In most cases, limitations were imposed based on
structural and architectural reasons, than concerning on the energy implication.
Daylight distribution, solar heat gain, solar heat loses and ventilation distribution can
be regulated by the solar shading devices. Separate studies are being carried out to
understand the implication of solar shading on each parameter. However, little is
known about the relationship between energy use and shading device geometry,
especially under tropical climate conditions.
Horizontal
Vertical
Egg-crate
Figure 3.8: External solar shading devices, horizontal overhang, vertical shading
devices and egg-crate devices.
Source: Olgyay, V and Olgyay, A (1957)
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3.3.2 Method of Designing a Shading Device
3.3.2.1 Shadow Angles
Determining external shading device geometry depend on two shadow
angles; horizontal shadow angle (HSA) and vertical shadow angle (VSA). Shadow
angles express the sun’s position in relation to the building façade of given
orientation which describes the shading mask produces by a given device. Also
specifies a device required to shade from the direct solar radiation at that particular
time and orientation.
Horizontal shadow angle (HSA) is the difference in azimuth between the
sun’s position and the orientation of the building façade considered, when the edge
of the shadow falls on the point considered (figure 3.9). The horizontal shadow
angle describes the performance of a vertical shading device.
Figure 3.9:
Horizontal shadow angle (HSA)
HSA = AZIMUTH-ORI (façade orientation)
(3.28)
(+HSA when sun is clockwise, Azimuth > Orientation; -HSA when sun is anti
clockwise, Azimuth < Orientation)
Similarly, the vertical shadow angle (VSA) is measured on a plane
perpendicular to the building façade. Thus vertical shadow angle can be considered
as the angle between a line perpendicular to the wall and the projection of the tilted
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plane which contains the sun or the edge of the shading device (figure 3.10). The
existence of the VSA depends on the HAS when the latter is between -900 and +900.
In other words when the sun is behind the considered façade (VSA > 900), the façade
itself is self shaded. The VSA determines the horizontal shading projection
geometry.
VSA = ATAN {Tan (ALT) / Cos (HSA)}
Figure 3.10:
(3.29)
Vertical shadow angle (VSA)
3.3.2.2 Shading Mask and Sun-Path Diagram
The sun-path diagram is a two dimensional graphical presentation of the three
dimensional sky vault. The relationship of solar time, day of year, solar azimuth
angle, solar altitude angle, are present in sun-path diagram for correspondence
latitude. According to the projection method of the sky hemisphere, different sunpath diagrams were developed. The equidistant projection, orthographic projection,
and stereographic projections are the most widely used methods (Olgyay, 1957;
Mazria, 1979; Szokolay, 1996; OH, K.W 2000).
The shadow angle protractor represents the cut-off line due to the horizontal
shadow angle and for vertical shadow angle. The radial lines indicate the horizontal
shadow angle (HSA) and arc lines indicate the vertical shadow angle (VSA)
respectively (figure 3.11). When the shadow angle protractor is superimposed on the
92
sun-path diagram, the required shadow mask of respective shading device (horizontal
projection or vertical fins or egg-crate) can be traced. Thus, according to the
orientation of the façade considered, this will indicate the dates and hours under
shade when the shading is effective.
Horizontal shadow
angle
Figure 3.11:
Vertical shadow
angle
The shadow angle protractor
Figure 3.12: Stereographic projections for Kuala Lumpur
(Latitude 3.120, Longitude +101.60, and Time zone 7)
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The depth of a horizontal shading device depends on the window height and
the shading angle requirement (VSA). The shadow angle is determined by the
latitude and the orientation (figure 3.13).
D
h2
Incident solar
radiation
Hfen
h1
VSA
Figure 3.13: Relationship between horizontal shading depth, window height and
vertical shadow angle (VSA)
Depth of shading device (D) = net opening height (Hfen)
(3.30)
Tan (VSA)
Hfen = h1 + h2
(3.31)
The length of a horizontal device is defined according to the correspondence
horizontal shadow angle (HSA) as follows (Szokolay, 1996; Harkness and Mehta,
1978):
e = D*Tan (HSA)
(3.32)
Where ‘e’ is the projection side ways from the window vertical edge. If the
length of the shading device over the window is e1, then the total length (L) of the
device will be (figure 3.14):
L = 2e + e1
(3.33)
94
L
e1
e
e
Horizontal
overhang
Glazing
Wfen
Figure 3.14:
Sideway extension of external horizontal shading device
The depth of the vertical fin (f) depends on the window width (Wfen) and the
horizontal shadow angle (figure 3.15).
Depth of fin (f) = net opening width (Wfen)
(3.34)
Tan (HSA)
Incident solar radiation
f
HSA2
HSA1
Vertical fins
Glazing
Wfen
Window in Plan
Figure 3.15: Relationship between vertical fin’s depth, window width and
horizontal shadow angle (HSA)
3.3.2.3 Awning Geometry
The geometry of awnings and angular horizontal shading devices depends on
the angle of the device to the vertical plane, which cannot be determine using
shading mask and sun path diagram. The length (L) and the width (Wawn) of the
angular shading device were determined according to solar altitude and azimuth
95
angle of the correspondence location of the shading device. Hence, the length (L)
and width (Wawn) were determined using the following equations (Dubois, 1999):
L=
Hfen. Cos (VSA)
.
(3.35)
[(Tanϕ. Tan β ) + Cos (VSA)] Cosϕ
Wawn = 2 [L. Sinϕ. Tan (VSA)] + Wfen
Wawn
é
Wfen
é
(3.36)
Awning
h =Lsinϕ
v
L
Fh
ϕ
L
(Fh -v)
Fh
d
Shado
β
VSA
Window
ELEVATION
Figure 3.16:
SECTION
Awning geometry. Source: Dubois, Marie- Claude (1999)
Equation (3.35) and (3.36) were derived from the following;
L = v/ Cos (ϕ)
(3.37)
v = Hfen - d Tan (β )
(3.38)
d = h/ Cos (VSA)
(3.39)
h = L Sin (ϕ)
(3.40)
é = L Sin (ϕ).Tan (VSA)
(3.41)
96
L: awning length (m)
v: vertical projection of the awning (m)
h: horizontal projection of the awning (m)
ϕ: awning, slope (0)
d: horizontal projection of the distance between the awning’s lower corner
and its shadow on the vertical wall (m)
0
β: lowest solar altitude for the period considered ( )
é: awning width exceeding the window width on each side (m)
The design of the external shading devices depend on the changing sun path
at different times of the year, for given latitude and the orientation considered.
Therefore, the geometry of the shading device also needs to change depending on the
required shading area. When determining a full shading of the window we need to
establish three basic principles; "when" the sun should intercepted, "where" the
specific position of the sun during the overheated period and "how" it should be
done (Olgyay, 1957). Thus interpretation of above principles implies the time of the
day during when the maximum solar shading is required, solar altitude which
corresponds the incident angles of solar radiation and the shadow angles when the
maximum shading is required and finally determining the appropriate shading
device for total shade and the correspondence shading geometry respectively.
However, considering incident solar radiation attribute to all angles of incidence to
be covered will invariably yield the shading devices larger than necessary (Dubois,
2000).
3.3.3 Heat Gain through Externally Shaded Window
The solar heat gain through window with external shading devices like,
‘horizontal, vertical and egg-crate devices’ will vary according to the percentage of
glass area under shade and exposed to the sun. Therefore, it is required to determine,
the percentage of the shaded and sunlit areas and the correspondence solar heat gain
97
through each part of the window, in order to evaluate on the performance of fixed
shading devices, for different orientations.
The fraction of window area exposed to the sun (AG) at any time for a given
orientation can be determined by following formula (Kannan, 1991).
a) Continuous Horizontal Projection, fixed at window height level.
AG = [1- OHR (tan VSA)]
(3.42)
b) Continuous Vertical fins fixed at the side of the window
AG = [1- OHRfin (tan HAS)]
(3.43)
c) Egg-crate type
AG =[1-OHR(tan VSA) -OHRfin (tan HAS) + OHR. OHRfin(tan VSA)(tan HAS)]
(3.44)
OHR: is the ratio of the horizontal projection depth (D) and the window
height (Hfen)
OHR = (D)/ (Hfen)
OHRfin: is the ratio of the vertical projection (f) and the window width (Wfen)
OHRfin = (f)/ (Wfen)
Thus, equation (3.10) can be altered to obtain the SHGF for externally shaded
window as follows:
SHGFsh = Ibv (τb + Ni αb) (AG) + k Idiff, v (τdiff + Ni αdiff ) (AG) (W/m2)
(3.45)
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k is the fraction of diffuse radiation obstructed by the shading device.
Hence, the total heat gain (THG) through window is given as:
T.H.Gsh = SHGFsh + U (A) (to – ti)
(W/m2)
(3.46)
A detail analysis of hourly solar heat gain through a 3mm thick normal glass
and for different external overhang depths is discussed in Chapter 5.
3.3.4 Effectiveness of External Shading Device
The primary design principle of the shading device is to eliminate unwanted
solar radiation penetration into the building. The external shading devices are used
to eliminate the beam component and reduce the diffuse component (sky & reflected)
of the solar radiation. Total prevention of solar radiation approaching the building
may cause in reducing amount of daylight intensity inside a building in tropical
climate. But in equatorial tropical climate, effectiveness of shading device depends
on the shading performance during over heated period and on amount of daylight
penetration into the building. Therefore, efficiency of a shading device should be
judged on its relative balance between “shading performance” and the “daylight
efficiency”. Reduction in solar radiation penetration and on daylight, directly affect
on the energy consumption for cooling and lighting respectively. In this respect it
can be argued that the effectiveness of shading device can be best determined by its
energy performances.
Olgyay (1963) suggested that colour, material, location of the shading
protection and specific shading methods influenced the effectiveness of a shading
device. This general classification was made to all types of shading strategies
(glazing, internal and external). Hassan, KAKU (1996) added depth of shading
projection as another aspect that determines the effectiveness of the external shading
strategies. Olgyay (1963) also used shading coefficient (defined in following
paragraphs) as a measurement to determine the effectiveness of different shading
devices.
99
Based on above classification and on further literature review, the factors
affecting on the effectiveness of external horizontal shading devices are discussed as
follows: geometry of the external shading device, surface properties and colour,
location of the external shading projection, effectiveness of different shading
methods and shading device optical properties.
3.3.5 Factors Affecting the Effectiveness of Shading Device
3.3.5.1 Geometry of External Shading Device
The geometry of external horizontal shading device depends on three
dimensions namely; the depth, width and the angle of the shading device (Jorge et al,
1993). Each of these parameters depends on the amount of solar radiation incident
on the fenestration, angle of incident, on how much shade is required on the
fenestration and also on size of the fenestration.
a)
Depth
The depth of a shading device is a function of the window height and angle
requirements of incident radiation which in turn are determined by the latitude and
orientation of particular location. The depth of external shading device is an
effective measure to eliminate solar radiation penetration in low latitudinal locations,
between the tropics. The depth of the device is often described as dimensionless
proportional relationship to the fenestration height (from sill to top plate), which is
defined as ‘overhang ratio’ (OHR). This also defined as ‘projection factor’ (PF) for
the particular window (figure 3.17).
Hassan, KAKU (1996) experimented the effect of depth of the horizontal,
vertical and egg-crate devices on the incident solar radiation (direct, diffused and
ground reflected). Raeissi and Taheri (1997) also experimented on the effect of
overhang ratio (overhang depth to window height) on the cooling and heating energy
100
consumptions. The experiment by Raeissi and Taheri (1997) determined an
optimum overhang ratio 0.6 on the north window and 1.0 on the east and west which
balances the cooling and heating loads for both orientations during winter and
summer. Depending on the location, many countries have adapted the shading
coefficient as a measurement of solar energy transmission for different overhang
ratios.
Overhang Ratio (OHR) = Depth of overhang (D) / Fenestration height (Hfen)
OHR = D / Hfen
(3.47)
D
h2
Hfen
h1
Figure 3.17: Relationship between external overhang depth, window height and
overhang ratio
Literature review also indicated (Olgyay, 1957; Harkness, 1978; Sharifah
2001) depth of the shading device is determined by the incident angle of the direct
solar radiation. This inevitably resulted in large overhang depths. It is important to
understand that only fraction of incident radiation is transmitted through the
fenestration system (shading and glazing) and the other part of it reflects back to the
out side atmosphere (Dubois, 2000; Kuhn, 2000). Therefore it is important to
determine the overhang depth considering the total transmittance radiation according
to specific times of the year. Robbins (1986) also argued that increase in overhang
depth may reduce the daylight penetration through the aperture. However, there is
101
no literature found determining the overhang depth based on daylight availability and
their effect on cooling and lighting energy consumption.
A range of overhang depths were selected to determine which of the shading
hypothesis was optimum in terms of terminating the maximum solar heat gain from
direct solar radiation. The depth of the overhang was determined based on the solar
transmittance property of glazing and the incident angle of direct solar radiation with
special reference to Kuala Lumpur hot and humid tropical climate (Appendix C3).
The critical time period when shading is required was assumed as from 9:00 am to
17:00 pm. Table 3.3 summarizes the correspondence optimum overhang ratio
obtained for main cardinal orientations. These overhang ratios were assumed as to
provide maximum shading by preventing maximum amount of solar heat gain from
direct solar radiation into the building under Malaysian sky conditions.
Table 3.3: Optimum overhang ratio to intercept maximum direct incident solar
radiation; Latitude: 3.120, Longitude: + 101.60- East, West, North and South
b)
Orientation
Overhang Ratio
(OHR=D/ Hfen)
East
1.6
West
2.04>OHR>1.9
North
0.8>OHR>0.7
South
0.6>OHR>0.5
Width
The width of shading device is a function of the window width and angle
requirements of incident radiation. Harkness (1978) and Szokolay (1996) showed a
direct relationship between the overhang depth and the width using correspondence
horizontal shadow angles (HSA) for that particular moment. The lateral extension on
the width of the device is often described as a dimensionless proportional
relationship to the fenestration width (figure 3.18).
102
Givoni (1998) found that increasing the side projection of the overhang
reduced the solar heat gain through the fenestration compared to the overhang just
above the window opening. Raeissi and Taheri (1997) also showed an optimum side
ratio of 0.2 were able to balance the cooling and heating loads for both winter and
summer on south facing window.
Overhang Ratio (extension) = Side extension of overhang (e)/ Window width (Wfen)
OHRe = e/ Wfen
(3.48)
e
D
e
HSA
Horizontal overhang
projection
HSA
Glazing
Wfen
Window in Plan
Figure 3.18: Overhang ratio for side extension of horizontal shading device
However, there is no literature found on the effect of lateral extension of
overhang on daylight penetration and on the effect on both cooling and lighting
energy consumption.
c)
Angle
Angle refers to the tilt of the external horizontal shading device relative to the
plane of the fenestration. Larger overhang depths were required to terminate direct
solar radiation penetration from low solar altitudes. A similar shading mask can be
achieved with shorter overhang depth by tilting the overhang from the horizontal
plane to a specific angle for that particular moment. This geometrical option is
103
mostly used in adjustable overhang and in awnings (Dubois, 1999). In most cases
sensors are being used to determine the intensity of the solar radiation and the sun
position to effectively eliminate the unwanted solar radiation penetration and
encourage daylight penetration during the under heated period. Tilting the overhang
to reduce the solar heat gain may also reduce the daylight penetration. Therefore, it
is important to determine the optimum angle to achieve balance between solar heat
gain and daylight penetration in order to reduce the annual energy consumption for
cooling and lighting.
Dubois (1999) showed that changing the angle of an awning of a south facing
window in Sweden, had significant effect on the cooling and heating loads during
summer and winter. The results showed by increasing the awning slope from 00 -750
reduced the annual heating demand by 0.8% and increase the annual cooling demand
by 33%. However, there is no literature found on the effect of overhang tilt angle on
solar radiation penetration or on daylight penetration with reference to hot and humid
tropical climates.
3.3.5.2 Surface Properties and Colour
The surface finish and colour of the shading projection have an impact on the
solar transmittance into the building (Olgyay, 1963; Hassan KAKU, 1996; Givoni,
1998; Dubois, 1999). The absorptivity and reflectivity of the shading device
depends on the colour of the surface. According to literature, many authors agree
that light colour on shading device reflect and increase solar transmittance than dark
colour devices.
Studies by Dubois (1999) showed that the dark colour (low solar
transmittance) yield a lower annual energy than the light colour awning. The reason
has been that heat transmittance largely affects the cooling load more than on heating
load.
104
In another study, Kapur (2003) demonstrated that there is a temperature
variation on the surface of an externally shaded window glazing. The results also
showed that the dark colour sunshades caused an increase of 30-70C while light
colour sunshade caused an increase of 20-50C in the glass surface temperature during
the day.
Apart from heat transmittance, the surface properties and colour of a shading
device are significant factors for daylight reflectance (Dubois, 2001; Chavez, 1989).
The reflectivity of a surface determines its response to daylight striking on it and the
amount of daylight being reflected.
3.3.5.3 Location of Shading Device
The fixing methods of an external shading device can be categorized as;
attached or detached to the building skin, just over the window (or vertical frame for
vertical fins), leaving a gap between the edge of the window and the shading device.
With an attached shading device, the absorbed heat by the shade may be trapped
between the shading projection and the window surface which may transfer back into
the building. In contrast, detached shading will provide free air movement between
the shading device and the window. Thus the effect of trapped heat can be reduced.
This may have a significant effect on the cooling load reduction.
Adding a vertical gap between the window top edge and the bottom of the
overhang location (h2) will effect on the shading depth of the device (figure 3.17).
Thus the gap will be added to the window height, which will also shade part of the
wall above the window. The advantage of such a gap is that it will give a larger view
of the sky component which is a determinant factor for daylight distribution inside
the building. However, the gap between window edges to shading device will result
in deeper shading projection than a fixed just above window, in order to obtain the
same effectiveness of the external horizontal shading.
105
Experiment by Raeissi and Taheri (1997) found that vertical spacing between
top of the window and the overhang had no significant impact on the annual cooling
and heating energy. The study also suggests that overhang spacing are more
beneficial in higher latitudes than lower latitudes.
3.3.5.4 Effectiveness of Different External Horizontal Shading Methods
The shading mask provides information about the distinctive shading pattern
required to eliminate the unwanted solar radiation during the overheated period.
However the same shading mask pattern can be obtained with different design
options of shading device. This implies that there is no unique solution for the
design of sun breakers. Olgyay (1957) illustrated various characteristics of typical
devices. The same shading effect of solid horizontal overhang can be illustrated
using; overhang partially solid - partially louvered, louvers parallel to wall,
horizontal louvers, etc.
In practice the shading device is determined by the cut off line to eliminate
direct solar radiation. However the amount of solar transmittance may change
depending on the amount of diffuse and reflective solar radiation transmittance.
Therefore the effectiveness of different shading devices is determined by the shading
method. Uses of different methods are influenced by orientation and the solar
altitude. Also it is important to consider the daylight transmittance for various
shading types which may have adverse effects or support daylight distribution into
the interior. Effect on glare control and view out are other dependent factors that
need attention before deciding on the shading device method. Applications of
various types of shading device have different implication on the amount of solar
heat gain into the building. The thermal and optical properties of solar radiation are
wavelength and angle dependent. Therefore, with different shading systems amount
of solar radiation transmitted varies.
106
3.3.5.5 Shading Device Optical Properties
a)
Shading Coefficient
Shading coefficient (SC) concept has been a well established method used to
compare the effectiveness of different solar shading systems (Olgyay, 1963; Kannan,
1991). The ratio of the solar heat gain due to transmittance as well as retransmitted
part of the absorbed radiation of a given window system (glass & shading) to that of
solar heat gain by an un-shaded single pane clear glass (3 mm thick standard)
window is defined as the shading coefficient of that window system (Kannan, 1991).
SC = Solar heat gain of any glass and shading combination
(3.49)
Solar heat gain through a 3mm un-shaded clear glass
In case of different glazing types are being used other than the standard 3mm
thick clear glass or/ and the window is combined with internal or external shading
devices, the respective solar heat gain through each component of the system need to
be determined. Thus, the net shading coefficient for the system (window glazing &
shading device) can be obtained by multiplying the shading coefficients of each
component.
SC system = SC clearglass x SC shadingdevice
(3.50)
Where SC clearglass is the shading coefficient for standard 3 mm thick clear
glass and SC shadingdevice is the shading coefficient of the correspondence shading
device.
The integrated shading coefficient values were obtained for near normal
angle of incidence, but in real context the SC vary with the incident angle of the solar
radiation impinge on a vertical surface.
The SC values for fixed shading devices like ‘horizontal, vertical and eggcrate devices’ will vary according to the percentage of glass area under shade and
107
exposed to the sun. Therefore it is required to determine, the percentage of the
shaded and sunlit areas and the corresponding solar heat gain through each part of
the window, in order to evaluate on the performance of fixed shading devices, for
different orientations.
The fraction of window area exposed to the sun at any time for a given
orientation can be obtained from equations (3.42), (3.43), and (3.44). Once the
fraction of exposed area was determined, the net shading coefficient for a particular
shaded window (SC’) can easily be obtained by the formula (Kannan, 1991):
SC’ = (AG * Ídr ) + fr (A * Ídf)
(3.51)
A x Ítot
SC’: Net shading coefficient for partially shaded window.
Ítot: Total (direct + diffuse) solar radiation transmitted through standard 3mm
clear glass for particular orientation.
Ídr: Direct solar radiation transmitted through standard 3mm clear glass
for particular orientation.
Ídf: Diffuse solar radiation transmitted through standard 3mm clear glass
for particular orientation.
Asun: Area of window exposed to the sun
A: Total window area
fr: Fraction of diffuse radiation obstructed by the shading device.
One of the main draw back in calculating the shading coefficient of a shading
device is that comparison was done to heat gain already inside the building. Also,
only the radiative heat is considered and the thermal heat transmission is not added in
the calculation. Further, the amount of solar radiation transmitted and retransmitted
through window do not take into consideration the amount of heat gain and lose due
to the window frames and edges. Therefore it may be argued that a total shading
coefficient value of the window system needs to incorporate thermal transmittance of
the frames and edges as well. Although, shading coefficient values for external solar
108
shading were specified in the MS 1525:2001 (code of practice for non-residential
buildings on energy efficiency and use of renewable energy), there is a need for
further research in the study of shading devices under Malaysian climatic conditions.
b)
Optical Transmittance
Optical transmittance of a shaded window can be defined as the fraction of
incident solar radiation which passes through an entire window system at a specified
angle. The ratio value is expressed as ‘solar heat gain coefficient’ (SHGC) or Gvalue (g-for gain) for that specific component. The word “system” is used to define
the window and the shading device if applicable as one unit. The total transmittance
of the window glass and the shading device can be expressed as (Dubois, 2000):
Gsys
Gsys
=
Total Solar Energy Transmittance
Incidence Solar Radiation on the facade
(3.52)
=
Ítot
IG* Aw
(3.53)
Hence the total solar energy transmittance of the system (window glazing &
shading device) is a product of the transmittance of each component of the system,
the net G value for the system can be obtained by multiplying the G-value for each
component. Thus it may be expressed as below:
Gsystem = Gwindow x Gsunshade
(3.54)
Gwindow is the G-value for window and Gsunshade is the G-value for the
corresponding shading device. Effectiveness of the G-value depends on how much
solar radiation is transmitted into the building. Similar to the shading coefficient
concept, a shading device with a high G-value is considered to be a ‘poor’ shading
device, since a large proportion of the incidence radiance is transmitted into the
building. Similarly a low G-value indicates a ‘good’ shading device, since a small
portion of incidence radiation is transmitted and retransmitted into the building.
109
Surfaces also emit long wave solar radiant energy according to its emissivity.
This particular surface property is independent of the colour of the surface. The
specula surfaces have very low emissivity than the diffuse matt surfaces.
Also review shows that use of incident angle to determine the shading
geometry yield unrealistically large devices (Dubois, 2000; Olgyay, 1957).
Therefore, a method is developed to determine the external solar shading geometry
depending on the solar transmittance property of glazing and the incident angle of
direct solar radiation with special reference to Kuala Lumpur hot and humid tropical
climates (Appendix C3).
Predicting the effectiveness of a shading device involves in handling of all
parameters that was discussed above. Furthermore, it is not possible to optimize all
criteria simultaneously. As was suggested by literature review, the depth of the
shading device was selected for further experiment. This design variable will look
into the aspects of its influence on solar radiation penetration, daylight penetration
and consequently on the building energy consumption.
3.3.6 External Shading Device and Side-lit Daylight Concept
Several studies have explored the impact of overhang on daylight (Olgyay,
1957; Robbins, 1986; Dubois, 2001b & 2001c; Sharifah, 2004). Main criterion to
use overhang on the window is to limit the unwanted solar gains into the building,
but they also reduce the view of the sky from the room and thus reduce interior
daylight illumination (Olgyay, 1957; Robbins, 1986). Above studies emphasized,
depth of the overhang, surface texture and colour, and position of the overhang fixed
to the window influence the daylight penetration into the building. Robbins (1986)
and Moor (1993) suggested that when overhang is applied, the depth of the room
begins at the edge of the overhang and the location of the window wall merely
defines the usable portion of the space below the roof (figure 3.19).
110
Figure 3.19:
Effect of overhang on daylight distribution in a room
The side-lit strategy for filtering the daylight into the building manipulates
the vertical wall of the envelope of the building. Side-lit produces a strong
directional lighting and non-uniform daylight distribution from the vertical opening
of the exterior envelope to the deeper end of the building (Robbins, 1986). The
penetration of daylight into a room through wall opening depict a relative change in
the quantity of light as it moves deeper into the correspondence space. The daylight
distribution pattern illuminates the horizontal plane of a room as well as the vertical
planes of the correspondence space. The position of the vertical opening enables us
to determine the illuminance distribution along the horizontal and vertical surfaces.
According to Robbins (1986) and Gon (1996) the successful performance of side-lit
concept depends on:
o the amount of daylight distribution
o the room geometry; floor-to-ceiling height, depth of the room and width of
the room
o the size of the window
o the internal surface properties and colour
o the control of direct sunlight penetration onto the work plane and minimize
heat gains
o the control of brightness contrast within the occupant visual field
111
o minimize impact of glare on work plane resulting from high window
placement
The amount of natural light entering the building through window is
attributed from different sources such as, the sky, the ground, exterior and interior
reflecting surfaces. Contribution of each component is more or less important
depending on the sky condition and surrounding exterior environment. In daylight
designs, direct sunlight has been avoided as source of light in building. This is
mainly due to visual discomfort resulting from over illumination, inappropriate
distribution of light into the space and also as a means of energy saving in cooling
loads especially in tropical climates. In this respect, the common design solutions to
control solar heat gain are use of smaller glazing areas and use of shading devices.
However, the smaller glazing reduces view out as well as the light levels (Dubois,
2001c). Also extensive use of solar shading may reduce the daylight penetration
which will increase the use of artificial lighting (Abdullah-Abdulmohsen, 1995;
Robbins, 1986). Hence, it is important to point out that geometry of the external
solar shading is a crucial consideration in energy saving in buildings due to daylight
utilization.
3.3.6.1 Adequate Illuminance on the Work Surface
The lighting quantity is a major requirement to ensure good visibility and
visual performance. The minimum level of indoor illuminance depends primarily on
the nature of the task or interior location. The illuminating engineers society of
North America (IES, 1993) recommends to maintain illuminance level at/or below
500 lux on the horizontal work plain, for offices containing computer screens. The
study of Berrutto et.al (1997) indicated an average preferred horizontal illuminance
of 325 lux for computer work and 425-500 lux for general office work.
The Malaysian standards-MS 1525 (2001) recommended a horizontal
illuminance of 300-400 lux for reading, writing and drawing in general offices. For
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infrequent reading and writing the standard requirement is 200 lux. According to
this standard, the illuminance should not be below 200 lux at any point in the room.
Further, for task work like proof reading recommended illuminance level is 500 lux
while for exact drawing, and detail work the standards were 1000 lux and 2000 lux
respectively. But, the first government low energy office (MEWC-LEO 2004)
building in Putrajaya, Malaysia, reduced the target indoor illuminance from 500lux
to 335 lux as a measure of energy efficient feature (Kristensen, 2003). As the
building is still under experiment it is difficult to determine the effect of reducing the
illuminance level on overall energy saving.
Table3.4:
Recommended average illuminance levels for office buildings
Source
Illuminating Engineers
Society of North
America (IES, 1993)
Berrutto et.al (1997)
MS 1525 (2001)
Dubois (2001c)
Illuminance
(lux)
500
325
425-500
200
300-400
300-400
500
<100
100-300
300-500
>500
MEWC-LEO Building
Putra-Jaya (2004)
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Example of Application
- General reading and writting
- Ideal for computer work
- General office work
- Infrequent reading and writting
- General reading and wrtting
- Drawing office
- Proof reading
- Too dark for paper and computer work
- Too dark for paper work/acceptable for
computer work
- Acceptable for paper work/ideal for
computer work
- Ideal for paper work/ too bright for
computer work
- General reading
3.3.6.2 Daylight Factor (DF) and Sun Illuminance Ratio (SIR)
The daylight factor (DF) and sun illuminance ratio (SIR) are two primary
dependent variables related to interior illuminance level. However, most techniques
for evaluating the potential of a building design to provide adequate internal
illuminance using natural lighting are based on the calculation of daylight factors. A
daylight factor is defined as the ratio between interior illuminance (Ei) and the
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exterior illuminance (Eo) on a horizontal surface simultaneously available out doors
from an overcast sky (Robbins, 1986).
Daylight Factor (DF) = Ei/Eo x 100
(3.55)
Daylight factor technique calculates three components of illuminance: the
light direct from the sky vault (Edsky), external reflected component (Er(ext)sky) and
internal reflected component (Er(int)sky).
Daylight Factor (DF) = (Edsky + Er(ext)sky + Er(int)sky ) x Cg x Cf x Cd (3.56)
These three components are multiplied by compensation factors for glazing
type (Cg), window framing (Cf) and window dirt (Cd), to represent the reduction in
interior illuminance due to the above factors (Robbins, 1986). Then DF in equation
(3.55) can be re-written as:
Daylight Factor (DF) =
{Eidsky + Eir(int)sky} x 100
(3.57)
Eo,sky
The DF can be used to indicate the potential for daylight utilization of a
building or space. Since the DF is the ratio of indoor to outdoor illuminance, the
ideal approach is to obtain the DF for the desired illuminance when the sky is at
lowest brightness. According to Bremen (1969) the lowest exterior horizontal
diffuse illuminance from sky for humid tropical climate is around 10,000 lux (table
3.5). Hence, to obtain a 200 lux minimum illuminance, a daylight factor of at least
2% is required. To provide sufficient work plain illuminance of 500 lux as
recommended by the Malaysian standards (MS 1525:2001) a daylight factor of 5%
must be obtained. These values are considered as the desirable daylight factor (DF)
target range.
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Table 3.5: Standard lowest exterior diffuse illuminance (lux) from Sky for
different climatic regions. Source: Bremen, H. van (1969)
Standard Lowest Exterior Diffuse
Illuminance from Sky (lux)
5000 lux
10,000 lux
20,000 lux
Climate Region
Temperate & Cold Climate
Humid Tropic
Hot/ Arid
The sun illuminance ratio (SIR) is thus defined as, the internal total
illuminance, from the direct sunlight and the reflected illuminance from sunlight on a
horizontal surface to the exterior sunlight illuminance.
Sun Illuminance Ratio (SIR) = Direct Illuminance Sun + Reflected Illuminance Sun
Exterior Illuminance Sun
Sun Illuminance Ratio (SIR) =
Eidsun + Eirsun
(3.58)
Eo,sun
Although use of DF to determine the interior lighting level has been well
established, according to Hamdan (1996) it is questionable to use the DF under
overcast skies in hot humid tropical conditions like in Malaysia. The other major
limitation is that it does not take into account of the direct component of the sunlight.
The internal total illuminance on correspondence station point is a major influence in
reducing the energy for artificial lighting. The internal total illuminance is the sum
of direct illuminance from sky, reflected illuminance from sky, direct illuminance
from sun and reflected illuminance from sun on an interior horizontal surface.
If the required daylight factor (DF) and sun illuminance ratio (SIR) and the
exterior illuminance conditions for a particular location are known, then the internal
absolute illuminance can be obtained as follows:
From equation 3.57
Eidsky + Eir(int)sky = (DF) x Eo,sky
(3.59)
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From equation 3.58
Eidsun + Eirsun
= (SIR) x Eo,sun
(3.60)
Hence, absolute illuminance at interior will be the addition of equation 3.59
and 3.60:
(Eidsky + Eir(int)sky )+ (Eidsun + Eirsun ) = {(DF) x Eo,sky}+{(SIR) x Eo,sun}
(3.61)
Where, Eo,sky and Eo,sun are exterior horizontal illuminance due to diffuse
light from sky and external horizontal illuminance due to direct sunlight respectively.
Hence, DF and SIR are expressed as a ratio of the interior and the exterior
illuminances, thus they are relative measures and not an absolute measure of
illuminance. The relative internal illuminance striking at a given station point
consists of four components of natural lighting illuminances (LBNL, 2003b):
o Direct illuminance of the sky (Eidsky): the light which originates in the sky
and reaches the reference point without reflection from the interior surfaces
of the space. In addition this includes the reflection of sky light from exterior
building shades, sky light reflected from the ground and sky light reflected
from exterior obstructions.
o Reflected illuminance of the sky (Eir(int)sky): the daylight which originates in
the sky and reaches the reference point after reflecting from the interior
surfaces of the space.
o Direct illuminance of the sun (Eidsun): the light from the sun reaching the
reference point without reflection from the interior surfaces of the space.
o Reflected illuminance of the sun (Eirsun): the sunlight which reflects from
interior surfaces before reaching the reference point.
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3.3.6.3 Daylight –Electric Light Integration
CIBS Code (1984) for interior lighting underline three basic fundamental
decisions for integration between daylight and electric lighting in the building
design:
i. To rely on daylight during daytime and to design the electric lighting only for
night time conditions
ii. To use daylight as available and supplement it as required by electric lighting
iii. To ignore daylight and operate the building on electric light only
The first method appears to be the best way to achieve energy saving for
lighting, but it depends on the amount of daylight throughout the day-time. This is
not possible all the time as it is difficult to obtain constant daylight level throughout
the day, where daylight level fluctuates depending on various other factors. On the
other hand, total depend on electric lighting may cause on high energy consumption
for lighting as well for cooling due to the heat generated by the artificial lighting
system. In this case introduction of energy efficient light sources may be an option
to achieve low energy consumptions.
As for the second method, more daylight in interior spaces only leads to
electrical energy savings if the artificial lighting is controlled according to the
amount of daylight penetrating into the room. In order to establish a suitable
electrical lighting control system for a day-lit building, three aspects need to be
analyzed: the lighting zone to be controlled, occupancy pattern of the space and
control strategy for each zone (Chavez, 1989).
a)
Lighting Control Zones
As with side-lit concept, daylight illuminance decreases with the increase
distance from the opening towards the deep end of the space considered. Therefore
supplementary lighting is required to provide required task, background or general
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illuminance. The criteria to establish the integrated lighting control zone need to be
based on consideration of user activities, position of work station compared to
location of the aperture through which daylight is available. A similar approach was
developed through ‘PSALI’ or permanent supplementary artificial lighting of
interiors, which provides additional lighting at the back of a space to balance the
brightness of a given aperture (Hopkinson and Kay, 1969).
b)
Occupancy Pattern
The occupancy pattern is defined by the density of users and the character of
the activities they carry out in a given building. As discussed in section 3.2.2.5,
generally there are four basic types of occupancy patterns. Occupancy schedules are
major determinant factor of lighting, equipment and air-conditioning loads. In
developing occupancy schedules, it can be useful to group together individual spaces
with similar occupancy characteristics (Moore, 1993). An energy management
system can be used to control lighting on pre-determined occupancy schedule.
c)
Control Strategy
Principally there are two different ways of controlling the artificial lighting:
manual control system and automatic control strategy. In general lighting control
systems can be operated based on different parameters of the lighting installation:
amount of light level (either in illuminance or luminance), light distribution and on
spectral distribution.
In manual control system the user switch on the artificial lighting when the
daylight is inadequate to perform particular visual tasks (e.g. reading, writing,
drawing or any typical office work) or when the interior looks gloomy and switch off
when the required daylight level is adequate (Chavez, 1989). In this instance, the
occupants’ knowledge on daylight levels and energy implications are important
aspects (Crisp, V. 1977). One major draw back in using the manual control systems
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is that getting the user into the habit of switching the lights off when not required is
not easy. It is required in order to save unnecessary energy consumption for lighting.
The automatic lighting control strategy is classified into two control systems:
Automatic switching and dimming system. The automatic switching on/off is made
by means of sensing the presence of occupants and by photoelectric sensing of
available daylight level. This system is also called two-step switching and the light
output varies in discrete and equally spaced steps (Robbins, 1986).
The control action by photoelectric dimming system can be explained as the
electric output decrease continuously as the daylight illuminance increases. Two
basic automated dimming systems exist: linear continuous dimming and
continuous/off dimming system. In linear continuous dimming system, after
achieving the required illuminance level, the electric power output remains constant
as the daylight illuminance increases. Similarly, in continuous/ off strategy, the
lights turn off completely when the total illuminance (electric illuminance and
daylight illuminance) exceeds the required interior illuminance level. The energy
saving potentials (minimum use of electric light, reduce the lighting load and cooling
load) of the continuous/ off dimming strategy is greater than the other options
discussed and more likely acceptable to occupants (Chavez, 1989). Also, the electric
lighting in the room is changed in direct response to the level of interior daylight
illuminance. Yet, the complex electronic control system, high installation and
maintenance cost are a major hindrance. In this respect the continuous/ off control
system is suggested as a better daylight –electric light control strategy to implement
as energy efficient measures. Further, same author suggests that suitable control
option should be chosen as a function of daylight availability. Thus explained as
follows:
o When daylight level is inadequate to meet the required level, dimming is
suggested
o If daylight level exceeds the amount required, switching off and dimming
system is recommended
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o If enough daylight is available on most hours of the day, switching off or
continuous/off system is recommended
Hence, the review suggests that the interplay of daylight availability and the
occupancy pattern are determinant factors in selecting an appropriate lighting control
system.
3.3.7 Research on Solar Shading
Many researches and experiments on solar shading have been carried out
under different climate conditions and on its performance as a building element.
From review it is found that researches on shading strategies can be categorize into:
I. Shading strategies and solar radiation
II. Shading strategies and daylight
III. Solar shading and energy related experiments
IV. Solar shading design methods
V. Solar shading and human perception
3.3.7.1 Shading Strategies and Solar Radiation
Studies on impact of solar shading strategies on solar radiation penetration
have been expressed in terms of incident radiation, solar transmittance, reflectance,
solar heat gain factor (SHGF) and shading coefficient (SC) (Dubois, 2000).
Initial experiments done by Olgyay and Olgyay (1957) have been a very
important literature on the subject of shading device. The study involved in different
glazing types ( ordinary clear glass, dark and light color plate glasses, double pane
glasses), internal shades and external shades and their impact on the heat gains. The
results showed that different glazing types reduced the heat gain by 25-50%, internal
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shades and blinds reduced 50% and external shades by 59% compared to heat gain
through ordinary clear glazing. The study indicated a broad classification of shading
devices in respect to their shading coefficient.
Hassan KAKU (1996) experimented on the effect of external shading devices
for buildings in Malaysia. Key findings indicated horizontal devices generally are
more effective against high sun at east and west orientations, while egg-crate devices
for all orientations. According to results the egg-crate device eliminated 57% of the
solar input at west orientation as compared to 46% and 10% by the horizontal and
vertical shading devices respectively. The study emphasized further that the shading
performance of each device with respect to different solar radiation components;
direct, diffuse and reflected. The study also concluded that the contribution of
diffused and reflected radiations with respect to the total solar gain was
proportionally significant in hot-humid conditions. Similar studies by Givoni (1998)
indicated external solar shading devices can eliminate 90% of striking solar radiation
and more effective than internal shading devices. The provision of ground
reflectivity and effect of colors on shading devices were also considered as important
aspects in determining the effectiveness of the shading device (Hassan KAKU,
1996).
Several works (Bülow-Hübe, 2002; Dubois, 2000 and Kuhun et al, 2000) on
defining solar shading devices considering the total solar energy transmittance (gvalue or solar heat gain coefficient) were carried out. This method provides a more
realistic approach to evaluate the effectiveness of internal and external shading
devices in combination with glazing of the correspondent window (Kuhun et al,
2000). Bülow-Hübe (2002), studied the transmittance value (g-value) based on
actual measurements taken for external devices (awnings, Venetian blinds, screen
fabric, horizontal slatted baffle and solar control films), inter-pane devices (Venetian
blind, pleated curtains, roller blind and screen fabric) and internal devices (Venetian
blinds, pleated curtains, roller blinds, screen fabric and solar control films). The
results showed an average g-value of 0.3 which indicated only 30% of incident solar
radiation was transmitted through external devices. Similarly g-value of 0.5 and 0.6
indicated that 50% and 60% of incident solar radiation was transmitted through inter-
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pane devices and internal devices respectively. This value explains that low
transmittance value shading devices had better shading strategy while high
transmittance values had a poor shading strategy. However, the experiments were
carried out under temperate climate, in Sweden.
A study by Sharifah and Sia (2001), with reference to Penang (Latitude 5.30
N & Longitude 100.30 E) suggested the provision of horizontal solar shading devices
on the window opening for main cardinal and other related orientations. The
calculations were made corresponding to critical hour interval between 10.00 hr and
15.00hr of the day, in order to eliminate the direct solar radiation incident on the
vertical surface, (window panes). Also the study concludes that the orientation of the
window is a deciding factor on the shading device geometry. However, the study did
not calculate the reduction of striking solar radiation.
3.3.7.2 Shading Strategies and Daylight
Olgyay and Olgyay (1957) introduced a method to calculate the daylight
efficiency when external shading devices were applied. The daylight efficiency was
determined by the ratio between the daylight amount entering through an opening
with and without a shading device. According to the calculations for a horizontal
device overhang ratio (horizontal projection / window height) of value 1 reduced
60% of daylight penetration. The calculations were made based on several
assumptions; the sky has equal luminance of radiation, no reflection were considered
and projections were assumed to be long that light entering from sides were
neglected. Further, the above method did not calculate any daylight distribution and
only suggest how much light is cutoff by the shading device.
Sharifah and Sia (2004) showed that use of appropriate shading depths to
reduce the direct sunlight penetrations reduce the daylight factor by 50%. Further,
without shading, daylight factor of the interior ranges between 6% and 2% from the
aperture to deep end of the space. This was obtained under a bright sunny day.
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However the study did not give a clear indication of amount of solar heat gain and
daylight distribution when sunlight control strategies were applied.
Studies carried out by Azni Zain-Ahmed et al. (2002) on daylight and
window to wall ratio (WWR) indicated an optimum WWR for appropriate daylight
for Malaysian climate. The findings indicated the optimum window opening for
daylight was 25% of window to wall ratio. The same window to wall ratio received
solar heat of about 1460 W/m2. The study was done using a computer simulation
program called the NORMA. Yet the experiment did not explore the impact
between shading devices (and their corresponding shading coefficients) and daylight
distributions under Malaysian climatic conditions.
Hamdan (1996) experimented daylight distribution on side lit atria in hot
humid tropical sky conditions. The results yield a significant reduction in daylight
level within the side lit atrium space compared to top lit concept. But the resultant
daylight was adequately provided on the optimum distance between the clerestory
walls for the purpose intended of the space. This enabled on saving energy by
minimizing the use of artificial lighting. Thus, cooling load was minimized as heat
from direct sunlight was blocked.
Relationship between the shading device, daylight quality and energy use
were investigated by Dubois (2001c). The experiments were carried out using two
methods. Firstly, actual field measurements were taken using an actual size office
room and secondly, using a computer simulation program. The selected shading
devices for the first experiment were mainly solar screens with color variations of
black, brown and white including one Venetian blind. The second experiment used
Venetian blind (00 & 450 slat angle), awnings, screens and a single overhang with
slats to evaluate the daylight quality. The comparison between the two methods
yields almost similar results for the screen and Venetian blinds (white color). Yet
the experiment was carried out under temperate climate conditions in Denmark and
for a single orientation (south). Results indicated grey screens and 450 slats for
Venetian blind yield too little daylight (less than 300lux). The bare window, white
awning, overhang and 00 slats for Venetian blind provided high illuminance value for
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computer work and were recommended for paper works. Also the same group of
shading devices generated luminance values above 500cd/m2. Further, dark colored
devices resulted in unacceptably low work plane illuminance (about 100 lux) even
under clear sky of 65-95klux global illuminance. Likewise, results on daylight
factor appeared to be well below 1%, thus indicated that artificial lighting may even
be required even under sunny conditions in Denmark. The simulations were
performed using the ‘radiance computer simulation program’ for the sunny sky
conditions. Also the implication on the energy is limited to a manual switch on
probability. Hence the study did not determine the absolute energy saving.
Robbins (1986) graphically illustrated the impact on daylight penetration and
distribution in a room for different overhang ratios and light shelf configurations.
The overall findings showed that increase in shading depth reduced the daylight
penetration into the deep end of the room. The study gave a conceptual idea and
general knowledge on daylight related issues, which can be applied as basics in
daylight designs. But the study did not indicate an optimal shading strategy for
minimum daylight level for any particular climate.
Al-Shareef (2001) studied the daylight performance using a parallel shading
system for hot and arid climates. The results indicated the impact of shading system,
especially the slat reflectance and the slat angle on the daylight quantity. A reduction
of 50% reflectance caused 70% to 80% of illuminance reduction. Further, the slat
angle 150 gave a better daylight distribution than other angles considered. However
the conclusions did not predict results on solar heat gain effect and energy utilization.
Studies by Perera et al (2001) on the impact of different glazing types on
daylight distribution under diffuse sky for hot and humid climate conditions in Sri
Lanka showed almost 90% reduction in illuminance level occurred with reflected
glazing compared to clear glass. Similar studies by Dinapradipta et al (2003) in
Indonesia concluded, those effective room depths for tinted and reflective glazing for
minimum daylight illuminance respectively to be 4.6 and 3.1meters.
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Garcia-Chavez (1989) and Abdullah Abdulmohsen (1995) experimented with
the potential of light shelf on daylight distribution and energy consumption for hot
and arid climate. Experiment by Garcia-Chavez (1989) explained some valuable
findings and developed a guideline for beam core day-lighting application in hot and
arid region of Mexico. The study concluded that the internal light shelf can
distribute daylight deeper than the external light shelf. Also the study found that
combined light shelf with double openings can reflect the light 10 to 12 meters away
from the external aperture. Similarly, Abdullah Abdulmohsen (1995) concluded that
a combined light shelf system provides adequate illuminance levels, and uniform
distribution illuminance as well reduced the glare through the window. According to
his results, the optimum light shelf depth for a south facing window had an external
light shelf depth of three times the height of view aperture and internal device was
twice the height of the view aperture. The energy calculation also confirmed that
best energy savings were obtained for the above stated light shelf configurations.
The experiment by Garcia-Chavez (1989) was done in an actual building while
Abdullah Abdulmohsen (1995) used a scale model.
3.3.7.3 Solar Shading and Energy Related Experiments
Parametric studies on energy use were investigated by using solar protective
glazing and seasonal awnings, in two separate experiments done by Dubois (1998 &
1999). The experiments were carried out in Sweden where solar heat is a favorable
aspect to reduce energy consumption for heating during the cold seasons. Impact of
glazing u-value on thermal gains and losses were investigated. The study predicted
the annual energy use in terms of cooling and heating loads. With a glazing-towindow area of 30% on the south façade indicated a lower energy use with clear and
low-e coated glazing, than on other orientations. Further, changes of orientation
reduced cooling load by 58% and heating load was reduced by 23%. Yet, changes of
glazing types from shading coefficient 0.86 to 0.16 reduced the cooling load by 86%
and heating load by 27%. This implied that glazing type was more significant than
the orientation especially for cooling load. Further, higher transmittance glazing
showed a low annual energy, while low-emissivity coated glazing yielded the lowest
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annual energy use. But no relative comparison was done between the two load
consumptions.
In another study by Dubois (1999) on seasonal awning showed a large energy
saving on the cooling load. The results showed 81% reduction of the cooling load
and increase the heating load by 6%. Further, use of awning decreased the annual
energy use by 14%, compared with clear glazing option. The finding also concluded
that the awning depth of 1.25 meters, 300 awning slope and 3.96 meters awning
width obtained an optimum energy saving for cooling and heating. The study further
showed awning colour had a moderate effect on the cooling demand. The results
indicated light coloured fabrics resulted in higher cooling load than dark colour
awnings. Both experiments were done using dynamic energy simulation program
DROB-LTH.
Lee E.S et al (1998) tried to obtain a relationship between the optimum
cooling/ lighting energy and the envelope, using an automated "dynamic" venetian
blind in two side-by-side full scale office rooms in, California, under temperate
climate conditions. The results were tested for static blind angles of 00, 150 and 450.
The average peak cooling load reduction of 6%-15% (for 450 tilt angle) and 18%32% (00 tilt angles) were achieved by the dynamic blind compared to static blind.
Further, compared to the static blind (at any angle) with no daylight control model,
22%-86% of daily lighting energy savings were obtained by the dynamic blinds.
The impact of different glazing types on cooling load were investigated by
Bojic et al (2002) for two high-rise residential buildings in Hong Kong. The findings
showed yearly cooling load reduction of 10% and peak cooling load reduction of
11% when clear glass was replaced by reflective-tinted glasses with shading
coefficient of 0.25 on the west orientation. Analysis on orientation showed, the
yearly cooling load and peak cooling loads reduced by 7% and 11% when the clear
glass façade facing north and south orientations, compared to the west. Further,
difference in cooling load and peak cooling loads showed 13% and 16% reductions
when the building with reflective-tinted glazing was facing the south compared to the
same building facing the west with clear glazing. Thus the findings emphasized that
126
glazing with lower shading coefficients and building orientation significantly effect
on the building cooling and peak loads.
Raeissi and Taheri (1998) studied the optimum overhang dimensions for
cooling and heating dominant buildings, under hot and arid climates in Iran. The
main variables were the overhang depth, overhang side extensions and the overhang
spacing between the bottom of overhang and the top window frame. The experiment
was able to determine an optimum overhang ratio of 0.6 on the north window and 1.0
on east and west which balanced the cooling and heating loads for both during winter
and summer. Further, side extension ratio of 0.2 indicated an optimum energy
saving for the south oriented window. Apart from that vertical distance between the
top of window and the overhang had a negligible effect on the energy saving.
Huang et al (1992) investigated overall energy consumption on lighting load
and cooling load, based on climatic data obtained for Singapore weather conditions.
The study was experimented for prototype office buildings developed for Singapore
comprising a square shape building plan, 'L' shape building plan and rectangular
building plan. The experiment was limited to overhang shading devices (0.33 and 1
overhang ratio-OHR) and different window-to-wall ratio (solar aperture) as the main
variable of daylight and energy consumption. The test was carried out for perimeter
depth of 3.7 meter, 6.1meter and 9.1meter for internal required lighting levels of 323
lux and 528 lux. The results indicated a minimum total energy used was obtained at
solar aperture 20% (WWR x SC). Solar aperture is defined as the window-to-wall
ratio times shading coefficient of the window glass (Huang et.al, 1992). Further
increase of solar aperture progressively reduced the lighting energy saving, while the
cooling energy consumption continued in linear fashion, thus the total energy use
increased. The results were acquired for 6.1meter deep office building with 21.5
W/m2 lighting power for a required lighting level of 538 lux. Similar patterns were
found for 3.7 and 9.1meter deep zones, the minimum energy range rely between 10%
and 20% solar apertures. The experiments did not explore the daylight distribution
and the corresponding heat gains through the window. Also the energy results were
depended on other variables (different illuminance levels, lighting power
127
requirements, window-to-wall ratio) as well, therefore it was difficult to derive clear
conclusion on the effect of solar shading on total energy consumption.
3.3.7.4 Solar Shading Design Methods
Olgyay (1957) and Mazria (1979) developed a shading mask that can be used
to determine the external solar shading device geometry. Mazria’s shading mask is a
rectilinear mask, which coincides with a Cartesian sun-path diagram. Olgyay
developed a hemispherical mask, which coincides with polar coordinate sun-path
plot. Since then the shading mask has been developed into computer based tool and
models that can be used to determine the shading geometry (Shaviv, E, 1975; Jorge
et al, 1993; Arumi-Noe, 1996; Kallblad, K, 1999). Major limitation of these tools is
that they only consider the solar radiation incident on the window and do not
consider the transmitted solar radiation through the window.
Dubois (2000) developed a solar chart using the incident angle dependent
properties and total solar energy transmittance (also called the g-value). She super
imposed the solar transmittance values on Mazria’s solar path, for the temperate
climate. However, this study only considers the south orientation. One of the
limitations of this chart is that for each orientation, we need to prepare corresponding
charts. Further, the study only considered the direct solar radiation to define the
shading device.
Oh, K.W (2000) developed a computer model to calculate the solar radiation
transmittance through an un-shaded window. The model was superimposed on a
solar path diagram in order to determine effective shading device based on the solar
heat transmittance. However these tools need to be validated to be used under any
climatic conditions. Further experiments need to be developed to calculate the
impact of shading devices on daylight and allow prediction of heating, cooling and
lighting. Lack of computer models considering the movable shading devices and
relative calculation methods was considered as disadvantages in his study.
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3.3.7.5 Solar Shading and Human Perception
Several studies were concerned with occupant’s response on solar shading
and the aesthetic expression of shadow casting. A pilot study was carried out by
Bülow-Hübe (2000) on office workers preferences on exterior shading devices.
The shading devices used in this study was awning and venetian blinds. Results
indicated that shading devices were used frequently to avoid glare from the window.
Also a weaker occupant’s response was indicated on the amount of interior
illuminance level, the sunlight patches and how much the shading devices were
pulled down or vice versa.
Belakehal et al (1996) studied the aesthetic expressions of façade created by
solar control shading. The façade surface was divided into different volumes of
projections according to a grid pattern. Each projection was given a mathematical
codification. The study derived a coordinate system for each projection of the façade
for different orientations.
There were no literatures found on aspect such as visual comfort and thermal
comfort when shading strategies were adopted. Comfort is the main issue in any
energy saving approach (Holz et al 1998).
Though it was mentioned in many research works and publication that solar
shading reduces the effect of glare on occupant's perception, there were no clear
conclusions made between solar shading and glare indices. Also review indicated
lack of research on relationship between behavioral studies and the shading device
strategies.
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3.4 Summary
This chapter has discussed the energy pattern and energy related issues in
Malaysian context (in general South East Asian region) to get an overview on the
energy consumption in office buildings. Literature review on energy consumption
pattern in Malaysia revealed energy demand in general has increased almost thrice in
year 2002 compared to year 1990. Thus, it is important to promote energy
conservation and efficiency in every energy consumption sectors in the country in
order to reduce the energy demand in the future. The survey on energy consumption
in non-residential buildings in South East Asian countries revealed that energy
consumption in Malaysia and Singapore commercial buildings were high compared
to other countries in the region. According to the surveyed results, the energy
consumption for air-conditioning and fans was about 68.8% and for electric lighting
is about 23% of the total electricity use, in Malaysian office buildings. As an energy
efficient measure, standards and codes were introduced to determine the baseline to
obtain energy efficiency mainly in non-residential buildings. These standards
underline the minimum requirements to achieve energy savings in buildings.
Review of the related design and theoretical considerations on high-rise
office buildings enable to understand the factors influencing the building energy
consumption. The principles of energy efficiency evaluation of existing buildings
were reviewed by considering the influence of architectural design form and their
interaction with the climatic design parameters, especially with respect to solar
radiation and daylight aspects. Analysis of the theoretical and design consideration
suggested that the representative tropical high-rise build forms included plan
configuration, service core position, floor-to-floor sectional height and building
envelope design options. However, review also revealed that each of these aspects
influence in building energy consumption at various degrees. Since the main focus
of the study was on the effects of external shading strategy on building energy use, it
was recognized the limitation to optimize all design variables simultaneously. Thus,
the study emphasized the complexity of developing a single configuration of high-
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rise office building to represent the climatically interactive high-rise buildings in hot
and humid climates.
The principles of heat gains, types of heat transfer and factors influencing
heat gains in the building were also reviewed. According to the heat source, heat
gains in building can be categorized into two; heat gain through building design
variables and internal sources. The building design variable influenced the
conduction heat gains, heat gains through fenestration and infiltration. Heat gains
from artificial lighting, occupancy heat gains and heat gains from equipment were
the major internal heat sources. Methods to calculate the impact of daylight and
electric light on cooling load due to daylight-electric light integration were presented.
The review will be useful in determining the energy saving potentials due to daylight
utilization in buildings.
Influence of solar heat gain through fenestration on building thermal
performance was discussed. Variables affecting on determining the solar heat gain
factor were emphasized. The review revealed influence of fenestration had a
significant impact on the building thermal performances. The heat gain through
fenestration was determined by the intensity of the incident solar radiation, incident
angle and windows thermal as well as their optical properties. Review also stresses
the importance of obtaining SHGF under local climatic conditions for better energy
calculations. Influences of window’s thermal and optical properties on SHGF were
discussed and SHGF calculations methods were reviewed.
Applications of various types of solar shading devices reduced the impact of
the solar heat gain into the building. Different solar shading devices and factors
influencing the reduction of solar radiation penetration into the building were
reviewed. Thus, the review suggested that external shading strategies give a better
solution for tropical climate condition to eliminate solar radiation penetration than
the internal shading strategies. Designing of solar shading geometry were presented
and limitation of the traditional methods still used in tropical climate regions were
discussed. Factors influencing the effectiveness of the shading device were reviewed
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and a new definition for effectiveness of a shading device was proposed with respect
to solar heat gain reduction, daylight distribution and energy consumption for
cooling and lighting. However, the depth of shading device was selected for further
experiment on its impact on the solar radiation and heat gain, daylight penetration
and on energy consumption.
CHAPTER 4
METHODOLOGY
This chapter is divided into two parts. The first part briefly outlines the need
for the study and development of initial model for the study is discussed (section 4.1
and 4.2). Part two (section 4.3 to 4.8) reviews the energy evaluation methods and
common research methodologies used by previous researchers in order to formulate
an appropriate methodology to be employed in this study. Further, the study
procedures, assumptions, limitations and the overall sequence of the selected
methods are described. Finally, the data analysis criterions are discussed that will be
used to analyze the results of the study.
4.1 The Need for the Experiment
The external horizontal shading device is an important climatic design
element in the tropical climate. According to the review, little is known about the
influence of external horizontal shading device on reducing the solar heat gains,
daylight penetration and the building energy consumption. Another important aspect
is that the review on energy audits indicated a high intensity of energy consumption
(an average of 269kWh/m2) for office buildings in Malaysia. However, significant
energy savings can be achieved in buildings if they are properly design and operated.
Therefore, it is important to investigate the above interrelated issues to determine
appropriate solar shading design strategies for the correspondence climate
conditions. Also, early design decisions are the most effective than making changes
at later stages after construction, which is time consuming and costly.
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4.2 Development of Simplified Office Room Configuration
According to the literature review, energy performance of high-rise building
is influenced by several design variables. The best option to optimize the total
building energy consumption is to test the number of design alternatives, which is
time consuming and laborious approach. The other way of dealing with the problem
is by varying one variable at a time and keeping the others fixed at reasonable
practical values in order to determine the effect of the particular variable on the
energy performance of the building. Therefore, it is necessary to find a compromise
that best matches the priorities and objectives of the study.
As stated in Chapter 1, the main aims of the research are:
a. To assess and compare the impact of external horizontal shading device
geometry in reducing the unwanted solar heat gain and the amount of
daylight penetration into the building.
b. To compare the potential trade-off involved between the solar heat gain and
daylight penetration for determining the optimum overhang depth to achieve
optimum energy consumptions.
Hence, to answer the research questions and to achieve the research
objectives (as stated in Chapter 1) a single zone primary unit office room is selected
for the study. The geometry and characteristics of the typical office room model is
developed based on the analysis of the high-rise office buildings in Malaysia with
following assumptions:
a. The typical office room is in the perimeter zone with a single window.
Hence, assumptions are made that heat gain through the window system is
significant compared to the heat gain through wall, floor and roof area in
high-rise office buildings.
b. Heat transfer from internal walls, ceiling and the floor are constant for all
tested cases.
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c. The prototype office room can be accumulated to create perimeter office
buildings facing the main cardinal orientations.
d. Further, use of perimeter office room will avoid the calculations of the energy
consumed by the building’s deeper spaces and core spaces, which are largely
depending on artificial means for cooling and lighting. These spaces are also
independent from the effects of solar radiation and shading strategies.
4.2.1 Office Room Geometry
The base-case office room geometrical configuration for the present study is
taken as; the height from floor to ceiling to be 2.8 meter (9ft) and width and depth of
the room as 6.0 meter (20ft) (figure 4.1). These measurements are taken in order to
comply with the gross internal area (GIA) of 36m2. The ratio between height, width
and depth is almost 1:2:2, which is the minimum ratio recommended for a day-lit
room, (Littlefair, 1999).
4.2.2 Window Size and Work Plane Height
In this study, the maximum limit of the window area is assumed as 50% of
the internal wall area between the floor and ceiling height. The aperture above the
height of the work plane is assumed to be effective in distributing natural light, while
the area below the window sill has no effect on light distribution on the work plane.
Therefore the window sill height and the work plane height are assumed to be equal.
The window extends from one side of the wall to the other and upward to the ceiling
line (figure 4.1). Hence, the size of the window is 1.82 meter in height (above the
sill up to ceiling line) and 4.4 meter in width.
135
6.0 m (20 ft)
6.0 m (20 ft)
0.9 m (3 ft)
1.82 m
(6 ft)
0.9 m
(3 ft)
External Wall
Floor to ceiling
2.8 m height
(9 ft)
4.4 m (14 ft)
External Window
Internal Wall
Figure 4.1: Base case office room configurations
4.2.3 External Overhang
The external horizontal shading device is the primary independent variable in
this study. The main purpose of this study is to determine the effectiveness of the
use of external horizontal shading device in terms of reducing solar heat gain and
achieving target illuminance level in order to obtain optimum annual energy use.
Thus, the following assumptions are made to determine the shading strategy:
a. Critical over heated period during the day time is considered as from 9:00 am
to 17:00 pm.
b. More than 80% reduction in incident direct solar radiation is considered as
maximum shading. (For most ordinary glazing about 80% of the incident
solar radiation is transmittanced around the normal to the window)
c. The overhang is extended on either side of the window (figure 4.2).
Therefore solar radiation and daylight entering from the side of window is
neglected.
d. Overhang depths is calculated for the window height of 1.82 meter.
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e. Effect of the overhang surfaces, internal and external, on solar radiation and
natural light distribution are negligible.
f. Bare window without overhang is considered as the base-case model.
Table 4.1 presents the overhang configuration to be tested and the respective
overhang ratio (OHR) or projection factors (PF), in the study.
Table 4.1:
Description of overhang depths of the experiment
Overhang Ratio
Overhang Depth
OHR = D/ Hfen
In Meters
In Feet
0 (Base Case)
0.4
0.6
0.8
1
1.4
1.6
0
0.73
1.09
1.46
1.82
2.55
2.92
0
2.4
3.6
4.8
6
8.4
9.6
6.0 m (20 ft)
0.9 m
(3 ft)
External Horizontal Shading device
1.82 m
(6 ft)
0.9 m
(3 ft)
External Wall
6.0 m (20 ft)
2.8 m
(9 ft)
4.4 m (14 ft)
Internal Wall
External Window
Figure 4.2:
Office room with overhang design
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4.2.4 Office Room Characteristics
Characteristics of the building materials, external surface colours and
component sizes are determined based on previous studies by Kannan (1991). The
building specifications for the simulation are as follows:
1) The building’s external wall construction is 200mm thick medium weight
concrete blocks with 50mm cement plaster. The total U value is about 0.5
W/m2 K, which is a similar to the value of common brick wall with insulation
(Kannan, 1991).
2) The total U value for the internal walls is about 2.8 W/m2K. Inside visible
reflectance from the wall surface is 0.5. The ceiling and the floor U values
are about 2.0 W/m2K and 0.5 W/m2K respectively. Reflectance values for
ceiling and floor are taken as 0.7 and 0.2 respectively.
3) Single clear glazing with 3mm thickness was used for the window. The
properties of the existing glazing are as follows: 0.89 visible transmittance,
0.83 solar transmittance, 1.0 shading coefficient and U value is 0.5 W/m2K.
The base office room and the modified office room configurations with
different external horizontal overhang depths will be used to investigate the
objectives of the study. Further, the characteristics of the models will be determined
based on the types of variables to be investigated and the study procedure.
4.3 Methods of Energy Evaluation
Different interrelated issues influence the energy consumption in buildings.
Awareness in energy issues and energy management are important measures that can
play a significant role in the building design process. According to Al-Homoud
(2001), energy analysis in buildings is important to achieve the following:
138
o To determine the alternative energy efficient design options, systems, subsystems and equipments
o To allocate an annual energy budget
o Compliance with energy standards
o Economic optimization
The procedures for estimating energy requirements vary considerably based
on the complexity of the analysis. In general they can be categorized as simplified
energy calculation methods and detailed energy calculations methods.
4.3.1 Simplified Energy Calculation Methods
The most commonly used simplified energy estimating methods are degreeday method (DDM), modified degree-day methods (MDD), variable based degreeday methods, bin-method and modified bin methods (ASHRAE, 1989).
The degree-day and modified degree-day were single measure steady state
methods that can be used only for heating calculation in small buildings. The results
were based on the average conditions and out door weather variation were not
accounted. Also, these methods cannot be used for cooling load calculations
therefore not applicable for building energy calculation under the tropical climate
conditions. The variable based degree-day method uses the same concept of DDM,
but counts the degree-day based on the balance point temperature for the building.
According to the ASHRAE (1989), the balance point is the average out door
temperature at which the building requires neither heating nor cooling. The variable
based degree-day method considers all factors that influence the balance
temperatures, such as indoor temperatures, thermal properties of building elements,
heat gain from appliances and solar radiations. Although this method can be used for
both heating and cooling load calculation, generally the cooling load calculation are
difficult compared to heating load calculations (Al- Homoud, 2001). This is mainly
139
due to the complexity of heat gains in buildings, infiltration and the effects of
humidity.
The bin-method and the modified bin-methods consist of performing
instantaneous heating and cooling energy calculations at many different outdoor dry
bulb temperature conditions. This method involves making instantaneous energy
calculations at several different outdoor temperatures. The bin method only uses
peak loads to establish a load profile. It accounts on hourly weather data rather than
daily averages. The modified-bin method allows off-design conditions which
calculate diversified load values rather than peak loads. The diversified load profile
is characterized by average solar gains, average internal loads profile, secondary
systems and plant equipment effects. Some of the constraints in using the bin
methods are: not reliable for buildings with complex high solar radiation effects and
with high thermal mass loads and also the building size is limited between 5002500m2 (Al- Homoud, 2001).
4.3.2 Detailed Energy Calculation Methods
Assessing building energy performance is a complex process. Each system is
(building design and envelope, mechanical system and management system) interrelated and each set constraints on one or more of the others. Furthermore, each
system may consist of several subsystems, for example the building design and
envelope designs relate in minimizing heat gains, maximize daylight utilization,
achieving high thermal comfort satisfaction, controlling air movement. The unsteady
climatic excitation is another major parameter affecting the building energy
performance. Therefore, building energy performance is inherently a dynamic as
well as a complex process in which many parameters change over time and at
different rates (Clarke, 1993; Hong et al, 2000; Bouchlaghem, 2000).
These complex processes of the real system is abstracted and implemented in
a detailed simulation model with reasonable assumptions. Simulation models are
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flexible performance tools used to produce a set of selected measures that reflect the
performance of the simulated system (Al- Homoud, 2001). A series of mathematical
models are developed for building and its energy system representing the following:
a. Thermal behavior of the building structure
b. Thermodynamic behavior of the air-conditioning delivery system
c. Mathematical relationship between loads and energy requirements of
primary equipments
d. Relationship between the daylight and artificial lighting energy
requirements
These models are logically linked with each other to obtain an overall energy
performance of the correspondence system or in the building design. Al- Homoud,
(2001) points out that there are two modeling strategies being used in evaluating the
building energy performance. They are the sequential approach and simultaneous
solution approach. In the sequential approach, the loads are calculated in step by
step in following order. First the space loads, then the secondary system loads
followed by the primary system loads and finally the energy cost (figure 4.3). The
output of each step is used to execute the next step. According to Al- Homoud,
(2001) this approach lacks interaction between the loads, system and plants which
may produce questionable results. For instance, when the equipment capacities
cannot meet the required load, this will effect on the ultimate result.
Hourly
system
Loads
Peak Loads
Weather
Data
Space
Load
Analysis
Building
Characteristics
& Operating
profile
Secondary
System
Analysis
System
Characteristics
& Operating
profile
Energy Use
Primary
System
(Plant)
Analysis
Economic
Analysis
Life Cycle
Costing
Economic
Data
Equipment
Characteristics
Figure 4.3: Sequential simulation approach. Source: Al- Homoud (2001)
141
In the simultaneous approach, the loads, systems and plant models are solved
simultaneously at each time step as shown in figure 4.4 (Al- Homoud, 2001). This
provides more accurate results compared to sequential approach, but the simulation
process is a complex mechanism.
Hourly
system
Loads
Peak Loads
Weather
Data
Space
Load
Analysis
Building
Characteristics
& Operating
profile
Secondary
System
Analysis
System
Characteristics
& Operating
profile
Energy Use
Primary
System
(Plant)
Analysis
Economic
Analysis
Life Cycle
Costing
Economic
Data
Equipment
Characteristics
Figure 4.4: Simultaneous simulation approach. Source: Al- Homoud (2001)
Due to the complexity, detailed energy evaluation methods are incorporated
in computer programs to conduct the calculations. This enables to effectively
analyze the building energy performances with accuracy and faster. However, single
measure simplified calculation methods can be carried out by hand.
4.4 Methods of Studying Energy in Buildings
A literature survey of previous work suggested that solar shading has a direct
impact on building cooling load, heating load, electric lighting load and daylight
distribution. Various experiments have been carried out to analyze and evaluate the
impact of solar shading on above aspects separately. Previous works suggested three
types of experimental methods commonly used in energy related research on shading
devices. They are actual building measurements, simulation studies and use of
simple calculation methods. A detail description of methods used in recent research
on energy evaluation is given in Appendix A. Choosing the appropriate method to
142
meet the objective of the studies and the expected outcome of the research will save a
great deal of time and effort (Hamdan, 1996).
Intended primary objective of the present study is to determine the cooling
and lighting energy balance due to daylight utilization as a function of external solar
shading device. To consider the correlation between above parameters in the design
of shading devices is to study their impact on building energy use (Reinhart, 2001;
Dubois, 2000; Shaviv, 1999; Lee, 1998).
4.4.1 Manual Calculation Methods
Traditionally manual calculations using pre-selected design conditions and
‘rule of thumb’ were applied throughout the design process (Hong et al, 2000). Most
manual calculations are based on steady state conditions, where factors influencing
the heat transfer are considered under constant state. Therefore, manual calculation
approaches frequently led to oversized plant and system capacities and poor energy
performances. Also, it is based on average conditions and does not account for dayto-day weather variations. Another constrain in manual calculations is the difficulty
to evaluate the effects of natural lighting and artificial light integration.
4.4.2 Field Study or Full Scale Method
The main constraints to carry out experiment in real building or using scale
model are complex and comprehensive procedure in methodology, limitation in
available equipment, limited budget, time consuming and limited man power.
Moreover, to obtain approval to use the building and to obtain information takes
longer time and persuasion due to the attitude of the building owner, architect and the
builder (Hamdan, 1996). Also at present there is no building built for low energy
performance except for the Multimedia Low Energy Office (MEWC-LEO) building
in Putrajaya. It is the first building which integrates comprehensive features of
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energy efficient features, built in Malaysia. The building was under construction
during the present study. Hence, the performance of the MEWC-LEO building is
still under investigation and thus the results are still limited during the present study
was conducted.
Well equipped research laboratory or full scale mockup experimental rooms
for energy experiments are not yet available in any architectural school or in any
other research institutes in Malaysia. However, combined experiments were carried
out to overcome the shortcoming from any particular methods stated above and to
verify the findings (Dubois, 2001; Abdullah-Abdulmohsen, 1995; Chavez, 1989).
Since each method uses different techniques and uses various equipments, the
combined research methods are costly, time consuming and only appropriate in well
resourced programs (Hamdan, 1996).
4.4.3 Computer Simulation
Due to above stated complex process of building energy performances,
limitations and constraints, the only alternative method that is possible to explore is
to depend on computer simulations. The advantage of using a dynamic energy
simulation is that complex daylight, thermal and radiative processes between the
building, shading device and the out door environment are considered in the
calculations. Thereby any design short comings can be reviewed before finalizing
the design.
Another advantage is that the detailed energy simulation programs can
provide hour-by-hour extensive out-put data. However, they require some time in
learning how to use them, preparing the input, running them and interpreting the
results to the requirement of the research. The accuracy of the programs depends on
the accuracy of modeling building components and on the program input
assumptions.
144
The MEWC-LEO building also optimized the effects of applying the main
energy saving features using the Energy-10 computer software before they were
implemented in the actual design and construction (Kristensen, 2003). This indicates
that optimizing the energy saving features and calculating the energy balance of the
building using computer simulation is an acceptable method in designing energy
efficient buildings.
4.5 Selection of Computer Program
Energy simulation in buildings offer a valuable tool for architects and
engineers to evaluate building energy consumption before the building is built. In
recognition of the significance of energy use in buildings, large and complex energy
simulation programs have evolved. At the core of all simulation models is a
mathematical representation of the thermal and optical transfer processes occurring
within the building and plant systems (Clarke, 1993).
Though there are more than one simulation programs that meet the
requirement for any given problem, there is no single program that can perform all
kind of simulation (Hong et al, 2000; Hamdan, 1996). According to Hong et al
(2000) there are three important factors to consider in selecting an appropriate
simulation program:
a. Purpose of the study: Understanding the nature of the problem expected to
solve with the use of the simulation program.
b. In terms of cost: Includes software cost, cost of the computer platform, user
training cost should be within the study budget and period.
c. Available facilities: Selected program should be able to run on existing
computer facilities, especially in personal computer (PC).
Balcomb (1998) describes that the following factors should be part of the
simulation program to make the program easy and faster to use:
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a. The building should be described graphically using CAD tools or user
friendly
interfaces.
b. Automatically modifying the design description to effect the application of
energy efficient strategies.
c. Estimating the size of the HVAC equipment requirement to meet design day
loads.
d. Option of evaluating various parametric schemes.
e. Displaying results in an understandable way either graphically or in spread
sheets (tabulated).
4.5.1 Requirement of the Study
The purpose of the study is to understand the interaction between the solar
shading, solar heat gain, daylight and energy needs of high-rise office building.
Therefore, any simulation program chosen should be able to analyze effect of
building design features on solar radiation, daylight, cooling load, lighting load and
calculate saving due to daylight utilization. Thus, the software must have following
criteria:
a. Provide required climate condition and weather data for specified location of
the study being carried out; e.g. Kuala Lumpur, Malaysia; tropical climate;
latitude: 3.120, longitude: +101.600; time-zone: +7
b. Estimate the incident solar radiation, heat transmission and resultant daylight
levels.
c. Provide daylight/ electric light control strategies and estimate the electric
lighting trade off due to daylight utilization.
d. Provision for parametric evaluation, e.g. options in creating different
geometry of external solar shading devices
e. Provision and easy construction of the required building configuration,
operating schedules, HVAC system and plant sizing etc.
f. Simulate hourly values of required parameters and annual energy calculations
to evaluate the trade off between cooling load, lighting load and the total
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energy consumptions due to daylight utilization as an effect of external solar
shading system.
4.5.2 Review of Energy Simulation Programs
Kristensen (2003), Marsh (2002), Hittle (2001), Crawley (2001), Hong
(2000), Balcomb (1998), James J. Hirsch (2000), Pasqualetto (1997) and McHugh
(1995) have investigated some available commercial energy simulation software.
However, the following simulation programs enable to fulfill the required criteria of
research and was further reviewed; Building Loads Analysis and System
Thermodynamics (BLAST), BSim 2002, ECOTECT, Energy-10, Ener-Win, Energy
Plus, IES Virtual Environment, Power DOE and eQUEST-3 DOE 2.2 (See Appendix
D for detail summary of the review).
According to the review, the Radiance-IES module in the IES Virtual
Environment (IES VE) simulation program creates a better daylight modeling
capabilities with photo-realistic pictures and contour of illuminance than other
programs discussed. The Energy-10 and DOE 2.2 includes the daylight calculations
simply to estimate the savings due to dimming and capture the thermal effects of the
natural lighting for energy calculations. It is important to understand that Energy-10
or DOE 2.2 is not daylight design tools but structured for complex energy
calculations. The DOE 2.2 calculation engine incorporates the daylight results
directly into the control schedule for lighting, thus models cooling loads reduction or
gains and demand savings in lighting, cooling and total energy consumption. The
DOE 2.2 program also provides a larger range of simulation variables. Apart from
above capabilities, the required criteria of the research and considering the financial
constraints, the eQUEST-3 user interface of the DOE 2.2 is chosen in order to
analyze the impact of solar shading integrated with daylight on the building energy
performance.
147
4.6 The eQUEST-3 Computer Simulation Program
The simulation “engine” within eQUEST-3 is derived from the latest official
version of the DOE-2.2. However, eQUEST-3’s engine DOE-2.2 extends and
expands the previous version of DOE-2 capabilities in several ways. This include
HVAC plant operations, interactive operation between daylight and thermal loads,
dynamic default calculations and selection of energy conserving or peak demand
reduction alternatives.
The eQUEST-3 energy simulation program is in the process of being
submitted for certification as Title-24 (California's Energy Efficiency Standards for
Residential and Nonresidential Buildings) compliance software (Shank and
Lunneberg, 2003). Shank and Lunneberg, (2003) and Brown et al (2003) reported
that this software is proven reliable and validated for evaluation of energy efficiency
measures of typical building forms.
The DOE-2 program for building energy use analysis provides the building
construction and research communities with an up-to-date, unbiased, welldocumented computer program for building energy analysis. The DOE-2 is a
portable FORTRAN program that can be used on a large variety of computers,
including PC's. Developments and updates of the DOE-2 program have continued
since the first version. Each new version of the program is denoted by appending
numbers and letters for major and minor changes, respectively (Al-Homoud, 2001).
Since its first release in late 1970’s the DOE-2 has been widely reviewed and
validated in the public domain{Meldem, R. & Winkelmann,1998; Holz et.al, 1996
(DOE-2); Kannan, 1991(DOE 2.1C); Reilly et al,1995; Pasqualetto et al., 1998; Lam
& Li, 1998 and Carriere et al., 1999 (DOE2.1E)}. Based on the DOE-2 engine there
are several interfaces developed by the resellers. The main difference between each
interface depend on their licensee and simulation cost. The freely available programs
only provide access to selected modeling capabilities.
148
4.6.1 Simulation Procedure
This section will outline the sequence of the simulation approach, from
acquiring the required data and the construction of the model to the output of the
results. Figure 4.5 illustrates the flowchart of the DOE-2.2 simulation engine used in
the eQUEST-3 program. According to the program description, the DOE-2.2 has one
subprogram for translation of input data (BDL processor) and three simulation
subprograms (Loads, HVAC, and Economics).
Standard Library
User Input
BDL Processor
User Library
Building
Description
Simulation
Weather
Data
Loads
Output
Report
HVAC
Economic
Figure 4.5: DOE 2.2 Simulation engine structure.
Source: DOE 2.2 Building Energy Use and Cost Analysis Program. Vol.1: Basics
The loads simulation subprogram calculates the sensible and latent
components of the hourly cooling or heating loads for the each user design spaces in
the building. The loads program sums the loads from each type of heat gain into a
total load, which it passes to the HVAC program (figure 4.6). The building
cooling/heating load is responsive to weather and solar conditions, lighting and
equipment, schedule of people, infiltration, heat transfers from building envelope
elements and to the effects of buildings shades on solar radiation. Daylight
calculation of the program is incorporated with the specific lighting load
calculations. The calculations were performed by applying a room weighting factor
149
to the heat gains to determine the loads. The overall simulation procedure is
performed in four steps. The detail explanations of the steps are as follows:
Heat
Gains
Weighting
Factor
Conduction
gain
Solar
gain
Lights
gain
People
gain
Equipment
gain
Source
gain
Infiltration
gain
Conduction
WFs
Solar
WFs
Lighting
WFs
People
WFs
Equipment
WFs
Sources
WFs
Infiltration
WFs
Loads
Conduction
Load
Solar
Load
Lighting
Load
People
Load
Equipment
Load
Source
Load
Infiltration
Load
HVAC
program
Total
Loads
Thermal equation
Air Temperature
WF
Figure 4.6: Calculation procedure of loads from heat gains.
Source: DOE 2.2 Building Energy Use and Cost Analysis Program. Vol. 3: Topics
4.6.1.1 Step I: Data Requirement
Initial step involves preparation and gathering the required data to develop
the simulation model. The approach has to focus on the design questions intended to
solve using the simulation model. The data required for the simulation (with
possible assumptions) were obtained based on the literature review discussed in
chapter three (3).
4.6.1.2 Step II: Preparation of the Models
The required building model can be created using eQUEST-3’s building
wizard (figure 4.7). This wizard allows all the data gathered prior to the simulation
under specified dialog boxes to be incorporated. The models were generated for six
horizontal overhang options on the east and west orientations, five horizontal
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overhang options for the north and south and for two natural-light design criteria
(table 4.2). The following details are required by the wizard to generate the specific
models for simulation:
a)
General information
This section includes building type, weather file coverage, overall size of the
building, utility rates, cooling equipment and option of daylight utilization.
Depending on the building type, set defaults for the HVAC system, construction
materials, operation schedules and loads will be selected by the program. These
default values are derived from the up to date simulation program library. These
values are based on the ASHRAE supported research projects. However, these
values are tested and validated for temperate climate conditions, e.g. HVAC system
details, construction materials and operation schedules. In such cases the program
allows for user input values and set up the simulation conditions to represent the
corresponding simulation conditions.
Figure 4.7
Typical eQUEST-3 building wizard screen
The weather file coverage, region and city option enables the user to specify
the required climatic weather file for a specific location. The program allows three
choices of climatic data; 16 California climate zones, several other cities in United
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States and from the standard DOE-2 weather files which includes weather data for
Kuala Lumpur. Having the option of selecting required climatic data and the HVAC
system detail (cooling/heating) as well as the option of daylight utilization, enables
the program to be used in any climatic condition for load calculations. In the tropics,
the cooling and daylight components are more important than heating.
Table 4.2:
variables
Summary of shading strategy with design variables and performance
Design Variable
Orientation
East
External overhang
Projection Factor
(Depth in meters)
0 (0)
Base case
0.4(0.73m)
West
0.6(1.09m)
North
0.8(1.46m)
South
1.0(1.82m)
1.4(2.55m)
Daylight
Design Criteria
With Naturallight Utilization
Without
Natural-light
utilization
Performance
Variables
* Incident Solar
Radiation
* Solar Heat
Gain
* Work Plane
Illuminance
* Cooling Load
* Electricity
Consumption
1.6(2.92m)
b)
Building Description
The building description section allows establishing the building foot print,
building orientation, building construction and door-window detail options. Shape
and size of the building model is created using the data input of building foot print
dimensions. However, the program allows creating custom made building shapes
using a Cartesian co-ordinate’s screen. Default values are given for exterior and
interior surface constructions (roof, wall ceiling finishes and colour) based on the
building type. The program also allows adiabatic wall surfaces to be created if
necessary. The detail section provides flexibility to incorporate user define values if
necessary.
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The doors and windows are selected according to the orientations of the wall
surface. For each orientation, required number of door and window elements can be
selected based on the length and height of the wall. A percentage value can be
suggested for the window as compared to external wall surface or internal wall
surface (within floor-to-ceiling of the wall with the window). Two options of
windows are generated; identical windows divided within the wall space and a single
window to cover the entire window area specified. Materials and glass types are
selected from the default library or user can create his/her own library of materials.
This screen also includes external shading device dimension for relevant
windows. Only two types of external shading devices are included in the program;
horizontal overhangs and vertical fins (figure 4.8). Additional requirements if
necessary such as changing length, width and angle of correspondence devices can
be adjusted in the detail section.
Figure 4.8: The eQUEST-3 exterior window shades and blinds wizard screen
c)
Daylight Utilization
The daylight input screen is displayed if only the daylight option in general
information screen was selected (figure 4.9). Two daylight concepts are allowed in
the daylight modeling; sky light and side light options. For multistory buildings,
three daylight zones were allowed, ground floor, typical middle floor (all middle
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floor zones were summarized into one typical floor) and top floor zone. In non
daylight utilization option, internal illuminance is provided by artificial means.
Hence, the building will be converted into a daylight-rejecting building type.
Figure 4.9:
d)
The eQUEST-3 daylight zoning wizard screen
Activity Area and Occupied Internal Loads
Heat gains from internal loads (people, lighting, equipment) contribute
significantly both from their direct power requirement and indirect effect on
cooling/heating requirement. Internal loads are specified based on user input for
activity area. The program load schedules are based on two levels of activities,
during occupied and unoccupied hours. According to the type of building being
analyzed, the activity areas are allocated by percentage value. Preferred occupancy
density and out side ventilation rate (per person) were also included to the program.
Then the program allocates these loads to each HVAC zone for calculations.
e)
Building Operations and Schedules
The program permits up to two building usage schedules, a main schedule
and an alternate schedule. The alternate schedule is to be used if there is different
schedule for a second season. Apart from two schedules, it also gives the option of
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three day types; five week days, two weekend days and a holiday. This enables to
specify usage of building for three different activity patterns, if required.
f)
System and Plant Information
Zone cooling, heating and ventilation loads are transferred to the HVAC
module to model the performance of the loads. The transfers of energy to these
systems are dynamic in nature and the loads are calculated in hourly basis.
Undersized equipment may affect the zone temperature and thereby affect the load
calculations (Hittle, 2001). Therefore, proper control modeling is an essential part
for arriving at better simulation and correct system loads. However, default system
types are based on the building type and the coil types selected under general
information screen (figure 4.10).
Figure 4.10:
The eQUEST-3 HVAC system wizard screen
Primary equipments such as chillers, cooling towers and boilers also
influence the energy consumption of the building. General understandings of their
functions are required. Selecting a plant type and the capacity is based on survey
done on buildings and chosen from most commonly used system.
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4.6.1.3 Step III: Detailed Interface-Selecting Simulation Parameters and
Perform Simulation
The detail interface option allows you to further refine and edit the input data
to suit the requirement of the study. The energy efficiency measures (EEM) wizard
in detail inter face allows to select ten design alternatives to the base building
description. However, alteration to the building made in the detail interface will not
be communicated back to the ‘building wizard’. Therefore, the EEM wizard can be
used only for buildings described by the ‘building wizard’. The detail interface also
allows monitoring the building in three-dimensional form.
Modifications in detail interface allows for alterations in two methods: using
“spreadsheets” and “detail tabbed dialogue box” (figure 4.11). These spreadsheets
and dialogue boxes can be used to review, input or modify general features related to
the respective components. Buildings with alterations and modification in detail
interface enables design alternatives to be analyzed and simulated for energy
consumption to the base case model only.
Within detail interface, user is permitted to select simulation parameters up to
60 variables from the following tables; global weather data, building loads, space
loads, external wall loads, window loads, zone loads, system loads, and plant loads
(figure 4.12). Based on the selected variables the hourly reports were calculated for
every hour of the day, daily summary, monthly summary and yearly summary for the
correspondence year. These reports can be used for detail analysis of the expected
out come or results of the simulation.
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(i) Component tree
Figure 4.11:
Figure 4.12:
(ii) Window properties screen
The eQUEST-3 detail interface screen
The eQUEST-3 hourly results selection screen
Once the descriptions of the preferred building are completed, the simulation
can be performed by pressing the run simulation button. The simulation is
performed for the designated annual year. Overall numbers of simulations permitted
to be performed were 52.
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4.6.1.4 Step IV: Review Simulation Results
The program provides a graphical simulation output in two forms; single run
report and comparison report. These results only present monthly and annual energy
consumption by endues, utility bills and peak demands (figure 4.13). The hourly
values are written in text form; therefore the required data need to be transferred to
excel work sheets to obtain graphical descriptions.
Figure 4.13:
The eQUEST-3 results screen of annual end use energy consumption
Overhang
Hypothesis:
Seven Options
Orientation:
East, West, North
& South
Daylight design
criteria:
With daylight &
non daylight
utilization
Figure 4.14:
Step I
Data Requirement
Step II
Preparation of the Models
Step III
Detailed Interface-Selecting
Simulation Parameters and
Perform simulation
Step IV
Review Simulation
Results
The eQUEST-3 simulation procedures
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4.6.2 Simulation Limitations
The performance of the simulation program is bound to have few limitations
as discussed bellow:
1) Weather files with measured solar radiation data need to be used for
accurate daylight simulation results. Use of non-solar weather files will not
produce accurate daylight results.
2) The program considers three sources of incident solar radiation on the
windows and walls; directly from the sun, directly from the sky and reflected
from the ground. Reflection from other external surfaces, like neighboring
buildings is not considered in the calculations. Also, external shading
surfaces only block but do not reflect solar radiation. Solar radiation
calculations are based on global horizontal and beam radiation. Radiations
falling on vertical surfaces were calculated based on above radiation data.
3) The built in daylight illuminance calculation works best when most of the
illuminance reaches the reference point directly from the window without
reflection from room surfaces. Following are the limitations in daylight
calculations:
o
Program cannot simulate interior or exterior light shelves, light scoops,
skylight with deep wells and rooms with internal obstructions (partitions
etc.) that block light from window.
o
The computer model allows maximum of two reference points to predict
the illuminance and luminance values of daylight penetration at a single
run of the simulation.
o
Reference points located at a distance more than three times floor-toceiling height for a side lit room will create error in daylight
calculations. Also, a reference point too near to the window will over
predict the lighting savings.
159
o
Light reaching the reference point from another window of an adjacent
space is not calculated in the simulation.
o
The sunlight illuminance ratio (SIR) and the daylight factor (DF) are
calculated for standard clear and overcast sky conditions for a series of
20 different solar altitude and azimuth values covering the annual range
of solar position. However, the overcast sky condition is considered
only for one sun position (solar altitude 10 and azimuth angle 290)
therefore it can be assumed that the daylight calculations are performed
for clear sky conditions. The hourly internal illuminance at reference
points were obtained as total illuminance sum of:
o
direct sunlight
o
light from sky and ground
Since, daylight factor and sun illuminance ratio are relative measures
and are not absolute measures of illuminance, the internal illuminance is
referred as work plane illuminance, which is given in lux values. Also, the
total illuminance is a combination of direct sunlight and daylight, the term
natural-light is being used instead of daylight when such clarification is
required.
4) The main limitation of the program is that the selected foot print shape
applies to all floors of the building. Hence, there cannot be two different
floor arrangements for the specified building.
5) Attached shades are limited to overhangs and vertical fins only.
Horizontal fins and egg-crate shading devices are not included in the
program. For daylight calculations, attached shades are treated as “opaque”
and “black”, hence they neither transmit nor reflect incident light. A
horizontal over hang models the natural-light by blocking direct and diffuse
light from sun and sky respectively and does not consider any reflected
lighting from the ground.
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Simulation design conditions of typical office room were discussed in the
following section, complying with the above limitations.
4.6.3 Simulation Design Conditions
This section discusses the preparation of the basic conditions of different
variables for the simulation. The design conditions to conduct the simulation were
adjusted based on literature review (Azni Zain-Ahmed, 2002; MS 1525:2001;
Dubois, 2000 & 2001; Bülow-Hübe, 2001; Lee et al, 1998; Harrison et al, 1998;
Abdullah-Abdulmohsen, 1995; Kannan, 1991; ASHRAE, 1989 and Robbins, 1986).
Required assumptions were made to accommodate the limitations of the computer
program as discussed in previous section (4.6.2).
4.6.3.1 Office Room Characteristics
The geometry of the base model office room and the tested overhang models
were developed using the building wizard. The descriptions of the models are
according to the details discussed in section 4.2. In order to minimize the heat
transfer from the interior surfaces such as internal walls, ceiling and floor were
constructed as adiabatic wall surfaces. Adiabatic walls can have reflective and
absorptive properties, as well as the ability to store heat. They do not, however,
allow heat to be transferred between spaces. This gives the option of minimizing the
impact of heat transfer of the adjacent spaces.
4.6.3.2 Indoor Design Conditions
a) The desired design lighting level is an important input data. The program
presumes this lighting level to calculate the supplemented artificial lighting to
achieve the required illuminance level when natural light is inadequate. In
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this study the internal illuminance is described as the “work plane
illuminance”, and the target illuminance level was considered as 500lux.
b) As discussed in section 4.6.2 the daylight photo sensors were limited to
two and their locations were determined by two input data; height above floor
and percentage depth of the zone from external vertical window wall. The
height is selected as work plane height of 0.9 meter. The location for
reference points were selected as 50% and 90% of the zone depth. Thus
reference points were positioned at 3.0 meter and at 5.7 meter from the
window pane (figure 4.15). The two positions were selected to represent the
mid zone value and back edge value of the considered room. Also, the sensor
points were aligned in the center of the length of the window pane.
6.0m
3.0m
Ref pt 01
3.0m
Ref pt 02
5.7m
3.0m
Plan
D
H
Work plane height
2.8m
Ref pt 01 Ref pt 02
0.9m
Section
Figure 4.15:
Daylight photo sensor positions in office room model
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c) Decrease in natural-light level will be supplemented with artificial lighting
to maintain the required illuminance level in the space. Vis-à-vis when
adequate natural-light is available, the artificial lights should be switched off.
The continuous/off light control strategy was adopted in this study as it gives
the best energy efficient control option (Chavez, 1989; Robbins, 1986).
d) The indoor design temperature is set to 240C (75.2 0F). The value was
determined based on the Malaysian Standard (MS 1525:2001).
4.6.3.3 Internal Load
a) The maximum light power requirement is determined as recommended by
The Malaysian Standard (MS 1525:2001), which is 20 W/m2 (1.8 W/ft2) for
office buildings.
b) The equipment load installed capacity is, 14 W/m2 (1.3 W/ft2). This value
is based on commonly used office buildings equipment loads.
c) The modeled office room is assumed to be used by a single person, thus,
minimize the occupants load in energy calculations.
Heat gains from internal loads (people, lighting, equipment) contribute
significantly both from their direct power requirement and the indirect effect on
cooling/heating requirement. Internal loads were specified based on user input
(discussed above) for activity area, which were allocated as a percentage value.
Preferred occupancy density and out side ventilation rate (15 CFM/person) were
specified to the program. Then the program allocates these loads to each HVAC
zone for calculations.
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4.6.3.4 Operating Schedules
Schedules of operations indicate how the building is being used. The
information includes; when the building occupancy begins and ends (time, days of
the week and seasonal variations), occupied indoor thermostat set points and internal
equipment operational schedules. Most office buildings have similar pattern of use
where they are typically occupied during regular day time working hours, from 9:00
am to 17:00 pm. Working days are considered to be from Monday to Friday and
weekends were assumed as holidays. During the night and weekends it is considered
as unoccupied or partially occupied. Based on above assumption the default values
of operating schedules for the HVAC and internal equipment operation schedules are
used in the program.
4.6.3.5 Outdoor Design Conditions
a) Weather data is a primary requirement for any energy simulation program
or any energy calculation method. Building thermal loads depends on the
variation of outdoor weather conditions. Accuracy of any simulation
program depends on incorporating this dynamic nature of external weather
conditions for energy calculations. These data consists mainly of the
following hourly data; the dry and wet bulb temperatures, humidity ratio,
atmospheric pressure, wind speed and direction, solar radiation, cloud cover
and sky condition data of a specific location. Depending on the available
weather data, (hourly or monthly average values) the program is developed to
generate their own binary files to be used during the simulation
The DOE-2 weather processor accepts following weather data types:
TRY, TMY2 and WYEC2. The weather variables used by the program are
the variables measured at weather stations. When information is missing for
one or more hours, data is filled in by linear interpolation from previous
available value to next available value. Hourly solar values are obtained from
measured weather tapes for specific location. In the case of files without
164
solar data, the program calculates solar values using the ASHRAE clear sky
model, clearness number, cloud amount and cloud type from the program
weather file. The solar weather file contains; total horizontal solar radiation
and direct normal solar radiation (DOE-2 engineering manuals, 1982). As
discussed in Chapter 2, it is assumed that use of required weather data for
Kuala Lumpur; Latitude: 3.120, Longitude: +101.60 and Time zone: +7 from
the DOE-2 weather, Asian-sp files for international locations, will provide
accurate results in the simulation intended.
b) Site data includes information of the specific location, such as the ground
temperature (330C), atmospheric moisture (1.3 inches of water in the
atmosphere recommended for humid climates), atmospheric turbidity (0.12,
the amount of particle in the atmosphere recommended for urban setting) and
weather station height is taken as 16.0 meter from sea level. However, the
site terrain for the office room is considered as exposed, thereby to minimize
the effects of adjacent buildings on internal lighting and thermal loads.
c) The fenestration of the office space is tested for the north, east, south and
west orientations. Although north and south orientations are recommended
for low energy consumptions for buildings located closer to the equator, there
is no clear conclusion made on energy saving when solar shading were
applied. Therefore, the impacts of the main cardinal orientations on energy
consumptions were considered for the above selected overhang depths.
This section discussed the selected eQUEST-3 dynamic energy simulation
program, construction of the base model, characteristics of the base model, tested
overhang ratios, simulation limitations and the simulation design conditions. Table
4.3 illustrates the primary independent variables, dependent variables and the details
set for constant in this study.
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Table 4.3: Variables and constants of the study
Independent
Variables
1. External overhang
depth
2. Fenestration
orientation
Dependent Variables
1. Incident direct solar
radiation
2. Incident diffused solar
radiation
3. Solar heat gain
4. Work plane
illuminance
5. Building cooling loads
6. Building energy
consumptions
Constants
1. Office room geometry
2. Office room characteristics:
• Fenestration glazing size
• Internal and external
surface characteristics
3. Internal design conditions:
• Thermostat set point
• Equipment loads
• Lighting loads
4. HVAC system and plants
5. Activity area
6. Operational schedules
4.7 Simulation Analysis Criteria
The analysis of the study is based on the output data obtained from the
simulation for the tested overhang options. The output results were obtained in two
forms: the hourly values for the designated year and the annual energy consumption
by end use. The hourly results were obtained for the following performance
variables:
i. Direct incident solar radiation
ii. Diffused incident solar radiation
iii. Total transmitted heat gains
iv. Work plane illuminances at both reference points (Ref.Pt.01 & 02)
The hourly data for 21 March, 22 June, 24 September and 21 December were
chosen at four times within general office working hours (9:00, 12:00, 15:00 and
17:00 hours) for analysis. The selected time was based on different position of the
sun within the working schedule from 9:00 am to 17:00 pm. The results of the
incident direct and diffused solar radiation and transmitted heat gains were combined
into a single graph on respective dates and orientations. Likewise, the work plane
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illuminance and the transmitted heat gains were also illustrated in a single graph on
respective dates and orientations. This is to get a better understanding of the
influence of horizontal over hand on the performance variables. The maximum,
minimum and mean work plane illuminance and transmitted heat gain values are
used to describe general performance of the models tested. The annual energy
consumptions by endues are analyzed for the following performance variables:
i. Building cooling loads
ii. Electricity consumption for cooling
iii. Electricity consumption for lighting
iv. Total electricity consumption
Design variables and criterions for evaluation of data were determined from
the literature review presented in chapter three. The overall assessments of results of
the simulation were analyzed as in table 4.4.
Table 4.4: Data analysis indicators and their interpretation
Data Analysis
Interpretation and Performance
Variables
1 Assess the impact of shading strategies
on incident solar radiation
o
o
Direct solar radiation
Diffuse solar radiation
2 Assess the impact of shading strategies
on transmitted solar heat gain
Assess the impact of shading strategies
3
on target work plane illuminance
4 Assess the relationship between
natural-light penetration and geometry
of the correspondence room.
o
Solar Heat Gain
Assess the impact of shading strategy
on annual building cooling load
Assess the impact of shading strategy
on annual energy consumption for
6
cooling, lighting and on total
consumption
Determine the optimum shading
7
strategy
5
500lux Ideal for paper work
300-400lux Drawing offices
Ratio between room depth (Drm ) and window
height (H) to obtain a mean work plane
illuminance of 500lux at deep end of the room
(room depth is calculated from the edge of the
overhang to opposite wall to the window wall)
o With natural light
o Without natural light
o
o
With natural light
Without natural light
Analyzing results in (1), (2), (3), (5) and (6)
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The suggested energy standard for non-residential buildings is 135 kWh/m2
and it is used as a bench mark in describing the energy consumption of the respective
tested overhang models. The analysis of the each tested overhang models will be
evaluated with the correspondence performance variables values for base-case model
(without overhang). Also, all the performance variables were correlated with
overhang ratio (OHR) of the tested overhang models. This gives the designer more
flexibility in determining a shading strategy than fixed depth of an overhang. Also,
for better understanding of the optimum energy consumption due to the solar heat
gains and natural-light utilization, the incremental energy use (IEU) was correlated
with shading overhang ratio. The incremental energy use (IEU) is the difference
between electricity consumption (EC) for base-case model with the tested overhang
model.
∆IEU = ECwith shade – ECbase-case
(4.1)
The incremental energy use (IEU) is calculated for electricity consumption
for space cooling, area lighting and for the total energy as follows:
IEU for space cooling;
∆IEUCL = EC CL (with shade) – ECCL (base-case)
(4.2)
IEU for area lighting;
∆IEULT = EC LT (with shade) – ECLT
(base-case)
(4.3)
IEU for total energy consumption;
∆IEUTOT = EC TOT (with shade) – ECTOT (base-case)
(4.4)
If the ∆IEU is a positive value, an increase in energy consumption occurs due
to the use of shading strategy. Similarly, if the ∆IEU is a negative value, a decrease
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in energy consumption occurs due to the use of shading strategy. Simple trend
analysis techniques are adapted to determine the proportions of variation between
dependent and the independent variables. The predicted values obtained from the
regression equations are compared with simulated values to determine the
appropriateness of using the predicted values for analysis.
Office Room
Configuration
Computer Model
Construction
BASE CASE
Overhang Shading Types
OHR: 0.4, 0.6, 0.8, 1.0, 1.4
& 1.6
Orientation
East, West, North & South
Simulation
Without Natural Light
Annual Building
Energy
Consumption:
Lighting
Space Cooling
Total
Annual
Building
Cooling
Load
With Natural Light
Incident
Solar
Radiation
Direct
Diffuse
Solar
Heat
Gain
Factor
Work Plane
Illuminance:
500lux
Predicted values from
Regression equation
Optimum Overhang Projection Factors and Optimum Energy Consumption
Analysis
Figure 4.16: Overall simulation procedures with design variables and
performance variables
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4.8 Summary
This chapter has discussed the methodologies employed in this study. The
need for the study and the assumptions made for the selection of the base model were
discussed. The main focus of the study was on the effects of the external shading
strategy on building energy use, hence it was recognized the limitation to optimize
all criteria simultaneously. Therefore, a simple perimeter office room from a basic
square modular was generated, (6.0 meter, width x 6.0 meter, depth x 2.8 meter,
floor-to-ceiling height) which could be plugged into any simplified building form or
shape. This designated high-rise office room model was used for further study.
In section two, energy evaluation methods were analyzed to determine a
suitable methodology to study the impact of horizontal shading strategy on solar
radiation, natural-lighting, and energy consumption. The use of computer simulation
was recommended to evaluate different interrelated issues influencing on the
building design and the energy consumption. The eQUEST-3 (DOE 2.2) dynamic
energy simulation program was chosen as the main tool based on following
capabilities; availability of the program at no cost, capability of daylight/ solar
radiation/ heat gain and correspondence energy calculations, option of required
shading strategies, flexibility and easy to use in terms of data input and output,
accuracy in calculations and validity, rapid run time, reliability and compatibility to
be used in different climate conditions. Further, thorough documentation, extensive
data availability and support the ASHRAE standard 90.1 (1999) and the LEED rating
(Leadership in Energy and Environmental Design) indicates the reliability of the
program to perform energy analysis.
The structure of the simulation program was thoroughly examined, which
included four stages. The main independent variables of the study were different
depths of external horizontal shading devices, orientation of the window façade (east,
west, north and south), external daylight and solar radiation availability. The tested
overhang depths were indicated as a ratio to the window height, which was termed as
overhang ratio (OHR) or projection factor (PF); 0 (base-case model), 0.4, 0.6, 0.8,
1.0, 1.4 and 1.6. Use of overhang ratio gives a proportional relationship between
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window height and the overhang projection. Also, the correlation between overhang
ratio and performance variables (work plane illuminance level, incident solar
radiations, heat gains and building energy use) will give more flexibility to the
designer to determine appropriate shading strategies to achieve energy efficiency in
buildings. Finally, the simulation analysis criterions were setup for the data analysis
in next chapter.
CHAPTER 5
RESULTS, ANALYSIS AND FINDINGS:
SOLAR RADIATION AND WORK PLANE ILLUMINANCE
This chapter evaluates the simulation results obtained for both solar radiation
and work plane illuminance for the tested overhang ratios (or projection factor). The
evaluation on solar radiation is based on the incident and transmitted solar radiation
values from the simulation. The lighting analysis is based on the work plane
illuminance which includes both direct sunlight and daylight. Further, in order to
find the correlation between the illuminance and solar heat gain component, the
natural light and solar heat gain results are presented in the same graph as a function
of overhang ratio. The overhang ratio of the external horizontal overhang device is
established based on the proportional relationship between overhang depth and the
aperture height. Finally, the interpretations of the results on the impact of horizontal
shading device on solar heat gain and internal illuminance level are discussed.
5.1 Incident and Transmitted Solar Radiation
The primary purpose of the external solar shading is to reduce the unwanted
solar radiations penetration into the building through the wall aperture. The direct
and diffuse (including reflected solar radiation) solar radiation incident on window
was obtained for four days (21 March, 22 June, 24 September and 21 December), at
four times within general office working hours (9:00, 12:00, 15:00 and 17:00 hours).
The correspondence transmitted and re-conducted solar heat gains are also presented
for better understanding of the impact of horizontal overhang on solar heat gain
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through the window when solar shading is applied. Both incident radiations [direct
and diffuse (including reflected)] and the transmitted solar heat gain were analyzed
as a function of horizontal overhang ratio, for the four main cardinal orientations
(East, West, North and South). The results are presented in figure 5.1 to 5.16.
5.1.1 East Orientation
The direct solar radiation impinge is maximum between 9:00 in the morning
to 12:00 noon on the aperture facing the east orientation. The intensity of direct solar
radiation incident on the bare window (without overhang) is higher at 9:00 hour than
at 12:00 noon on 21 March, 22 June, and 21 December at east orientation (figure.5.1
to 5.4). The reason can be explained as at 9:00 the sun is at the lower altitude angle
than at 12:00 noon. Therefore the intensity of direct solar radiation on a vertical
surface is high at low altitudes, even though the global solar radiation data reveal
higher value at high solar altitudes. But on 24 September the intensity of direct solar
radiation indicates almost the same value at 9:00 and 12:00 hours. This is because
the global solar radiation on horizontal surface obtains lower amount of radiation
during the morning hours than at 12:00 noon. Further, overhang ratio at 1.4 gives the
maximum shade from direct sun at 9:00 hour on the east aperture on all orientations.
Similarly, at 12:00 noon, an overhang ratio of 0.4 can obstruct direct solar radiation
impinge through the aperture on respective orientations.
The diffuse solar radiation incident on window showed a similar pattern
throughout the day for each hour. This indicates application of solar shading devices
had a lesser impact on reducing the diffuse radiation. However, on 22 June and 24
September, intensity of diffuse solar radiation is higher than the direct solar radiation
incident on window. Also results showed that the maximum diffuse solar intensity is
at 12:00 noon on 21 March, 24 September, and 21 December. This is because the
scattering of the diffuse solar radiation, which strongly influenced by the
atmospheric factors and air mass. At low solar altitudes the radiation passes through
a large depth of atmosphere than at higher solar altitudes. Hence at lower solar
173
altitudes, the scattering effect would be distinct and comparatively smaller amount
will be available than at higher solar altitudes.
2
W/m
450
9:00
12:00
375
15:00
17:00
300
225
150
75
0
0
0.4 0.6 0.8
1
1.4 1.6
Direct solar radiation incident on
window
0
0.4 0.6 0.8
1
1.4 1.6
Diffuse solar radiation incident
on window
0
0.4 0.6 0.8
1
1.4 1.6
Transmitted and reconducted
solar heat gain through window
Overhang ratio
Figure 5.1: Direct, diffuse solar radiation incident on window, and transmitted
and re-conducted solar heat gain (W/m2), as a function of overhang ratio- 21 March,
East orientation
2
W/m
300
9:00
12:00
250
15:00
17:00
200
150
100
50
0
0
0.4 0.6 0.8
1
1.4 1.6
Direct solar radiation incident on
window
0
0.4 0.6 0.8
1
1.4 1.6
Diffuse solar radiation incident
on window
0
0.4 0.6 0.8
1
1.4 1.6
Transmitted and reconducted
solar heat gain through window
Overhang ratio
Figure 5.2: Direct, diffuse solar radiation incident on window, and transmitted
and re-conducted solar heat gain (W/m2), as a function of overhang ratio- 22 June,
East orientation
174
2
W/m
240
9:00
210
12:00
180
15:00
17:00
150
120
90
60
30
0
0
0.4 0.6 0.8
1
1.4 1.6
Direct solar radiation incident on
window
0
0.4 0.6 0.8
1
1.4 1.6
Diffuse solar radiation incident on
window
0
0.4 0.6 0.8
1
1.4 1.6
Transmitted and reconducted
solar heat gain through window
Overhang ratio
Figure 5.3: Direct, diffuse solar radiation incident on window, and transmitted
and re-conducted solar heat gain (W/m2), as a function of overhang ratio- 24
September, East orientation
2
W/m
600
9:00
525
12:00
15:00
450
17:00
375
300
225
150
75
0
0
0.4 0.6 0.8
1
1.4 1.6
Direct solar radiation incident on
window
0
0.4 0.6 0.8
1
1.4 1.6
Diffuse solar radiation incident
on window
0
0.4 0.6 0.8
1
1.4 1.6
Transmitted and reconducted
solar heat gain through window
Overhang ratio
Figure 5.4: Direct, diffuse solar radiation incident on window, and transmitted
and re-conducted solar heat gain (W/m2), as a function of overhang ratio- 21
December, East orientation
The results of the total transmitted and re-conducted (direct and diffuse) solar
heat gain into the space showed that higher heat gains are obtained during the
175
morning hour than at noon (figure 5.1 to 5.4). This is mainly due to the direct solar
radiation penetration. Lower values of solar heat gain were indicated at 15:00 and
17:00 hours which were caused by the diffuse component of solar radiation. The
figures 5.1 to 5.4 exhibited a higher gradient curve with the increase in overhang
ratio for 9:00 and 12:00 hours than at 15:00 and 17:00 hours. This indicates that by
reducing heat gain from direct solar radiation reduced the total heat gain into the
space significantly.
5.1.2 West Orientation
Figures 5.5 to 5.8 illustrate that direct solar radiation incident on the west
oriented bare window is higher on 21 March and 24 September (420 W/m2 & 210
W/m2 respectively), than on 22 June and 21 December, (90 W/m2 & 120 W/m2).
This is mainly due to the position of the sun related to the location of the study.
Hence, during 21 March and 24 September the sun rotates closer to the tropical
region while on 22 June and 21 December the sun rotates furthest from the tropical
region. Also the hourly direct solar radiation is high at 17:00 hour than at 15:00 hour
when the sun is above the equator and at low solar altitudes. Further on 22 June and
21 December, the intensity of the direct solar radiation incident on the west oriented
window is higher at 15:00 than at 17:00 hours.
This implies that when the sun is in equinox the solar altitude angle is an
important aspect in determining the direct solar intensity than the amount of solar
radiation available. In other words, when the sun is at the equinox the distance is
closer to the earth surface, thus the solar intensity is high. However, the direct
radiation incident on the vertical surface (window) depends on the solar altitude and
azimuth angle as to the cosine- law. When the sun is in the solstices the path of
radiation through atmosphere is longer. Thus, lower the solar altitude angle, the
longer the path of solar radiation through the atmosphere. This results in reducing
the amount of radiation reaching the surface due to the momentary state of the
atmosphere.
176
2
W/m
700
9:00
600
12:00
15:00
500
17:00
400
300
200
100
0
0
0.4 0.6 0.8
1
1.4 1.6
Direct solar radiation incident on
window
0
0.4 0.6 0.8
1
1.4 1.6
Diffuse solar radiation incident
on window
0
0.4 0.6 0.8
1
1.4 1.6
Transmitted and reconducted
solar heat gain through window
Overhang ratio
Figure 5.5: Direct, diffuse solar radiation incident on window, and transmitted
and re-conducted solar heat gain (W/m2), as a function of overhang ratio- 21 March,
West orientation
The profile of the direct solar radiation incident on the window when the
solar shadings were applied, exhibited a steep gradient on 21 March and 24
September than in 22 June and 21 December (at 17:00 hour). Hence, when the sun is
over the equator, the horizontal shading devices eliminated the direct component of
solar radiation more effectively compared to the sun is at the solstices. Also at 15:00
hour, overhang ratio of 0.6 and 0.8 are required to block the direct solar radiation on
the equinox days (21 March and 24 September) and solstices days (22 June and 21
December) respectively, from penetrating into the space. Further, overhang ratio of
1.6 achieved a maximum of 50 W/m2 and a minimum of 16 W/m2 compared to 420
W/m2 and 168 W/m2 direct radiation incident on the bare window respectively.
Thus, this reduced the maximum and minimum intensity of the direct solar radiation
incident on window by 88% and 90%, on west oriented window.
The profile of the diffuse solar radiation incident on the window exhibited a
lower gradient. During 21 March and 24 September, diffuse solar radiation incident
on the window is high at 17:00 hour (figure 5.5 and 5.7). Consequently, on 22 June
and 21 December, amount of diffuse radiation incident on the window is high at
15:00 hour, without shading device (figure 5.6 and 5.8).
177
2
W/m
350
9:00
12:00
300
15:00
250
17:00
200
150
100
50
0
0
0.4 0.6 0.8
1
1.4 1.6
0
Direct solar radiation incident on
window
0.4 0.6 0.8
1
1.4 1.6
0
Diffuse solar radiation incident
on window
0.4 0.6 0.8
1
1.4 1.6
Transmitted and reconducted
solar heat gain through window
Overhang ratio
Figure 5.6: Direct, diffuse solar radiation incident on window, and transmitted
and re-conducted solar heat gain (W/m2), as a function of overhang ratio- 22 June,
West orientation
W/m2
450
9:00
400
12:00
350
15:00
300
17:00
250
200
150
100
50
0
0
0.4 0.6 0.8
1
1.4 1.6
Direct solar radiation incident on
window
0
0.4 0.6 0.8
1
1.4 1.6
Diffuse solar radiation incident on
window
0
0.4 0.6 0.8
1
1.4 1.6
Transmitted and reconducted
solar heat gain through window
Overhang ratio
Figure 5.7: Direct, diffuse solar radiation incident on window, and transmitted
and re-conducted solar heat gain (W/m2), as a function of overhang ratio- 24
September, West orientation
178
2
W/m
270
9:00
240
12:00
210
15:00
17:00
180
150
120
90
60
30
0
0
0.4 0.6 0.8
1
1.4 1.6
Direct solar radiation incident on
window
0
0.4 0.6 0.8
1
1.4 1.6
Diffuse solar radiation incident on
window
0
0.4 0.6 0.8
1
1.4 1.6
Transmitted and reconducted
solar heat gain through window
Overhang ratio
Figure 5.8: Direct, diffuse solar radiation incident on window, and transmitted
and re-conducted solar heat gain (W/m2), as a function of overhang ratio- 21
December, West orientation
The values obtained for transmitted and re-conducted solar heat gain on the
west orientation indicated a higher heat gains at 17:00 and 15:00 hours of the day.
The profile of the heat gain into the space indicated a reduction when the overhang
ratio is increased. However, the profile gradient is high at 17:00 and 15:00 hours
than at 9:00 and 12:00 hours, which clearly indicates the impact of the direct solar
radiation on the total heat gain into the space, through the west oriented window.
The maximum and minimum transmitted solar heat gain values obtained on
bare window were 502 W/m2 and 44 W/m2 for east orientation and 620 W/m2 and 52
W/m2 for west orientation. With maximum overhang ratio of 1.6, the maximum and
minimum values of heat gain indicated as 104 W/m2 and 21 W/m2 on the east
orientation and 156 W/m2 and 37 W/m2 on west orientation. These results signify
that the window oriented towards the west gain more heat than the east oriented
window.
179
5.1.3 North Orientation
The direct solar radiation affect on the north façade only on 22 June. During
21 March, 24 September and 21 December, the façade is self shaded from the direct
solar radiation (figure 5.9 to 5.12). This is understandable as the sun is at the north
hemisphere from May to August. Amount of direct solar radiation incident on the
bare window is high during 15:00 hours than at 12:00 hours, where the sun is at a
lower altitude at 15:00 than at 12:00 hour. Also at 9:00 and 17:00 the incident
radiation values are low as the global solar radiation values are low due to the
atmospheric depletion. Further, when the solar altitude angle is lower, the path of
radiation through atmosphere becomes longer. Hence, smaller part of solar radiation
reaches the earth’s surface.
2
W/m
210
9:00
180
12:00
15:00
150
17:00
120
90
60
No direct solar radiation
incident on window
30
0
0
0.4
0.6
0.8
1
1.4
Direct solar radiation incident on
window
0
0.4
0.6
0.8
1
1.4
Diffuse solar radiation incident
on window
0
0.4
0.6
0.8
1
1.4
Transmitted and reconducted
solar heat gain through window
Overhang ratio
Figure 5.9: Direct, diffuse solar radiation incident on window, and transmitted and
re-conducted solar heat gain (W/m2), as a function of overhang ratio- 21 March,
North orientation
At 12:00 noon and 15:00 hour, incoming direct solar radiation on the north
window is blocked by a horizontal overhang ratio of 0.4 (figure 5.10). The profile
also indicates at 9:00 and 17:00 hours, increase in overhang ratio beyond 0.6 does
180
not reduce the incoming direct solar radiation. This means maximum reduction of
incident direct solar radiation can be achieved by overhang ratio of 0.6 on the north
window.
2
W/m
240
9:00
210
12:00
180
15:00
17:00
150
120
90
60
30
0
0
0.4
0.6
0.8
1
1.4
Direct solar radiation incident on
window
0
0.4
0.6
0.8
1
1.4
Diffuse solar radiation incident
on window
0
0.4
0.6
0.8
1
1.4
Transmitted and reconducted
solar heat gain through window
Overhang ratio
Figure 5.10: Direct, diffuse solar radiation incident on window, and transmitted
and re-conducted solar heat gain (W/m2), as a function of overhang ratio- 22 June,
North orientation
2
W/m
180
9:00
12:00
150
15:00
17:00
120
90
60
No direct solar radiation
incident on window
30
0
0
0.4
0.6
0.8
1
1.4
Direct solar radiation incident on
window
0
0.4
0.6
0.8
1
1.4
Diffuse solar radiation incident
on window
0
0.4
0.6
0.8
1
1.4
Transmitted and reconducted
solar heat gain through window
Overhang ratio
Figure 5.11: Direct, diffuse solar radiation incident on window, and transmitted
and re-conducted solar heat gain (W/m2), as a function of overhang ratio- 24
September, North orientation
181
2
W/m
160
9:00
140
12:00
120
15:00
17:00
100
80
60
40
No direct solar radiation
incident on window
20
0
0
0.4
0.6
0.8
1
1.4
Direct solar radiation incident on
window
0
0.4
0.6
0.8
1
1.4
Diffuse solar radiation incident
on window
0
0.4
0.6
0.8
1
1.4
Transmitted and reconducted
solar heat gain through window
Overhang ratio
Figure 5.12: Direct, diffuse solar radiation incident on window, and transmitted
and re-conducted solar heat gain (W/m2), as a function of overhang ratio- 21
December, North orientation
The diffuse solar radiation indicated a higher value compared to the direct
solar radiation incident on window, on north orientation. The profile pattern of
radiation reduction with the increase of horizontal overhang ratio had a similar
pattern during all four hours considered. However, the maximum amount of diffuse
solar radiation was received during 12:00 and 15:00 hours. This implies that on
north facing façade, the impact of diffuse solar radiation is the main source of
insolation. Also this is clearly evident that higher amount of diffuse radiation is
received when the sun is at higher altitudes and when the direct sunlight is totally
blocked.
The fundamental principles remain the same for the solar heat gain into the
building, where the higher heat gains were indicated during 12:00 and 15:00 hours.
The profile pattern of heat gain reduction with the increase of horizontal overhang
ratio had similar pattern with diffuse solar insolation. But on 22 June, the profile of
heat gain for 9:00, 12:00, and 15:00 hours exhibited deeper curve than on the other
three days. This is mainly due to the impact of heat gain from the direct solar
radiation incident on the window.
182
5.1.4 South Orientation
Direct solar radiation incident on the window is evident on 21 March, 24
September and 21 December on south oriented façade (figure 5.13 to 5.16). A high
amount of direct solar radiation incident on the window surface occurs at 12:00 on
the correspondence dates. However, on 21 December, it exhibits the maximum
incident values as the sun is at the south equinox. A horizontal overhang ratio of 0.4
can block the direct solar radiation from further penetrating into the building on 21
March and 24 September. On 21 December the graph exhibits that, a horizontal
overhang ratio of 0.6 can cut-off the direct solar radiation at 12:00 and 15:00 hours
when the sun is at higher altitudes. Further, increasing the overhang ratio beyond 0.8
had lesser effect in reducing the direct solar radiation incident on the window for
lower solar altitudes (9:00 and 17:00 hours).
The reduction pattern of the diffuse radiation with the increase of horizontal
overhang ratio had a similar profile on all four hours considered (figure 5.13 to 5.16).
The maximum values were obtained during 12:00 and 15:00 hour of the day.
2
W/m
240
9:00
210
12:00
180
15:00
17:00
150
120
90
60
30
0
0
0.4
0.6
0.8
1
1.4
Direct solar radiation incident on
window
0
0.4
0.6
0.8
1
1.4
Diffuse solar radiation incident
on window
0
0.4
0.6
0.8
1
1.4
Transmitted and reconducted
solar heat gain through window
Overhang ratio
Figure 5.13: Direct, diffuse solar radiation incident on window, and transmitted
and re-conducted solar heat gain (W/m2), as a function of overhang ratio- 21 March,
South orientation
183
2
W/m
180
9:00
12:00
150
15:00
17:00
120
90
No direct solar radiation
incident on window
60
30
0
0
0.4
0.6
0.8
1
1.4
Direct solar radiation incident on
window
0
0.4
0.6
0.8
1
1.4
Diffuse solar radiation incident
on window
0
0.4
0.6
0.8
1
1.4
Transmitted and reconducted
solar heat gain through window
Overhang ratio
Figure 5.14: Direct, diffuse solar radiation incident on window, and transmitted
and re-conducted solar heat gain (W/m2), as a function of overhang ratio- 22 June,
South orientation
2
W/m
210
9:00
12:00
180
15:00
17:00
150
120
90
60
30
0
0
0.4
0.6
0.8
1
1.4
Direct solar radiation incident on
window
0
0.4
0.6
0.8
1
1.4
Diffuse solar radiation incident
on window
0
0.4
0.6
0.8
1
1.4
Transmitted and reconducted
solar heat gain through window
Overhang ratio
Figure 5.15: Direct, diffuse solar radiation incident on window, and transmitted
and re-conducted solar heat gain (W/m2), as a function of overhang ratio- 24
September, South orientation
184
2
W/m
450
9:00
12:00
375
15:00
17:00
300
225
150
75
0
0
0.4
0.6
0.8
1
1.4
Direct solar radiation incident on
window
0
0.4
0.6
0.8
1
1.4
Diffuse solar radiation incident
on window
0
0.4
0.6
0.8
1
1.4
Transmitted and reconducted
solar heat gain through window
Overhang ratio
Figure 5.16: Direct, diffuse solar radiation incident on window, and transmitted
and re-conducted solar heat gain (W/m2), as a function of overhang ratio- 21
December, South orientation
The profile pattern of solar heat gain reduction with the increase of horizontal
overhang ratio had a similar pattern with diffuse solar insolation for 21 March, 22
June and 24 September. The lesser curve pattern indicated that the horizontal over
hang had lesser impact in reducing the heat gain from diffuse solar radiation. On 21
December the heat gain profile indicated significant decrease at overhang ratio of 0.4
(figure 5.16). Increase in horizontal overhang ratio beyond 0.6 (12:00 hour) and 0.8
(9:00, 15:00, and 17:00 hour) reduced the heat gain gradually in south orientated
office room.
5.1.5 Influence of Solar Radiation Components on Base Case Model
The direct and diffuse incident solar radiation and the transmitted solar heat
gain through the window glass pane are evaluated for the base case model on
respective orientations. This enables to understand the contribution of each solar
radiation component on the overall heat transmittance into the building. The analysis
185
is done based on one year of the cumulative sum of the direct, diffuse and
transmitted heat gains obtained from the simulation ( table 5.1& figure 5.17).
Each solar radiation component (direct, diffuse and transmitted heat gain)
was compared with total incident solar radiation (direct + diffuse) on respective
facades. The results showed that influence of the diffuse component is high on all
orientations than the direct component of solar radiation incident on the window
pane. Although the west orientation received the highest amount of diffuse solar
radiation (560.73 kW/m2, 62.7%), the north orientation indicated a higher percentage
(75.9%) of diffuse solar radiation compared to total incident solar radiation.
However, the north orientation received the lowest amount of diffuse solar radiation
(477.25 kW/m2). In comparison, the amount of diffuse solar radiation on the east,
north and south received 7.3%, 14.8% and 10.4% less than the west orientation. This
indicates that the influence of the diffuse incident solar radiation had little effect on
the window orientation.
Table 5.1: Summary of cumulative direct and diffuse solar radiation incident and
total transmitted heat gain for base case model with percentage values compared to
total incident solar radiation on bare window
Incident Direct
Solar Radiation
%
kW/m2
Incident Diffuse
Solar Radiation
kW/m2
%
East
370.36
41.6
519.43
58.4
677.54
76.1
West
333.57
37.3
560.73
62.7
680.77
76.1
North
151.40
24.1
477.25
75.9
444.61
70.7
South
191.59
27.6
501.91
72.4
494.86
71.4
Orientation
Total Transmitted
Solar Heat Gain
kW/m2
%
The total amount of direct solar radiation received on the east is higher than
other orientations (370.36 kW/m2). This is about 41.6% of the total incident solar
radiation on the east window surface. In comparison, the amount of direct solar
radiation on the west, north and south received 9.9%, 59.1% and 48.3% less than the
east orientation. The influence of the direct solar radiation on the north is about 21%
less than the south orientation. This indicates that the effect of direct solar radiation
is high on the east and west orientations than on the north and south window pane.
186
The total incident solar radiation on respective orientations showed that the
west (894.3 kW/m2) and east (889.79 kW/m2) received the highest amount of solar
radiation than north (628.64 kW/m2) and south (693.50 kW/m2) window panes
(figure 5.17). In comparison, the east and west oriented window pane transmitted
about 76.1% while north and south transmitted 70.7% and 71.4% of the total incident
radiation, respectively. However, the west and east received the highest amount of
transmitted heat than north and south orientations. The transmitted heat gains on the
north and south oriented window were 34.6% and 27.3% less than the east and west
orientations. Hence, the orientation of the window effect the amount of heat
2
Cumulative Solar Radiation W/m X 1000
transmitted into the building.
1000
900
800
700
600
500
400
300
200
100
0
East
West
Direct Incident Solar Radiation
Total Incident Solar Radiation
Orientation
North
South
Diffused incident Solar Radiation
Total Transmitted Heat Gain
Figure 5.17: Cumulative direct, diffuse and total incident solar radiation and total
transmitted heat gains for base-case model with bare window- East, West, North and
South orientations
The intensity of direct solar radiation incident on the bare window is high on
east orientation, while the north received the minimum intensity of direct solar
radiation on the bare window (figure 5.18). Comparatively, the west, north and south
received 16%, 76%, and 44% less intensity of direct solar radiation than on the east
window. Also the results indicated that the intensity of incident direct radiation is
high during morning hours on the east orientation than in the evening hours on the
west orientation.
187
The west window received the maximum intensity of diffuse solar radiation
compared to other orientations (figure 5.18). The results also showed that the east
and south obtained similar values and north window had the least impact of diffuse
solar radiation on the base case model. Further, the intensity of diffuse solar
radiation is generally high when the intensity of direct component is low and vice
versa. However, the intensity of the diffuse solar radiation is high during the evening
hours on the west than in the morning on the east oriented aperture (which is about
330 W/m2). Table 5.2 illustrates the percent of the direct and diffuse solar radiation
intensity on the base case aperture. Although north indicated the maximum
percentage, the intensity of diffuse solar radiation received was low, which is about
198 W/m2.
Table 5.2: Summary of maximum intensity of direct and diffuse solar radiation
incident and total transmitted heat gain through bare window on east, west, north and
south orientations
% Total
transmitted
heat gain
Orientation
% Direct incident
radiation
% Diffuse incident
radiation
East
70 (502.7 W/m2)
30 (214.9 W/m2)
70 (501.7 W/m2)
West
56 (421.1 W/m2)
44 (328.4 W/m2)
83 (619.6 W/m2)
North
37.5 (118.2 W/m2)
62.5 (197.6 W/m2)
71 (223.3 W/m2)
South
57 (282.4 W/m2)
43 (211.5 W/m2)
87 (427.5 W/m2)
The maximum intensity of transmitted and re-conducted heat gains through
base case window pane were obtained on the west than on the east orientation, while
north window transmitted the least amount of heat (figure 5.18). The transmitted
heat gains were compared with intensity of total incident solar radiation (direct +
diffuse) (table 5.2). The results indicated 87% of the incident solar radiation was
transmitted through the south window, while the west window transmitted 83% of
incident solar radiation. However, west obtained the highest intensity, while north
indicated the lowest intensity for transmitted heat gains (table 5.2). In comparison,
the east, north and south indicated 19%, 63% and 31% less than the west in terms of
heat gain through the base case window. It is mainly due to two reasons. First, the
north façade only receives direct solar radiation between May and August when the
sun is in the north hemisphere. Secondly, the intensity of the solar radiation is low
188
during this period as the distance between the earth and the sun is farthest.
Therefore, the path of the radiation through the atmosphere is long, thus the solar
radiation intensity is reduced due the atmospheric depletion.
2
Solar Radiation Intensity (W/m )
800
700
600
500
400
300
200
100
0
East
West
North
South
Orientation
Direct Incident Solar Radiation
Diffuse Incident Solar radiation
Total Incident Solar Radiation
Total Transmitted Heat Gain
Figure 5.18: Maximum intensity of direct and diffuse incident solar radiation and
total transmitted heat gain for base-case model- East, West, North and South
orientations
5.1.6 Impact of Overhang on Direct Solar Radiation Incident on Window
Figure 5.19 illustrates effectiveness of each horizontal overhang ratio in
reducing the amount direct solar radiation incident on the window surface for the
respective orientations. The calculations were compared to incident direct solar
radiation on the bare window on respective orientations. The east and west
orientations had similar profile of the relationship between the overhang ratio and the
reduction percentage. In both cases, increase in overhang ratio indicated reduction of
incident direct solar radiation. According to the east profile, an overhang ratio of 1.0
reduced the incident direct solar radiation by about 77% and maximum of about 90%
reduction can be achieved with an overhang ratio of 1.6. Increase in overhang ratio
beyond 1.6 had lesser impact on reducing the direct solar radiation incident on the
east window pane.
189
The west orientation profile indicates a lower gradient than the east profile.
This implies that on the west orientation, the increase of horizontal overhang ratio
had a lesser impact on the amount of incident direct solar radiation than on the east
orientation. The west profile in figure 5.19 illustrates that horizontal overhang ratios
of 1.0 and 1.6 reduced 70% and 81% of incident direct solar radiation respectively.
Incident direct solar radiation reduction profile indicated a similar profile for
the north and south orientations (figure 5.19). The profile value for both north and
south oriented overhang ratio of 0.6 and 0.8 indicated about 84% reduction of
incident direct solar radiation. Also an increase in horizontal overhang beyond the
above ratio (OHR 0.6 on north and 0.8 on south) indicated no further impact on
reduction of the direct solar radiation incident on window. However, the south
profile showed a lesser gradient than the north, which means that north oriented
Cumulative Incident Direct Solar Radiation Reduction
(%)
window blocked more incident direct solar radiation than the south oriented window.
100
90
80
70
60
50
40
30
20
10
0
0
0.2
0.4
0.6
0.8
1
1.2
1.4
1.6
1.8
Overhang ratio
East
West
North
South
Figure 5.19: Reduction percentage (%) of cumulative amount of direct solar
radiation incident on window surface as function of horizontal overhang ratio- East,
West, North and South orientations
The analysis indicated that the east (OHR 1.2) and west (OHR 1.6)
orientations needed larger horizontal overhang ratios in order to reduce direct solar
190
radiation incident on the window pane by more than 80%. For north and south
orientations the maximum shading from direct solar radiation can be achieved by
overhang ratios of 0.6 and 0.8 respectively. This implies that horizontal overhang
depth in order to cut-off the maximum amount of direct solar radiation incident on
the window surface largely depends on the orientation of the correspondence window
surface. Further, the west oriented window received maximum amount of direct
solar radiation on the window pane even when solar shading were applied compared
to all other orientations considered. On the other hand, the north orientation had the
minimum impact of direct solar radiation incident on the window.
5.1.7 Impact of Overhang on Diffuse Solar Radiation Incident on Window
Figure 5.20 illustrates the reduction percentages of cumulative diffuse solar
radiation incident on the window when horizontal solar shading devices were
applied. The west orientation indicated the highest reduction percentage for all tested
overhangs. Initially, at horizontal overhang ratio of 0.4 indicated, 22.7%, 23.5%,
21.8% and 22.4% reduction on the east, west, north and south orientations compared
to the bare window. For horizontal overhang ratio 1.0 were able to cut off almost
about 38.8%, 40.1%, 37.2% and 38.2% on the east, west, north and south
orientations respectively.
Increase in horizontal overhang ratio from 1.0 to 1.4 on the north and south
orientations could only reduced 5% of the incident diffuse solar radiation. Increase
of horizontal overhang ratio from 1.0 to 1.6 could reduce about 7% of diffuse solar
radiation on both east and west orientations. Further increase in overhang ratio had a
lesser impact on the amount of diffuse solar radiation received on the window pane.
Hence, the results indicated that use of maximum overhang ratios (east/ west OHR of
1.6 and north/ south OHR of 1.4) on all orientations could reduce less than 50% of
the incident diffuse solar radiation on the bare window.
191
Cumulative Incident Diffused Solar Radiation
Reduction (%)
50
45
40
35
30
25
20
15
10
5
0
0
0.2
0.4
0.6
0.8
1
1.2
1.4
1.6
1.8
Overhang ratio
East
West
North
South
Figure 5.20: Reduction percentage (%) of cumulative amount of diffuse solar
radiation incident on window surface as function of horizontal overhang ratio- East,
West, North and South orientations
5.1.8 Impact of Overhang on Transmitted and Re-Transmitted Solar Heat Gain
through Window System
The reduction percentage of transmitted and re-conducted heat gain is
calculated and compared to the total incident (direct and diffuse) solar radiation on
the bare window. The profile showed a similar pattern for all orientations considered
(figure 5.21). Initially the bare window indicated heat gain reduction between 23.9%
and 29.3% on the east, west, north and south orientations compared to the total
incident solar radiation on the window surface. In other words, more than 76% to
70% of incident energy was transmitted through the glazing of the bare window.
When the horizontal over hang ratio is of 1.0, the total heat gain reduction was about
41.4%, 38.7%, 33% and 35.4% on the east, west, north and south orientations
compared to heat gain through the bare window. Horizontal overhang ratio of 1.4 for
the north and south indicated 35.9% and 38.3% of total heat gain reduction
respectively compared to heat gain through the bare window. Similarly, the overhang
192
ratio of 1.6 on the east and west indicated 48.9% and 45.4% of total heat gain
reduction compared to without overhang base case model.
When horizontal overhang is applied, the orientation of the window had
lesser impact on the total heat gain into the space considered. The reason can be
stated as mainly due to the obstruction of direct solar radiation incident on the
window surface by the external shading device, which indicated different intensity
levels for different orientations. Also the horizontal overhang had lesser impact on
diffuse solar radiation incident on the window surface, except on the west
orientation. Therefore, the heat gain from direct solar radiation reduced significantly
while heat gain from diffuse solar radiation had lesser reduction. Hence heat gain
from diffuse solar radiation dominated compared to the heat gain from direct solar
radiation into the space, when the window was shaded with horizontal overhang.
This was evident in the profile patterns of diffuse solar radiation incident on the
window and total heat gain, which exhibited a similar profile for the east, west, north
Cumulative Transmitted Solar Radiation Reduction (%)
and south orientations.
80.0
70.0
60.0
50.0
40.0
30.0
20.0
10.0
0.0
0
0.2
0.4
0.6
0.8
1
1.2
1.4
1.6
1.8
Overhang ratio
East
West
North
South
Figure 5.21: Reduction percentage (%) of cumulative transmitted and reconducted solar heat gain in an office room space as function of horizontal overhang
ratio- East, West, North and South orientations
193
5.1.8.1 Hourly Variation of Transmitted and Re-Transmitted Solar Heat Gain
through Window System
The effects of hourly variations of each shading device on the total solar heat
gain were assessed with respect to the main cardinal orientations. The maximum
total solar heat gains were obtained for each hour on the selected design days (21
March, 22 June, 24 September and 21 December) (figure 5.22 to 5.25).
Figure 5.22 illustrates that, significant amount of heat gain was obtained in
the morning hours between 8:00 am and 12:00 noon for the east orientation (for the
base-case bare window option). During these hours, the direct sunlight incident was
on the east façade and after 13:00 hour, the sun is behind the window pane, thus the
heat gains were very low in the afternoon hours. The maximum heat gain was
indicated at 9:00 hour, but when overhangs were applied two variations can be
observed. Firstly, the peak hour point shifts from 9:00 hour towards 8:00 hour.
Secondly, as the overhang ratio increases, the intensity of the peak solar heat gain
was reduced.
500
2
Solar Heat Gain Factor (W/m )
600
400
300
200
100
0
7
8
9
10
11
12
13
14
15
16
17
18
Hour
ohr 0
ohr 0.4
ohr 0.6
ohr 0.8
ohr 1.0
ohr 1.4
ohr 1.6
Figure 5.22: Maximum hourly total solar heat gains for tested overhang ratiosEast orientation
194
700
2
Solar Heat Gain Factor (W/m )
600
500
400
300
200
100
0
8
9
10
11
12
13
14
15
16
17
18
19
Hour
ohr 0
ohr 0.4
ohr 0.6
ohr 0.8
ohr 1.0
ohr 1.4
ohr 1.6
Figure 5.23: Maximum hourly total solar heat gains for tested overhang ratiosWest orientation
300
2
Solar Heat Gain Factor (W/m )
250
200
150
100
50
0
7
8
9
10
11
12
13
14
15
16
17
18
Hour
ohr 0
ohr 0.4
ohr 0.6
ohr 0.8
ohr 1.0
ohr 1.4
Figure 5.24: Maximum hourly total solar heat gains for tested overhang ratiosNorth orientation
195
450
2
Solar Heat Gain Factor (W/m )
400
350
300
250
200
150
100
50
0
7
8
9
10
11
12
13
14
15
16
17
18
Hour
ohr 0
ohr 0.4
ohr 0.6
ohr 0.8
ohr 1.0
ohr 1.4
Figure 5.25: Maximum hourly total solar heat gains for tested overhang ratiosSouth orientation
According to figure 5.23, heat gain pattern on the west is similar to east
orientation but on the opposite direction. The maximum solar heat gains were
obtained during afternoon between 14:00 and 18:00 hours. As overhang ratio was
increased from of 0.4 to 1.0, the peak hour shifts from 16:00 hour towards 18:00
hour and also reduced the intensity of the heat gain at peak hour. These patterns are
mainly due to the effects of heat gains from direct solar radiation. Increasing the
overhang depth reduces the optimum incident angle for maximum solar radiation
transmittance, thus shifts the solar position to lower solar altitudes. As a result the
amounts of solar radiation received at optimum incident angle were also reduced.
North and south orientation illustrated two different profiles of hourly total
solar heat gains compared to the east and west orientations (figure 5.24 & 5.25).
According to figure 5.24, the north orientation obtained a constant amount of heat
gain for considerable number of hours; 9:00 to 16:00 hours, for overhang ratios
between 0.4 and 1.4. This profile was maintained even when different shading
depths were applied. Also, the solar heat gain intensity is reduced with the increase
of overhang ratio. This profile pattern is due to the effects of diffuse solar radiation,
while direct solar radiation has little effect on the north façade.
196
Figure 5.25 illustrates the total solar heat gain profile for the south oriented
window. The results indicated that the peak heat gains through the bare window
occur at noon time, when the sun is at higher altitude. Thus, maximum amount of
direct solar radiation penetrates through the window pane at high incident angle.
Therefore, introduction of overhang with smaller projections (with overhang ratio
0.4), were able to terminate considerable amount of direct solar radiation incident on
the window (which also reflects in the changing patterns of solar heat gain profiles).
On the south façade, application of horizontal overhang, terminates the peak solar
heat gain and changes into constant heat gains profile throughout the day, between
9:00 and 16:00 hours, for overhang ratios between 0.6 and 1.4. Therefore, the north
and south oriented office room has a constant thermal performance on most hours of
the day.
The effects of external horizontal shading devices on hourly total solar heat
gains for different orientations illustrated three profile patterns of solar heat gains:
o
The peak hour of heat gain shift outside the working hour time (9:00 to
17:00) on the east and west orientations.
o
Application of overhang maintained a constant amount of heat gain for
considerable number of hours (9:00 to 16:00) for respective overhang ratios
on the north and south orientations.
o
Increase of overhang depth reduced the intensity of the maximum heat gain.
On east and west orientations, the peak heat gain hour shift beyond the
working hour time frame and reduced the intensity of the heat gains with the increase
of overhang ratio (or increase of overhang depth). For instance, on the east oriented
office room, application of the shading device with a depth similar to the height of
the window (overhang ratio 1.0) shifts the peak heat gain from 9:00 hour to 8:00
hour. Similar overhang projection on the west façade shifts the peak heat gain from
16:00 hour to 18:00 hour, compared to the maximum heat gain through the bare
window on the respective orientation. Thereby it can be suggested, as energy
efficient measures, the working hours can be adjusted based on the overhang depth.
For instance, on the east and west oriented office rooms, their respective working
197
hours can be adjusted from 10:00 to18:00 hours and 8:00 to 16:00 for overhang ratio
of 1.0. Even if the air-conditioning system is switched on one hour before and
switched off one hour after the working hours, this will avoid the peak heat gain hour
of the day. As a result it may reduce the building cooling loads considerably as well
as the initial start-up loads in the morning on the east oriented office rooms.
5.2 Absolute Work Plane Illuminance
The horizontal solar shading is used to reduce the heat gain into the building
and cut down the cooling load of the space. However, this may have an adverse
effect on the amount of natural light penetrating into the building, which may result
in use of artificial lighting.
The absolute work plane illuminance (direct sunlight + sky light) were
calculated for the correspondence external horizontal overhangs. The results were
obtained for four days (21 March, 22 June, 24 September and 21 December), at four
times within general office working hours (9:00, 12:00, 15:00 and 17:00 hours) and
on the main cardinal orientations (East, West, North and South). The two
correspondence reference points; reference point 01 (Ref.Pt 01) at 3.0 meter and
reference point 02 (Ref.Pt 02) at 5.7 meter, were positioned along the center of the
6.0 meter deep office room at the work plane height of 0.9 meter. The evaluation of
natural-light quantity is based on the target absolute work plane illuminance at
500lux. The correspondence transmitted and re-conducted solar heat gains were also
presented for better understanding of the relationship between the illuminance level
and heat gains, when horizontal shading devices were applied. The analysis is based
on the maximum, minimum and mean values calculated for both absolute work plane
illuminance at the two reference points and the correspondence transmitted solar heat
gain.
198
5.2.1 East Orientation
Solar heat gain (W/m2)
Illuminance(lux)
6500
450
9:00
6000
400
5500
5000
4500
12:00
350
15:00
300
17:00
4000
3500
250
3000
200
2500
150
2000
1500
100
1000
500
50
Target Illuminance
0
0
0 0.4 0.6 0.8 1 1.4 1.6
0 0.4 0.6 0.8 1 1.4 1.6
Light Reference Pt. 01
Light Reference Pt. 02
0 0.4 0.6 0.8 1 1.4 1.6
Overhang ratio
Figure 5.26: Absolute work plane illuminance (lux) at ref.pt:01, ref.pt:02, and
solar heat gain (W/m2), as a function of overhang ratio- 21 March, East orientation
2
Illuminance(lux)
Solar heat gain (W/m )
6000
300
5500
275
5000
250
4500
225
4000
200
3500
175
3000
150
2500
9:00
12:00
15:00
17:00
125
Target Illuminance
2000
100
1500
75
1000
50
500
25
0
0
0
0.4 0.6 0.8
1
1.4 1.6
Light Reference Pt. 01
0
0.4 0.6 0.8
1
1.4 1.6
0
0.4 0.6 0.8
1
1.4 1.6
Light Reference Pt. 02
Overhang ratio
Figure 5.27: Absolute work plane illuminance (lux) at ref.pt:01, ref.pt:02, and
solar heat gain (W/m2), as a function of overhang ratio- 22 June, East orientation
199
Illuminance(lux)
Solar heat gain (W/m2)
2500
240
9:00
2250
210
12:00
180
15:00
2000
1750
17:00
150
1500
1250
120
1000
90
750
60
500
Target Illuminance
30
250
0
0
0
0.4 0.6 0.8 1
1.4 1.6
Light Reference Pt. 01
0 0.4 0.6 0.8
1
1.4 1.6
0
0.4 0.6 0.8
1 1.4 1.6
Light Reference Pt. 02
Overhang ratio
Figure 5.28: Absolute work plane illuminance (lux) at ref.pt:01, ref.pt:02, and
solar heat gain (W/m2), as a function of overhang ratio- 24 September, East
orientation
Illuminance
(lux)
2
Solar heat gain (W/m )
11000
550
10000
500
9000
450
8000
400
7000
350
6000
300
5000
250
4000
200
9:00
12:00
15:00
3000
2000
17:00
150
Target Illuminance
100
1000
50
0
0
0 0.4 0.6 0.8 1 1.4 1.6
0 0.4 0.6 0.8 1 1.4 1.6
Light Reference Pt. 01
Light Reference Pt. 02
0 0.4 0.6 0.8 1 1.4 1.6
Overhang ratio
Figure 5.29: Absolute work plane illuminance (lux) at ref.pt:01, ref.pt:02, and
solar heat gain (W/m2), as a function of overhang ratio- 21 December, East
orientation
200
The maximum illuminance was obtained at 9:00 hour at both reference points
except in September, when the window is facing the east (figure 5.26 to 5.29). The
results indicated a significant difference between illuminance values obtained at 9:00
and 12:00 hours at reference point 01 for all horizontal overhang ratios on 21 March,
22 June, and 21 December. This is mainly due to the direct sunlight penetration into
the building during the respective hours. At 12:00 hour, increase of horizontal
overhang ratio reduced the amount of direct sunlight penetrating into the space as the
sun is at a higher altitude at that particular hour. At reference point 02 the
illuminance profile indicated a similar pattern on all three days except on 24
September, which means that increase in horizontal overhang ratio reduces the direct
sun light patches at the back of the space. The comparison results between
illuminance values and correspondence heat gains showed a direct correlation
between the two components, where maximum heat gains and illuminance indicated
similar pattern during the same hours (figure 5.26 to 5.29).
On 24 September, the maximum illuminance was obtained at 12:00 noon at
both reference points (figure 5.28). This is due to an effect on the external
illuminance at that particular time. At 9:00 hour, the external diffuse illuminance is
dominant, while at 12:00 noon the illuminance by the direct sun is dominant (see
figure 2.13, Chapter 2). Hence, the direct sunlight had higher illuminance than the
diffuse component of the sky. Therefore, the illuminance profile indicated a similar
pattern for all hours at correspondence reference points on 24 September. At
reference point 01, the profile showed a steeper gradient with the increase of
horizontal overhang ratio, while at reference point 02 indicated a lesser gradient.
However at 9:00 maximum heat gain was indicated when solar shading is not applied
(bare window).
Table 5.3a & b, shows the maximum, minimum and mean values obtained for
illuminances at each reference points and correspondence solar heat gains. On 22
June and 21 December, reference point 01 obtained the minimum illuminance that is
below the target level (500 lux), for overhang ratio of 0.4 and 0.8 and above
respectively. Reference point 02 obtained minimum illuminance below the target
level on 22 June and 21 December, for all correspondence overhang ratios. On the
201
above two days, the sun is in the solstice and less direct sunlight penetrates into the
space. On 21 March and 24 September, deep end of the office room obtained a
minimum illuminance below the target level for overhang ratio of 1.4 and 0.4 and
above respectively. Increase of horizontal overhang ratio from 1.0 to 1.4 on 21
March reduced the minimum illuminance level by about 5%, compared to the target
illuminance level (500 lux) at reference point 02.
The correspondence minimum solar heat gain indicated 41% reduction
compared to the base case heat gain (window without external shading device), at
overhang ratio of 1.4. Hence, when the illuminance is 477 lux, the correspondence
heat gain was 61 W/m2. On 24 September, overhang ratio of 0.4 received a
minimum illuminance of 491 lux and the heat gain obtained was 60 W/m2. The
minimum solar heat gain (22 W/m2) and illuminance level (166 lux) were indicated
for overhang ratio of 1.6 on 22 June.
The mean work plane illuminance below 500 lux was indicated for overhang
ratio of 1.0 and 1.6 at reference point 02, on 24 September and 21 December
respectively (table 5.3 b). The correspondence maximum heat gains for overhang
ratio of 1.0 indicated 59%, 58%, 53% and 68% reduction compared to the base case
option on 21 March, 22 June, 24 September and 21 December respectively.
However, increase of overhang ratio up to 1.6 indicated 73%, 73%, 56% and 82%
reduction of the maximum solar heat gain compared to the base case model on 21
March, 22 June, 24 September and 21 December respectively. Thus, the mean work
plane illuminance values were reduced up to 697 lux, 534 lux, 371 lux, and 485 lux
for overhang ratio 1.6 at reference point 02 on 21 March, 22 June, 24 September and
21 December respectively (table 5.3 a & b). In general, an overhang ratio of 1.6 on
the east orientated window may still provide over 300 lux of illuminance which is
adequate for general lighting of an office space.
202
Table 5.3a: Maximum, minimum and mean work plane illuminance values at ref.
pt: 01, ref. pt: 02, and total solar heat gain- 21 March and 22 June, East orientation
OHR
(PF)
Total Illuminance (Sunlight & Daylight)(lux) at Reference Pt:01
21-Mar
22-Jun
Maxm % Minm % mean % Maxm % Minm % mean
0
6015
0 1693 0 2299 0
5249
0
638
0 2153
5254 13 1206 29 1556 32 4202 20 477 25 1528
0.4
0.6
5076 16 1147 32 1478 36 4054 23 459 28 1454
0.8
4701 22 937 45 1248 46 3545 32 381 40 1208
1
4536 25 898 47 1204 48 3409 35 368 42 1165
1.4
4222 30 751 56 1042 55 2982 43 309 52 979
1.6
4146 31 712 58 999 57 2865 45 293 54 925
OHR
Total Illuminance (Sunlight & Daylight)(lux) at Reference Pt.02
(PF)
21-Mar
22-Jun
Maxm % Minm % mean % Maxm % Minm % mean
0
1942
0
826
0 1342 0
1893
0
308
0 1092
0.4
1590 18 696 16 994 26 1595 16 265 14 861
0.6
1414 27 636 23 916 32 1448 23 246 20 787
0.8
1207 38 568 31 841 37 1246 34 218 29 701
1
1044 46 529 36 798 41 1109 41 206 33 658
912
52 182 41 586
1.4
853
56 477 42 740 45
1.6
778
60 438 47 697 48
797
58 166 46 534
OHR
Total solar heat gain (Transmitted & re-conducted) (W/m2)
(PF)
21-Mar
22-Jun
Maxm % Minm % mean % Maxm % Minm % mean
0
392
0
104
0
248
0
267
0
44
0
156
0.4
287
27
82
21 184 26
190
29
33
25 111
0.6
242
38
75
28 158 36
160
40
30
33
95
0.8
201
49
70
33 135 45
134
50
27
39
80
66
36 114 54
25
43
68
1
162
59
111
58
75
72
23
49
49
1.4
107
73
61
41
84
66
104
73
59
43
82
67
1.6
71
73
22
51
46
%
0
29
32
44
46
55
57
%
0
21
28
36
40
46
51
%
0
29
39
48
56
69
70
203
Table 5.3b: Maximum, minimum and mean work plane illuminance values at ref.
pt: 01, ref. pt: 02, and total solar heat gain- 24 September and 21 December, East
orientation
OHR
(PF)
Total Illuminance (Sunlight & Daylight)(lux) at Reference Pt:01
24-Sep
21-Dec
Maxm % Minm % mean % Maxm % Minm % mean
0
2179
0 1263 0 1912 0 10460 0
905
0 1608
0.4
1419 35 888 30 1361 29 9939
5
634 30 1086
0.6
1351 38 841 33 1273 33 9713
7
600 34 1034
1156 47 679 46 1032 46 9457 10 483 47 868
0.8
1
1119 49 649 49 966 49 9248 12 461 49 833
1.4
982
55 535 58 795 58 9067 13 379 58 720
1.6
946
57 504 60 754 61 9016 14 357 61 691
OHR
Total Illuminance (Sunlight & Daylight)(lux) at Reference Pt.02
(PF)
24-Sep
21-Dec
Maxm % Minm % mean % Maxm % Minm % mean
0
1370
0
592
0
916
0
2418
0
420
0
947
0.4
948
31 491 17 733 20 1967 19 348 17 701
0.6
881
36 444 25 647 29 1742 28 314 25 649
0.8
818
40 392 34 551 40 1515 37 275 34 591
781
43 362 39 485 47 1305 46 254 39 556
1
1.4
734
46 321 46 412 55 1144 53 225 46 515
697
49 291 51 371 59 1092 55 202 52 485
1.6
OHR
Total solar heat gain (Transmitted & re-conducted) (W/m2)
(PF)
24-Sep
21-Dec
Maxm % Minm % mean % Maxm % Minm % mean
0
226
0
79
0
152
0
502
0
59
0
280
0.4
161
29
60
24 111 27
361
28
45
25 203
0.6
136
40
54
31
95
38
294
41
40
33 167
0.8
114
49
50
37
82
46
227
55
37
38 132
47
41
77
50
34
42
98
1
106
53
162
68
1.4
100
56
43
46
71
53
94
81
31
48
62
1.6
98
56
41
48
70
54
92
82
30
50
61
%
0
32
36
46
48
55
57
%
0
26
32
38
41
46
49
%
0
28
41
53
65
78
78
5.2.1.1 Window Height to Room Depth Ratio-East Orientation
The mean work plane illuminance values were plotted against overhang ratio
to determine a general distribution profile of illuminance levels received at respective
reference points for the tested overhang ratios (figure 5.30 and 5.31). The maximum
mean work plane illuminance was received on 21 March. This is mainly due to the
204
higher global exterior illuminance by direct sunlight received during morning hours
(8:00 to 11:00 hour) on this day, than on other three design days considered (refer
Chapter 2). The lowest mean values were received on 21 December at reference
point 01. Hence, internal illuminance level at reference point 01 was affected by the
amount of direct sunlight received.
Mean work plane illuminance (lux)
2500
2000
1500
1000
500
0
0
0.2
0.4
0.6
0.8
1
1.2
1.4
1.6
Overhang ratio
21-Mar
22-Jun
24-Sep
21-Dec
Figure 5.30: Mean work plane illuminance (lux) at reference point 01 for tested
overhang ratio- 21 March, 22 June, 24 September, and 21 December- East
orientation.
Mean work plane illuminanceat (lux)
1500
1250
1000
750
500
250
0
0
0,2
0,4
0,6
0,8
1
1,2
1,4
1,6
Overhang ratio
21-Mar
22-Jun
24-Sep
21-Dec
Figure 5.31: Mean work plane illuminance (lux) at reference point 02 for tested
overhang ratio- 21 March, 22 June, 24 September, and 21 December- East
orientation.
205
The lowest mean work plane illuminances were indicated on the 24
September, at reference point 02. At overhang ratio 1.0, the illuminance level
reached the target level of 500 lux for general office work (figure 5.31).
Figure 5.32: Effect of overhang on natural light distribution in perimeter office
room- East orientation.
Based on above data, the relationship between head height of the window and
natural-light penetration into the room were determined. Assuming the depth of the
overhang is added to the depth (the distance from back of the wall to window wall)
of the room to establish an equivalent room, where the outer edge of the overhang
was treated as the plane of the window wall (figure 5.32). Hence, overhang ratio 1.0
(1.82 meter or 6 ft) gives a total depth of 7.9 meter (26 ft) to the back of the room.
Thus, the ratio between the height of the aperture (1.82 meter or 6 ft from top of the
sill to ceiling) and the depth of the equivalent room (7.9 meter or 26 ft) is 1: 4.3.
Therefore, it can be assumed that the minimum work plane illuminance of 500 lux is
achieved at depth of 4.3 times the head height of the aperture on the east orientation,
under clear sky condition. Although it is a simplified assumption, this gives an idea
that the natural-light penetrates more than the common rule of thumb of about 2.5
times the head height of the aperture, when higher amount of exterior natural-light is
available.
206
5.2.2 West Orientation
Solar heat gain (W/m2)
Illuminance(lux)
12000
650
11000
600
10000
550
12:00
500
15:00
9000
450
8000
9:00
17:00
400
7000
350
6000
300
5000
250
4000
200
3000
150
Target Illuminance
2000
100
1000
50
0
0
0 0.4 0.6 0.8 1 1.4 1.6
0
Light Reference Pt. 01
0.4 0.6 0.8 1 1.4 1.6
0 0.4 0.6 0.8
1 1.4 1.6
Light Reference Pt. 02
Overhang ratio
Figure 5.33: Absolute work plane illuminance (lux) at ref.pt:01, ref.pt:02, and
solar heat gain (W/m2), as a function of overhang ratio- 21 March, West orientation
Solar heat gain (W/m2)
Illuminance(lux)
325
4000
300
3500
3000
2500
9:00
275
12:00
250
15:00
225
17:00
200
175
2000
150
125
1500
100
1000
75
Target Illuminance
500
50
25
0
0
0
0.4 0.6 0.8 1
1.4 1.6
Light Reference Pt. 01
0
0.4 0.6 0.8
1 1.4 1.6
0 0.4 0.6 0.8
1 1.4 1.6
Light Reference Pt. 02
Overhang ratio
Figure 5.34: Absolute work plane illuminance (lux) at ref.pt:01, ref.pt:02, and
solar heat gain (W/m2), as a function of overhang ratio- 22 June, West orientation
207
Illuminance(lux)
2
Solar heat gain (W/m )
7000
425
400
375
350
6000
12:00
325
300
275
5000
15:00
17:00
250
225
200
175
4000
3000
2000
9:00
150
125
100
Target Illuminance
75
50
25
1000
0
0
0 0.4 0.6 0.8 1 1.4 1.6
0 0.4 0.6 0.8 1 1.4 1.6
Light Reference Pt. 01
Light Reference Pt. 02
0 0.4 0.6 0.8 1 1.4 1.6
Overhang ratio
Figure 5.35: Absolute work plane illuminance (lux) at ref.pt:01, ref.pt:02, and
solar heat gain (W/m2), as a function of overhang ratio- 24 September, West
orientation
Illuminance(lux)
2
Solar heat gain (W/m )
255
4500
240
4000
3500
3000
210
12:00
195
180
15:00
165
150
2500
2000
9:00
225
17:00
135
120
105
Target Illuminance
90
1500
75
60
1000
45
30
500
15
0
0
0 0.4 0.6 0.8 1 1.4 1.6
0 0.4 0.6 0.8 1 1.4 1.6
Light Reference Pt. 01
Light Reference Pt. 02
0 0.4 0.6 0.8 1 1.4 1.6
Overhang ratio
Figure 5.36: Absolute work plane illuminance (lux) at ref.pt:01, ref.pt:02, and
solar heat gain (W/m2), as a function of overhang ratio- 21 December, West
orientation
Work plane illuminance values and solar heat gain results for 21 March, 22
June, 24 September and 21 December for the west oriented window are shown in
208
figure 5.33 to 5.36. The maximum illuminance was obtained at 17:00 hour at
reference point 01 for all overhang depths considered. Results at reference point 02
obtained maximum illuminance at different hours of the day; 21 March and 24
September at 17:00 hour, while on 22 June at 15:00 hour. On 21 December almost
similar illuminance values were indicated at 17:00 and 12:00 hours at reference point
02. In the morning, at 9:00 hour, illuminance value resulted below the target level
(500 lux) on 21 March, 24 September and 21 December for all overhang depths at
reference point 02. Overhang ratio of 0.8 and above (up to overhang ratio 1.6)
indicated illuminance value below 500 lux on 22 June.
The illuminance profiles showed a similar pattern on 21 March, 24
September and 21 December (figure 5.33, 5.35 and 5.36) at each reference points.
The results showed a significant difference between illuminance values obtained at
17:00 hour and 15:00 hour at reference point 01 for all overhang depths. The reason
can be explained that the penetration of the direct sunlight into the space occur at low
solar altitudes. Initially, the illuminance level showed sudden reduction with the
introduction of overhang ratio of 0.4 at 15:00 and 12:00 hours and the illuminance
profile had lesser gradient with the increase of overhang ratios at reference point 01
(figure 5.33, 5.35, and 5.36). The reason is that, increase of horizontal overhang
ratio reduced the amount of direct sunlight penetration significantly, but had little
impact on the diffuse component of illuminance. However, based on the profiles for
22 June, the maximum illuminance was shown for the base case model at 15:00 than
at 17:00 hour (figure 5.34). This is an effect of the external illuminance conditions,
where at 15:00 hour illuminance by the direct sun is dominant while at 17:00 hour
the diffuse sky illuminance (clear sky + overcast sky) is dominant (see figure 2.12 in
Chapter 2). Hence, increase of overhang ratio resulted in a deeper gradient
illuminance profile pattern at 15:00 hour than at 17:00 hour.
Illuminance profile at reference point 02 showed a similar pattern with lesser
gradient on 21 March, 24 September and 21 December for all four hours considered.
However, the illuminance profile at 15:00 hour on 22 June indicated a curve pattern
with higher gradients, which means that the direct sun penetrates deep into the room
during this hour and gradually cut-off with the increment of the overhang ratios.
209
Table 5.4 a & b, shows the maximum, minimum and mean values obtained
for illuminances at reference point 01, reference point 02, and correspondence solar
heat gains for the west oriented office room. Increase of overhang ratio from ‘0’ to
1.6 reduced the maximum total solar heat gain by 75%, 73%, 69% and 62%
compared to the heat gain through the base case model wall opening, on 21 March,
22 June, 24 September and 21 December respectively. The minimum work plane
illuminance at reference point 02 for overhang ratio of 0.8 indicated below 500 lux
on 22 June.
Table 5.4a: Maximum, minimum and mean work plane illuminance values at ref.
pt: 01, ref. pt: 02, and total solar heat gain- 21 March and 22 June, West orientation
OHR
(PF)
0
0.4
0.6
0.8
1
1.4
1.6
OHR
(PF)
0
0.4
0.6
0.8
1
1.4
1.6
OHR
(PF)
0
0.4
0.6
0.8
1
1.4
1.6
Total Illuminance (Sunlight & Daylight)(lux) at Reference Pt:01
21-Mar
22-Jun
Maxm % Minm % mean % Maxm % Minm % mean
11147 0
909
0 2599 0
3624
0 1416 0 2636
10241 8
707 22 1734 33 3106 14 1073 24 1895
10021 10 685 25 1610 38 3044 16 1036 27 1775
9600 14 585 36 1335 49 2834 22 866 39 1445
9405 16 569 37 1254 52 2774 23 839 41 1355
9035 19 492 46 1059 59 2585 29 707 50 1091
8935 20 470 48 1015 61 2528 30 669 53 1026
Total Illuminance (Sunlight & Daylight)(lux) at Reference Pt.02
21-Mar
22-Jun
Maxm % Minm % mean % Maxm % Minm % mean
1940
0
686
0
2787
0
481
0 1611 0
945
2338 16 428 11 1154 28 1434 26 596 13 818
2119 24 406 16 1030 36 1243 36 560 18 762
1881 33 368 23 916 43 1046 46 496 28 680
1686 39 352 27 834 48
898
54 468 32 633
1445 48 321 33 748 54
712
63 415 39 553
1344 52 299 38 704 56
631
67 378 45 502
Total solar heat gain (Transmitted & re-conducted) (W/m2)
21-Mar
22-Jun
Maxm % Minm % mean % Maxm % Minm % mean
620
0
68
0
344
0
291
0
86
0
189
468
25
54
22 261 24
170
42
65
24 118
405
35
49
28 227 34
117
60
59
32
88
349
44
46
33 197 43
98
66
54
38
76
298
52
43
37 170 50
91
69
50
42
71
202
40
42 121 65
81
45
47
63
67
72
156
75
38
44
97
72
73
49
78
44
61
%
0
28
33
45
49
59
61
%
0
13
19
28
33
42
47
%
0
38
53
60
63
66
68
210
The mean work plane illuminance for overhang ratio 1.4 on 21 December
indicated below the 500 lux value (table 5.4b). The correspondence maximum solar
heat gain were reduced by 67%, 72%, 63% and 58% compared to base case option
for the overhang ratio of 1.4 on 21 March, 22 June, 24 September and 21 December
respectively. Hence, 21 December indicated lesser reduction compared to other days.
Thus, when the sun is in the south solstice (on 21 December) had lesser impact on
the west oriented window.
Table 5.4b: Maximum, minimum and mean work plane illuminance values at ref.
pt: 01, ref. pt: 02, and total solar heat gain- 24 September and 21 December, West
orientation
OHR
(PF)
0
0.4
0.6
0.8
1
1.4
1.6
OHR
(PF)
0
0.4
0.6
0.8
1
1.4
1.6
OHR
(PF)
0
0.4
0.6
0.8
1
1.4
1.6
Total Illuminance (Sunlight & Daylight)(lux) at Reference Pt:01
24-Sep
21-Dec
Maxm % Minm % mean % Maxm % Minm % mean
6447
0 1104 0 2127 0
4272
0
427
0 1722
5864
9
775 30 1499 30 3878
9
351 18 1223
5752 11 734 34 1413 34 3807 11 341 20 1142
5483 15 592 46 1161 45 3624 15 309 28 939
5389 16 566 49 1103 48 3567 16 302 29 877
5157 20 467 58 926 56 3420 20 280 35 748
5088 21 440 60 882 59 3375 21 273 36 717
Total Illuminance (Sunlight & Daylight)(lux) at Reference Pt.02
24-Sep
21-Dec
Maxm % Minm % mean % Maxm % Minm % mean
1577
0
520
0 1137 0
1128
0
292
0
951
1345 15 430 17 922 19
858
24 271
7
809
1233 22 391 25 836 26
787
30 261 10 727
1106 30 344 34 746 34
711
37 251 14 637
1011 36 317 39 688 39
683
39 244 16 560
879
44 283 46 620 46
647
43 237 19 488
811
49 256 51 576 49
620
45 230 21 448
Total solar heat gain (Transmitted & re-conducted) (W/m2)
24-Sep
21-Dec
Maxm % Minm % mean % Maxm % Minm % mean
386
0
76
0
231
0
229
0
52
0
140
288
25
57
25 173 25
172
25
45
15 108
251
35
51
32 151 34
152
33
42
19
97
220
43
47
38 133 42
135
41
40
22
88
192
50
44
42 118 49
121
47
39
25
80
142
39
48
91
61
28
63
95
58
37
66
119
69
38
50
79
66
86
62
37
29
61
%
0
29
34
45
49
57
58
%
0
15
24
33
41
49
53
%
0
23
31
37
43
53
56
211
5.2.2.1 Window Height to Room Depth Ratio-West Orientation
The mean work plane illuminance at reference point 01 for the west
orientation indicated well over the 500 lux illuminance levels for all overhang ratios
tested (figure 5.37). The highest illuminance levels were shown on 21 March and 22
June, while 21 December indicated lower illuminance values with the increase of
overhang ratio. Figure 5.38 illustrates that 21 December received the minimum
mean work plane illuminance for all overhang tested at reference point 02. Further,
at overhang ratio 1.3 and above, the illuminance level falls below the 500 lux
illuminance level. When overhang ratio of 1.3 (2.3 meter or 7.5 ft) is added to the
depth of the room (6.0 meter or 20 ft) it gives a total depth of 8.3 meter (27.5 ft) to
the back of the room (figure 5.39). Thus, the ratio between the height of the aperture
(1.82 meter or 6 ft, from top of the sill to ceiling) and the depth of the equivalent
room (8.3 meter or 27.5 ft) is about 1: 4.5. In other words, required natural-light
penetrates into the room to a depth of 4.5 times the height of the aperture on the west
orientation.
Mean work plane illuminance (lux)
3000
2500
2000
1500
1000
500
0
0
0.2
0.4
0.6
0.8
1
1.2
1.4
1.6
Overhang ratio
21-Mar
22-Jun
24-Sep
21-Dec
Figure 5.37: Mean work plane illuminance (lux) at reference point 01 for tested
overhang ratio- 21 March, 22 June, 24 September, and 21 December for West
orientation.
212
1750
Mean work illuminance (lux)
1500
1250
1000
750
500
250
0
0
0.2
0.4
0.6
0.8
1
1.2
1.4
1.6
Overhang ratio
21-Mar
22-Jun
24-Sep
21-Dec
Figure 5.38: Mean work plane illuminance (lux) at reference point 02 for tested
overhang ratio- 21 March, 22 June, 24 September, and 21 December for West
orientation
Figure 5.39: Effect of overhangs on natural light distribution in perimeter office
room- West orientation
213
5.2.3 North Orientation
Solar heat gain (W/m2)
Illuminance(lux)
2500
165
2250
150
2000
135
12:00
120
15:00
1750
105
1500
9:00
17:00
90
1250
75
1000
60
750
500
45
30
Target Illuminance
250
15
0
0
0
0.4 0.6 0.8
1
1.4
0
Light Reference Pt. 01
0.4 0.6 0.8
1
1.4
0
0.4 0.6 0.8
1
1.4
Light Reference Pt. 02
Overhang ratio
Figure 5.40: Absolute work plane illuminance (lux) at ref.pt:01, ref.pt:02, and
solar heat gain (W/m2), as a function of overhang ratio- 21 March, North orientation
2
Illuminance(lux)
Solar heat gain (W/m )
2500
240
225
2250
210
195
2000
180
1750
9:00
12:00
15:00
165
150
1500
17:00
135
1250
120
105
1000
90
75
750
Target Illuminance
60
500
45
30
250
15
0
0
0
0.4 0.6 0.8
1
Light Reference Pt. 01
1.4
0
0.4 0.6 0.8
1
1.4
0
0.4 0.6 0.8
1
1.4
Light Reference Pt. 02
Overhang ratio
Figure 5.41: Absolute work plane illuminance (lux) at ref.pt:01, ref.pt:02, and
solar heat gain (W/m2), as a function of overhang ratio- 22 June, North orientation
214
Illuminance(lux)
2
Solar heat gain (W/m )
2250
150
2000
135
9:00
12:00
120
1750
15:00
105
1500
17:00
90
1250
75
1000
60
750
45
500
30
Target Illuminance
250
15
0
0
0
0.4 0.6 0.8
1
1.4
0
Light Reference Pt. 01
0.4 0.6 0.8
1
1.4
0
0.4 0.6 0.8
1
1.4
Light Reference Pt. 02
Overhang ratio
Figure 5.42: Absolute work plane illuminance (lux) at ref.pt:01, ref.pt:02, and
solar heat gain (W/m2), as a function of overhang ratio- 24 September, North
orientation
2
Illuminance(lux)
Solar heat gain (W/m )
135
1750
9:00
120
1500
12:00
105
15:00
1250
90
17:00
1000
75
750
60
45
500
30
250
15
Target Illuminance
0
0
0
0.4 0.6 0.8
1
Light Reference Pt. 01
1.4
0
0.4 0.6 0.8
1
1.4
0
0.4 0.6 0.8
1
1.4
Light Reference Pt. 02
Overhang ratio
Figure 5.43: Absolute work plane illuminance (lux) at ref.pt:01, ref.pt:02, and
solar heat gain (W/m2), as a function of overhang ratio- 21 December, North
orientation
215
Figures 5.40 to 5.43 illustrate that the maximum work plane illuminance are
obtained during 12:00 and 15:00 hours on four correspondence dates, at both
reference points, when the office space is facing towards the north. During the mid
day hours the sun is at higher altitudes and the amount of diffuse sky illuminance is
high. Generally, there were less illuminance in the morning 9:00 and evening 17:00
hours. However, on 21 March and 22 June, illuminance at 9:00 and 17:00 hours
indicated a higher value respectively, similar to illuminance obtained during the mid
day. This can be explained thus on March the north façade do not receive direct
sunlight but the external horizontal illuminances are high at 9:00 than at 17:00 hour.
But on 22 June, the façade receives direct sunlight; therefore the illuminance values
are high (figure 5.41). The illuminance profile also showed a high gradient at
reference point 01 than at reference point 02. This indicates, with the increase of
overhang depth, the illuminance levels were reduced significantly at the center of the
office room than at back of the room compared to base case illuminance values at
respective locations.
Table 5.5 a & b, shows the maximum, minimum and mean illuminance
values at correspondence reference points on all four days, at the north oriented
office room. On 21 March, all overhang ratios indicated minimum work plane
illuminance above 500 lux, at reference point 01. Overhang ratios of 1.0 and 0.8,
indicated minimum illuminance of less than 500 lux at reference point 01 and
reference point 02, on 22 June and 21 March respectively. But on 22 June, all
overhang options indicated the minimum work plane illuminance below 500 lux at
reference point 02 (table 5.5a). Similarly, overhang ratio 1.4 and bare window
indicated less than 500lux for minimum illuminance on 24 September and 21
December respectively at reference point 01 (table 5.5b).
At reference point 02, overhang ratio of 0.4 obtained below 500 lux on 24
September and 21 December (table 5.5b). However, the best minimum illuminance
below 500 lux was indicated at reference point 02 (358 lux) on 21 December for base
case option, on the north orientated office space. On the above date, the main source
of illuminance and solar heat were obtained from external diffuse sky light and
diffuse solar radiation. The correspondence maximum heat gain values of 151
216
W/m2, 223 W/m2, 133 W/m2 and 118 W/m2 were indicated on 21 March, 22 June, 24
September and 21 December respectively, for the base case options in order to
maintain 358 lux illuminance level on 21 December.
Table 5.5a: Maximum, minimum and mean work plane illuminance values at ref.
pt: 01, ref. pt: 02, and total solar heat gain- 21 March and 22 June, North orientation
OHR
(PF)
Total Illuminance (Sunlight & Daylight)(lux) at Reference Pt:01
21-Mar
22-Jun
Maxm % Minm % mean % Maxm % Minm % mean
0
2239
0 1230 0 2046 0
2168
0
879
0 1994
0.4
1554 31 887 28 1473 28 1562 28 642 27 1424
0.6
1477 34 843 31 1401 32 1495 31 609 31 1354
0.8
1242 45 716 42 1177 42 1234 43 506 42 1120
1203 46 694 44 1132 45 1190 45 489 44 1082
1
1.4
1054 53 604 51 971 53
996
54 416 53 913
Total Illuminance (Sunlight & Daylight)(lux) at Reference Pt.02
OHR
21-Mar
22-Jun
(PF)
Maxm % Minm % mean % Maxm % Minm % mean
0
1231
0
724
0 1163 0
1104
0
476
0 1028
0.4
996
19 561 23 936 20
872
21 385 19 816
0.6
936
24 518 29 855 26
802
27 353 26 746
710
36 311 35 656
0.8
867
30 466 36 775 33
1
829
33 445 38 730 37
665
40 294 38 619
1.4
776
37 409 44 673 42
590
47 265 44 550
Total solar heat gain (Transmitted & re-conducted) (W/m2)
OHR
21-Mar
22-Jun
(PF)
0
0.4
0.6
0.8
1
1.4
Maxm
151
121
112
107
103
98
%
0
29
32
44
46
54
%
0
21
27
36
40
47
% Minm % mean % Maxm % Minm % mean %
0
77
0
114
0
223
0
97
0
160
0
60
23
90
21
64
34
89
44
20
114
49
26
54
30
83
27
102
54
53
45
77
52
93
58
45
53
69
57
29
50
35
79
31
31
47
39
75
34
86
61
42
56
64
60
35
43
45
71
38
77
66
38
61
57
64
Comparison of the mean work plane illuminance on respective days indicated
that overhang ratio of 0.4 obtained the best minimum illuminance (459 lux) below
500 lux level at reference point 02 for 21 December (table 5.5b). According to table
5.6a and b, the correspondence maximum heat gains for the above overhang ratio
(0.4) indicated 20%, 49%, 15% and 14% reduction compared to the base case option
on 21 March, 22 June, 24 September and 21 December respectively. Hence, 22 June
217
showed a significant reduction than on other days, which means low overhang ratio
is adequate to obstruct the direct sun penetrating into the office space. Increase of
overhang ratio up to 1.4 reduced the maximum solar heat gain by 35%, 66%, 29%
and 28% respectively on all four days considered. This indicates that the solar heat
gain from the direct sun as well as from the diffuse radiation can be significantly
reduced by the external horizontal overhangs. However, overhang ratio of 1.4
reduced the correspondence minimum work plane illuminance at reference point 02
up to 409 lux, 265 lux, 296 lux and 239 lux on respective days. This is about 18%,
47%, 40.8% and 52% reduction from the target illuminance value (500 lux) at
reference points 02.
Table 5.5b: Maximum, minimum and mean work plane illuminance values at ref.
pt: 01, ref. pt: 02, and total solar heat gain- 24 September and 21 December, North
orientation
OHR
(PF)
Total Illuminance (Sunlight & Daylight)(lux) at Reference Pt:01
24-Sep
21-Dec
0
0.4
0.6
0.8
1
1.4
OHR
(PF)
Maxm % Minm % mean % Maxm % Minm % mean
1987
0 1194 0 1650 0
1490
0
495
0 1139
1386 30 811 32 1189 28 1148 23 388 22 804
1330 33 765 36 1122 32 1106 26 374 24 761
1139 43 617 48 908 45
960
36 340 31 619
1104 44 590 51 867 47
933
37 332 33 592
832
44 310 37 492
971
51 486 59 720 56
Total Illuminance (Sunlight & Daylight)(lux) at Reference Pt.02
24-Sep
21-Dec
%
0
29
33
46
48
57
Maxm
1066
929
873
811
776
730
%
0
17
24
33
37
42
0
0.4
0.6
0.8
1
1.4
OHR
(PF)
0
0.4
0.6
0.8
1
1.4
Maxm
133
113
107
102
99
94
% Minm % mean % Maxm % Minm % mean
0
587
0
890
0
358
0
849
0
551
798
10 308 14 459
13 455 23 679 20
18 409 30 612 28
755
15 294 18 417
24 359 39 540 36
709
20 282 21 370
27 332 43 499 41
681
23 268 25 346
32 296 50 447 47
646
27 239 33 322
Total solar heat gain (Transmitted & re-conducted) (W/m2)
24-Sep
21-Dec
% Minm % mean % Maxm % Minm % mean %
0
82
0
108
0
118
0
52
0
85
0
45
15
73
14
15
61
25
87
19
102
14
20
55
33
81
25
96
19
40
23
68
20
23
50
39
76
29
92
22
37
30
65
24
26
47
43
73
32
90
24
34
34
62
27
86
28
31
41
58
32
29
42
49
68
37
218
5.2.3.1 Window Height to Room Depth Ratio-North Orientation
The mean work plane illuminance at reference point 01 illustrated well above
target illuminance level for all overhang tested (figure 5.44). As the overhang ratio
increases, the mean work plane illuminance were gradually reduced at both reference
points. But on 21 December overhang ratio 0.2 indicated the illuminance value as
500 lux at reference point 02 and further reduced with the increase of the overhang
ratio (figure 5.45).
Mean work plane illuminance (lux)
2250
2000
1750
1500
1250
1000
750
500
250
0
0
0.2
0.4
0.6
0.8
1
1.2
1.4
1.6
Overhang ratio
21-Mar
22-Jun
24-Sep
21-Dec
Figure 5.44: Mean work plane illuminance (lux) at ref. point 01 for tested
overhang ratio- 21 March, 22 June, 24 September, and 21 December for North
orientation
Mean work plane illuminance (lux)
1250
1000
750
500
250
0
0
0.2
0.4
0.6
0.8
1
1.2
1.4
1.6
Overhang ratio
21-Mar
22-Jun
24-Sep
21-Dec
Figure 5.45: Mean work plane illuminance (lux) at ref. point 02 for tested
overhang ratio- 21 March, 22 June, 24 September, and 21 December for North
orientation
219
Hence, when overhang ratio of 0.2 (0.36 meter or 1.2 ft) is added to the depth
of the room (6.0 meter or 20 ft), it gives a total depth of 6.4 meter (21.2 ft) to the
back of the room (figure 5.46). Similar to the west oriented aperture, it can be
assumed that the required natural light is penetrated into the room to depth of 3.5
times, the height of the aperture on the north orientation as well.
Figure 5.46: Effect of overhangs on natural light distribution in perimeter office
room- North orientation
5.2.4 South Orientation
Figures 5.47 to 5.50 show that the maximum work plane illuminance was
obtained during 12:00 hours, for both reference points, when the office space is
facing towards the south, on 21 March, 22 June, 24 September and 21 December.
The illuminance profile at 12:00 and 15:00 hours had a similar pattern at reference
point 01 on 21 March, 22 June and 24 September. An overhang ratio of 1.0 indicated
work plane illuminance below 500 lux level at reference point 02, on 21 March
(figure 5.47). Simultaneously, reference point 01 indicated an illuminance value of
770 lux and maximum solar heat gain 111W/m2 (31% reduction compared to the
base case model) for the correspondence overhang ratio of 1.0. Similarly, overhang
ratios of 0.4, 1.4 and 0.8 obtained illuminance values below 500 lux level at
reference point 01 on 22 June and 24 September, and at reference point 02 on 21
220
December, respectively. The maximum solar heat gain resulted for the above
correspondence overhang ratios showed reduction of 23%, 29% and 73% compared
to the base case model without overhang (Table 5.6a & b).
The profile of the chart indicated a higher gradient with the increase of
overhang ratios. This implies that introduction of overhang had a significant impact
on reducing the illuminance level at first reference point. However, on 21 December
the profile at 12:00 hour showed more curved pattern than on other days. Also, an
introduction of an overhang, reduced the illuminance value by 43% at reference point
01, compared to the base case model (table. 5.6 b). This is mainly due to the
interruption of the direct sunlight penetration into the space.
The illuminance profile at reference point 02 illustrated a low gradient pattern
compared to the reference point 01 on 21 March, 22 June and 24 September
respectively (figure 5.47, 5.48 and 5.49). Hence, illuminance at reference point 02 is
mainly from the diffuse sky illuminance, thus increase of overhang depth had a lesser
effect on the internal illuminance level. However, on 21 December the profile at
reference point 02 showed a curved profile during 12:00 hour compared to other
hours (figure 5.50). This initial high illuminance value (at overhang ratio ‘0’) is due
to the direct sun patch received at the back of the room.
Table 5.6 a & b, show the maximum, minimum and mean illuminance and
solar heat gain values obtained at reference point 01 and 02 for the south oriented
office room. An overhang ratio of 0.4 indicated the minimum work plane
illuminance below 500 lux at reference point 01, while all overhang options showed
work plane illuminance below the target level at reference point 02, on 22 June (table
5.6 a). Compared with other three days, 22 June indicated lower values for minimum
work plane illuminance at reference point 02. According to table 5.6 a & b, overhang
ratio of 1.4 indicated the mean work plane illuminance below 500 lux at reference
point 02 on 22 June and 24 September. Application of overhang ratio 1.4 resulted in
reducing the maximum solar heat gain by 37%, 45%, 29% and 76% compared to the
base case option, on 21 March, 22 June, 24 September and 21 December
respectively. A higher percentage reduction on 21 December is due to the
221
obstruction of direct sunlight penetration into the space. Also, the sun is on the south
solstice and the influence of direct sunlight is higher on the south oriented window
on the above date. However, on 21 March, 22 June and 24 September, influence of
the diffuse radiation is higher than the direct sunlight. Therefore, a lesser percentage
reduction for maximum heat gain was indicated on above dates, on the south oriented
room.
Solar heat gain (W/m2)
Illuminance(lux)
2500
180
2250
165
2000
1750
9:00
150
12:00
135
15:00
120
1500
105
1250
90
1000
75
17:00
60
750
45
500
30
Target Illuminance
250
15
0
0
0
0.4 0.6 0.8
1
1.4
0
Light Reference Pt. 01
0.4 0.6 0.8
1
1.4
0
0.4 0.6 0.8
1
1.4
Light Reference Pt. 02
Overhang ratio
Figure 5.47: Absolute work plane illuminance (lux) at ref.pt:01, ref.pt:02, and
solar heat gain (W/m2), as a function of overhang ratio- 21 March, South orientation
Illuminance(lux)
Solar heat gain (W/m2)
2000
135
1750
120
9:00
1500
1250
12:00
105
15:00
90
17:00
75
1000
60
750
45
Target Illuminance
500
30
250
15
0
0
0
0.4 0.6 0.8
1
Light Reference Pt. 01
1.4
0
0.4 0.6 0.8
1
1.4
0
0.4 0.6 0.8
1
1.4
Light Reference Pt. 02
Overhang ratio
Figure 5.48:
Absolute work plane illuminance (lux) at ref.pt:01, ref.pt:02, and
solar heat gain (W/m2), as a function of overhang ratio- 22 June, South orientation
222
Illuminance(lux)
Solar heat gain (W/m2)
2250
180
2000
160
1750
140
1500
120
1250
100
1000
80
750
60
9:00
12:00
15:00
17:00
500
40
Target Illuminance
250
20
0
0
0
0.4 0.6 0.8
1
1.4
0
Light Reference Pt. 01
0.4 0.6 0.8
1
1.4
0
0.4 0.6 0.8
1
1.4
Light Reference Pt. 02
Overhang ratio
Figure 5.49: Absolute work plane illuminance (lux) at ref.pt:01, ref.pt:02, and
solar heat gain (W/m2), as a function of overhang ratio- 24 September, South
orientation.
Illuminance(lux)
2
Solar heat gain (W/m )
2750
450
2500
420
9:00
390
12:00
2250
360
2000
330
300
1750
17:00
270
1500
240
1250
210
180
1000
750
15:00
150
120
Target Illuminance
90
500
60
250
30
0
0
0
0.4 0.6 0.8
1
Light Reference Pt. 01
1.4
0
0.4 0.6 0.8
1
1.4
0
0.4 0.6 0.8
1
1.4
Light Reference Pt. 02
Overhang ratio
Figure 5.50: Absolute work plane illuminance (lux) at ref.pt:01, ref.pt:02, and
solar heat gain (W/m2), as a function of overhang ratio- 21 December, South
orientation.
223
Table 5.6a: Maximum, minimum and mean work plane illuminance values at ref.
pt: 01, ref. pt: 02, and total solar heat gain- 21 March and 22 June, South orientation
OHR
(PF)
Total Illuminance (Sunlight & Daylight)(lux) at Reference Pt:01
21-Mar
22-Jun
0
0.4
0.6
0.8
1
1.4
OHR
(PF)
Maxm % Minm % mean % Maxm % Minm % mean
2367
0 1347 0 2177 0
1853
0
629
0 1482
1608 32 1001 26 1552 29 1389 25 466 26 1126
1507 36 929 31 1465 33 1332 28 447 29 1082
1256 47 770 43 1223 44 1114 40 369 41 908
1216 49 746 45 1173 46 1078 42 356 43 880
1064 55 642 52 1001 54
912
51 298 53 749
Total Illuminance (Sunlight & Daylight)(lux) at Reference Pt:02
21-Mar
22-Jun
%
0
24
27
39
41
49
Maxm
1347
1035
944
873
833
779
%
0
13
19
28
31
38
0
0.4
0.6
0.8
1
1.4
OHR
(PF)
0
0.4
0.6
0.8
1
1.4
Maxm
162
125
117
111
107
101
% Minm % mean % Maxm % Minm % mean
0
811
0 1278 0
926
0
305
0
751
23 655 19 1009 21
796
14 260 14 653
30 583 28 918 28
738
20 241 21 610
35 507 38 816 36
660
29 213 30 544
623
33 200 34 516
38 482 41 766 40
42 435 46 698 45
557
40 178 42 463
Total solar heat gain (Transmitted & re-conducted) (W/m2)
21-Mar
22-Jun
% Minm % mean % Maxm % Minm % mean %
0
81
0
121
0
115
0
44
0
80
0
22
62
24
93
23
88
23
33
25
61
24
28
56
31
86
29
80
30
30
33
55
31
31
51
37
81
33
74
36
27
39
50
37
69
40
25
43
47
41
34
48
40
78
36
44
46
73
40
23
49
43
46
37
63
45
224
Table 5.6b: Maximum, minimum and mean work plane illuminance values at ref.
pt: 01, ref. pt: 02, and total solar heat gain- 24 September and 21 December, South
orientation
OHR
(PF)
Total Illuminance (Sunlight & Daylight)(lux) at Reference Pt:01
24-Sep
21-Dec
Maxm % Minm % mean % Maxm % Minm % mean
0
2042
0 1238 0 1754 0
2520
0 1268 0 1724
0.4
1398 32 851 31 1243 29 1426 43 922 27 1202
0.6
1341 34 790 36 1166 34 1243 51 862 32 1059
0.8
1147 44 627 49 940 46 1058 58 713 44 873
1
1112 46 599 52 897 49 1007 60 680 46 833
866
66 574 55 727
1.4
976
52 494 60 742 58
Total Illuminance (Sunlight & Daylight)(lux) at Reference Pt:02
OHR
24-Sep
21-Dec
(PF)
Maxm % Minm % mean % Maxm % Minm % mean
0
1189
0
621
0
900
0
1853
0
731
0 1263
0.4
934
21 489 21 724 20 1141 38 601 18 880
0.6
877
26 427 31 647 28
971
48 541 26 731
815
31 366 41 566 37
0.8
848
54 479 34 642
1
778
35 338 46 523 42
811
56 447 39 597
732
38 300 52 464 48
756
59 398 46 535
1.4
Total solar heat gain (Transmitted & re-conducted) (W/m2)
OHR
24-Sep
21-Dec
(PF)
0
0.4
0.6
0.8
1
1.4
Maxm
153
129
122
117
113
108
%
0
30
39
49
52
58
%
0
30
42
49
53
58
% Minm % mean % Maxm % Minm % mean %
0
86
0
119
0
428
0
136
0
282
0
15
64
25
97
19
168
61
95
30 132 53
20
57
33
90
25
123
71
81
41 102 64
23
52
39
85
29
116
73
70
48
93
67
26
49
43
81
32
110
74
63
54
87
69
44
49
76
37
56
59
79
72
29
103
76
5.2.4.1 Window Height to Room Depth Ratio-South Orientation
The mean work plane illuminance at reference point 01 illustrated well above
target illuminance level for all overhang tested and on 22 June received the lowest
illuminance levels (figure 5.51). During this date (22 June) the sun is on the north
solstice, thus diffuse light is received through the south oriented aperture. As the
overhang ratio increases, mean work plane illuminance were gradually reduced at
both reference points.
225
Mean work plane illuminance (lux)
2500
2250
2000
1750
1500
1250
1000
750
500
250
0
0
0.2
0.4
0.6
0.8
1
1.2
1.4
1.6
Overhang ratio
21-Mar
22-Jun
24-Sep
21-Dec
Figure 5.51: Mean work plane illuminance (lux) at ref. point 01 for tested
overhang ratio- 21 March, 22 June, 24 September, and 21 December for South
orientation
Mean work plane illuminance (lux)
1500
1250
1000
750
500
250
0
0
0.2
0.4
0.6
0.8
1
1.2
1.4
1.6
Overhang ratio
21-Mar
22-Jun
24-Sep
21-Dec
Figure 5.52: Mean work plane illuminance (lux) at ref. point 02 for tested
overhang ratio- 21 March, 22 June, 24 September, and 21 December for South
orientation.
On 22 June, overhang ratio of 1.0 indicated the illuminance value as 500 lux
at reference point 02 and further reduced with increase of overhang ratio (figure
5.52). Hence, when overhang ratio of 1.0 (1.82 meter or 6 ft) is added to the depth of
the room (6.0 meter or 20 ft), it gives a total depth of 7.9 meter (26 ft) to the back of
226
the room (figure 5.53). Therefore, the ratio between aperture height and total depth
of the equivalent room is 1: 4.3. Similar to the north oriented aperture, it can be
assumed that the required natural light is penetrated into the room to a depth of 4.3
times as the height of the aperture on south orientated office room.
Figure 5.53: Effect of overhangs on natural light distribution in perimeter office
room- South orientation
5.2.5 Hourly Variation of Work Plane Illuminance
Figure 5.54 to 5.57 show the minimum work plane illuminances obtained for
each hour during the office operation for the east, west, north and south oriented
office room. The minimum level of illuminance at reference point 02 is assumed as
the dullest interior natural light conditions for the chosen shading strategy obtained.
If the minimum illuminance level is inadequate to provide amount of light required
then the artificial lighting will be supplemented.
According to illuminance results on figure 5.54, the peak illuminance were
indicated between 10:00 and 11:00 hours for bare window, on the east oriented office
room. However, overhang ratio of 0.8 and above indicated a shift in the peak
illuminance hour toward 12:00 hour for the correspondence overhangs. Increase of
overhang ratio also reduced the number of hours that are above the 500 lux
227
illuminance level. When maximum overhang was applied (overhang ratio 1.6), only
three hours received above the 500 lux illuminance level. However, overhang ratio
0.6 on the east orientation, maintained the required work plane illuminance for about
seven hours (from 9:00 to 16:00 hour).
Work Plane Illuminance (lux)
1750
1500
1250
1000
750
500
250
0
8
9
10
11
12
13
14
15
16
17
18
Hour
ohr 0
ohr 0.4
ohr 0.6
ohr 0.8
ohr 1.0
ohr 1.4
ohr 1.6
Figure 5.54: Minimum hourly work plane illuminance at ref. pt: 02, East orientation
Work plane illuminance (lux)
1500
1250
1000
750
500
250
0
8
9
10
11
12
13
14
15
16
17
18
Hour
ohr 0
ohr 0.4
ohr 0.6
ohr 0.8
ohr 1.0
ohr 1.4
ohr 1.6
Figure 5.55: Minimum hourly work plane illuminance at ref. pt: 02, West orientation
The peak illuminance level for the west oriented bare window was achieved
between 14:00 and 15:00 hours (figure 5.55). Increase of overhang ratios shift the
228
peak illuminance hour between 12:00 and 14:00 hours. However, during evening
hours on the east and morning hours on the west oriented office rooms may require
artificial lighting as the work plane illuminance fall below the required lighting level.
Overhang ratio of 0.6 on the west orientation can maintain the required work plane
illuminances for about seven hours (from 10:00 to 17:00 hour).
Work plane illuminance (lux)
1000
750
500
250
0
8
9
10
11
12
13
14
15
16
17
18
Hour
ohr 0
ohr 0.4
ohr 0.6
ohr 0.8
ohr 1.0
ohr 1.4
Figure 5.56: Minimum hourly work plane illuminance at ref. pt: 02, North
orientation
Work Plane Illuminance (Lux)
1250
1000
750
500
250
0
8
9
10
11
12
13
14
15
16
17
18
Hour
ohr 0
Figure 5.57:
orientation
ohr 0.4
ohr 0.6
ohr 0.8
ohr 1.0
ohr 1.4
Minimum hourly work plane illuminance at ref. pt: 02, South
229
As shown in figure 5.56 and 5.57, the work plane illuminance profiles are
almost similar, for the north and south orientations. Hence, the peak illuminance
levels are obtained during the noon hours. Increase in overhang ratio reduced the
peak illuminance as well as the number of hours above the target illuminance level
(500 lux). Overhang ratio above 0.6 (0.6, 0.4 & bare window) maintained the
required illuminance level for about six hours, while for overhang ratio of 0.4 and
above (0.4 & bare window) the illuminance was above the target level for seven
hours on the south orientation. In other words, 75% and 87% of working hours
constantly received work plane illuminance more than 500 lux, on north and south
orientations respectively.
5.2.6 External Horizontal Overhang and Work Plane Illuminance
The work plane illuminance at two reference points along the median axis
were evaluated for tested overhang ratios. These two points were positioned in such
away to get a general illuminance at center and at back of the office room
considered. The work plane illuminance values obtained were from three light
sources; the direct sunlight, diffuse sky light and reflected light. The maximum,
minimum and mean values were calculated for better understanding of the
illuminance levels obtained at reference points.
5.2.6.1 Impact of Overhang on Target Illuminance Level (500lux)
The orientations of the window affect significantly on work plane
illuminance levels for different hours during the day. The maximum illuminance
values were received on east in the morning (9:00 & 12:00 hours) and on west in the
evening (15:00 & 17:00 hours) hours respectively. The highest illuminance levels
were indicated at low altitude sun positions for the east and west orientations.
However, north and south orientations received higher illuminances at early noon
and early evening hours (12:00 and 15:00 hours) when the sun is at higher altitudes.
230
Low illuminance values were indicated at early morning hours (9:00 hour) and late
evening hours (17:00 hour) when the sun is furthest from the equator, on the north
and south orientations respectively.
The results also indicated that different days of the year received different
illuminance levels based on the orientation of the window. This is best explained by
the mean work plane illuminance values obtained. According to the results, east
orientation received the maximum illuminance on 21 March at both reference points,
while minimum values were indicated on 21 December at reference point 01 and 21
December and 24 September at reference point 02. The maximum work plane
illuminance values were received on 22 June and 21 March at respective reference
points and minimum illuminance values were received on 21 December and 22 June
through the west window. For north and south orientations, the maximum natural
light occurred on 21 March, whereas 21 December and 22 June received the
minimum amount of illuminance, respectively. Hence, the maximum natural light
was obtained when the sun is over the equator (on 21 March) on all orientations
respectively. On 22 June and 21 December, the sun is at the furthest from the
equator, which resulted in low illuminance values.
Further, mean target illuminance value of 500 lux at reference point two was
achieved by overhang ratio of 1.0, 1.3, 0.2 and 1.0 on east, west, north and south
orientations respectively. Further increase in overhang depth may require artificial
lighting to achieve the target illuminance level. This indicates that in natural light
point of view, deep overhang can be used on the west orientation, while on the north
window the shading depth is limited to very small overhang projections. The impact
of above overhang ratios on the incident and transmitted solar radiations was
illustrated on table 5.7 (see figure 5.19, 5.20 & 5.21). The results indicated over 64%
of heat gain reduction compared to total incident solar radiation on base case option,
for correspondence overhang ratio for east, west and south orientations. The north
orientation has a low reduction percentage on incident solar radiation and heat gains
for the correspondence overhang ratio (OHR 0.2) compared to other orientations.
231
Table 5.7: Reduction percentages of cumulative direct, diffuse and transmitted
solar radiation for optimum overhang ratio for target work plane illuminance level
East
Optimum
OHR for
target work
plane
illuminance
(500 lux)
1.0
West
1.3
76%
44%
Over 65%
North
0.2
52%
12%
Over 40%
South
1.0
85%
38%
Over 64%
Orientation
Reduction %
Direct
incident solar
radiation
Reduction %
Diffuse
incident solar
radiation
Reduction %
transmitted
heat gain
77%
38%
Over 65%
5.2.6.2 Window Height to Room Depth Ratio
The proportional relationship between natural light penetration into the room
and height of the window were derived:
Natural light penetration; East 4.3 time’s height of aperture
West 4.5 times height of aperture
North 3.5 times height of aperture
South 4.3 times height of aperture.
This indicates that natural light can penetrate more than 2.5 times the window
height (which is commonly used by architects and engineers as rule of thumb) in
tropical climate with ample natural light in the sky. However, for a lower target
illuminance of 300 lux, the natural lighting range would be penetrating into deeper
area.
232
5.3 Summary
The results, analysis and findings of the simulation exercise to determine the
influence of the external horizontal shading depth on incident solar radiation,
transmitted heat gains and on work plane illuminance were presented in this chapter.
The analysis of the above performance variables were carried out for the base-case
model and overhang ratios of 0.4, 0.6, 0.8, 1.0, 1.4 and 1.6 for east, west, north and
south orientations (north and south orientations up to OHR 1.4). The results of
direct and diffuse incident solar radiation and transmitted solar heat gains were
plotted against overhang ratio in the same graph. Similarly, work plane illuminance
and solar heat gains were also plotted against overhang ratio in the same graph. It
enabled to understand the influence of overhang depth (given as ratio) on each
component on the correspondence orientations, dates and hours. The hourly
maximum results for transmitted heat gains and hourly minimum work plane
illuminances were also analyzed for the respective orientations. This gave overall
view of the influence of overhang on the patterns of heat and work plane illuminance
variation throughout the day. Table 5.8 illustrates the summary of the findings.
Table 5.8: Summary of optimum overhang ratio for incident solar radiations,
transmitted heat gains and work plane illuminance
Optimum
OHR for
maximum
Orientation reduction
of incident
direct solar
radiation
East
West
North
South
1.2
1.6
0.6
0.8
Optimum
OHR for
maximum
reduction
of incident
diffuse
solar
radiation
1.6
1.6
1.4
1.4
Optimum
Optimum
OHR for
OHR for
maximum
target
reduction
work plane
of
illuminance
transmitted
(500lux)
heat gain
1.6
1.6
1.4
1.4
1.0
1.3
0.2
1.0
CHAPTER 6
RESULTS, ANALYSIS AND FINDINGS:
ENERGY PERFORMANCE
In the previous chapter, section 5.1 specifically evaluates the impact of the
external horizontal solar shading on the direct and diffuse solar radiation incident on
window, and the transmitted heat gains into the building. The results indicated a
significant reduction on solar heat gains into the building when external solar
shading was applied. Section 5.2 discussed the impacts of the external horizontal
solar shading on the internal work plane illuminance and the correspondence solar
heat gains. The results showed that increase in shading device depth reduced the
natural-light penetration in the deep end of the room. Hence, the main drawback of
using shading device in tropical climate is the risk of reducing useful natural-light
into the building, which requires the use of artificial lighting. Further, usages of
artificial lighting consumed more energy as well as contribute to the higher cooling
load. Therefore, it is important to consider both the cooling load and lighting load in
the design of shading device in order to determine an energy efficient shading
system. In this chapter, the simulation results of energy evaluation are discussed in
two sections. Section one, investigates the application of external horizontal solar
shading on office space cooling loads. In section two, the energy consumptions of
the office space are analyzed to determine the influence of correspondence external
overhang devices.
234
6.1 Energy Evaluation
The purpose of the energy consumption evaluation is to investigate the
relationship between the optimum energy use and different horizontal overhang
ratios. The simulation study assesses the effect of the external horizontal shading
device depth configurations on reducing the annual energy consumption for cooling,
lighting and total usage. The energy evaluations are based on the comparison of the
energy performance of the base case model (BC) with no overhang, with naturallight and without natural-light utilization and the respective tested overhang options.
Breakdown of the cooling loads (MWh) for the office space also being considered
based on the each tested external overhang device configuration.
To better understand the electricity consumption due to solar heat gain and
the natural-light, the incremental electricity consumption is correlated with the
external overhang device configurations. The incremental electricity use due to solar
heat gain is the difference between the energy consumption with shading device and
without shading device. Similarly, the incremental electricity consumption due to
natural lighting is determined by the difference between the electricity consumption
with natural-light and consumption without natural-light (see section 3.2.2.4 in
Chapter 3).
The energy evaluation is carried out in two categories:
1. Evaluation of the building components and their contribution into the
building cooling loads.
2. Annual electric consumption for space cooling, artificial lighting and total
usage.
235
6.2. Building Component Cooling Loads
Space cooling load is the rate at which heat must be removed by mechanical
means from the space to maintain the space air temperature at the desired condition.
The simulation results obtained for the generic office room model from the
eQUEST-3, DOE 2.2, are analyzed and discussed in two sections. Section one;
discusses the building cooling load performance of the base case generic office room.
In section two, influence of the external horizontal overhang on the building cooling
loads were analyzed.
6.2.1 Base Case Generic Office Room and Building Component Cooling Loads
Building cooling energy performance of the base case generic office rooms
for the four main cardinal orientations (east, west, north & south) are investigated to
understand the main sources of heat gains and the building parameters of the model.
Figure 6.1 shows the breakdown of the cooling load for the base case generic office
space, with natural-light utilization and without natural-light utilization.
According to figure 6.1 and table 6.1 to 6.4, that 87%, 87%, 83% and 84% of
the building’s total cooling loads are envelop loads and 13%, 13%, 17% and 16% are
internal loads for the base case generic office room with natural-light utilization, for
east, west, north and south orientations respectively. Further, as expected the west
(8.02 MWh) and east (7.99 MWh) orientation had the maximum contribution and
north (6.26 MWh) had the least contribution on the cooling loads.
The solar heat gain and conduction heat gain through the window are the
largest components of the building envelope cooling loads. The base-case cooling
loads due to window conduction and solar radiation had similar contribution of 22%
and 57%, on the east and west orientations, while 27% and 48%, 26% and 50% on
the north and south orientations respectively, compared to the base-case total
building cooling loads. The loads due to conduction through the exterior and internal
236
wall, had little impact on the total cooling loads than the solar radiation through the
2.0
2.0
1.5
1.5
1.0
1.0
0.5
0.5
0.0
0.0
With Natural-light
Cooling Load (MWh)
2.5
Equipment
2.5
Internal
Lighting
3.0
Occupant
3.0
Window
conduction
Window
Sol.radiation
3.5
Infiltration
3.5
Wall
Conduction
4.0
Equipment
4.0
Internal
Lighting
4.5
Occupant
4.5
Window
conduction
Window
Sol.radiation
5.0
Infiltration
5.0
Wall
Conduction
Cooling Load (MWh)
window on the four orientations.
Without Natural-light
Building Components
East
West
North
South
Figure 6.1: Breakdown of annual cooling load (MWh) with natural-light
utilization and without natural-light for a base-case generic office room- East, West,
North and South orientations
The cooling loads from the equipment had the maximum impact on the
internal cooling loads. However, the equipment and number of occupants were kept
constant in the simulation study; therefore their contribution remains the same for all
orientations and for the tested overhang ratios. But impact from internal lighting
changed with the office room orientation and introduction of the horizontal shading
devices. Hence, base-case internal lighting loads contributed annually, 0.29 MWh on
the east, and 0.31 MWh on other three orientations respectively. This means
utilization of natural-light minimize the internal lighting cooling loads. When
natural-light is not utilized, annually 1.44 MWh cooling load is required to remove
the heat gain from internal lighting, in the office room considered (figure 6.1). This
increased the total building cooling and internal loads by 14% on the east and west
orientations, while 18% and 17% on the north and south orientations compared to the
base-case with natural-light total cooling load respectively. In other words, natural-
237
light utilization reduces the cooling load by 14% on both east & west, 18% and 17%
on the north and south orientations respectively. However, the envelop loads
remains the same for without natural-light scheme, hence, utilizing natural-light in
the building reduced the internal loads considerably. Also heat gain from internal
lighting is very low compared to the solar heat gain as the office room considered is
within the 6 meter deep perimeter zone. Therefore the use of artificial lighting is less
due to the natural-light availability.
Analysis of the simulation results of the base case generic office room
indicated that limiting the excessive solar heat gain is the crucial factor while use of
beneficial natural-light as an important energy saving potential in hot and humid
tropical climates. The analysis also indicated that the orientation of the building has a
significant impact on the building cooling load, where the west and east resulted in
high cooling load consumption than, south and north orientations. The north
orientation had the lowest impact on total cooling load. When compared with west
orientation, the total cooling load on north and south orientations showed 22% and
17% reduction respectively. Therefore, based on the above cooling load analysis, it
can be concluded that for location latitude 3.10 north and longitude 101.70 east, the
worst heat gains were obtained from the west and east orientations.
6.2.2 Influence of External Horizontal Overhang on Building Component
Cooling Loads
Table 6.1 to 6.4 show the break down of each building component with
respect to different overhang ratios and their impact on building cooling loads for
east, west, north and south orientations respectively. The building cooling loads
were classified and discussed in two categories based on the sources of heat gain into
the building; envelope and internal cooling loads. The comparison of the building
envelope, internal cooling loads and total cooling loads were made with the basecase generic office room, with natural-light and without natural-light utilization.
238
Introduction of horizontal overhang and increase of overhang ratio from 0.4
to 1.6 (east & west) and 1.4 (north & south) indicated 37%, 33%, 23% and 26%
reduction in the total building cooling loads compared to the base-case model, on
east, west, north and south orientations respectively (table 6.1 to 6.4). The total
building envelop load reduced by 45.0%, 40.4%, 30.3% and 33.6% and total internal
loads increased by 14.3%, 17.5%, 14.6% and 14.3% compared to the base-case loads
on east, west, north and south orientations respectively. The solar heat gain through
the window, when maximum overhang ratio is applied indicated 64.0%, 59.0%,
51.0% and 54.0% reduction on the east, west, north and south orientations
respectively. The internal lighting loads showed 47.2%, 52.7%, 49.3% and 47.9%
increment, compared to the base-case cooling loads on main cardinal orientations
respectively (table 6.1 to 6.4). Although cooling load from window solar heat gains
resulted in significant reduction, cooling load from window conduction indicated
only 7.0%, 3.5%, 1.2% and 2.7% reduction compared to the base-case cooling load,
when the maximum overhang ratio is applied on respective orientations.
Table 6.1: Annual cooling load (MWh) with natural-light utilization and reduction
percentage values as compared to base-case model, for tested OHR-East orientation
Internal load
(MWh)
Envelop load
(MWh)
Overhang ratio
Wall conduction
%
Infiltration
Window conduction
%
Window solar radiation
%
Total Load
%
Occupants
Internal lighting
%
Equipment
Total Load
%
Total building load(MWh)
%
0
0.4
0.6
0.8
1
1.4
1.6
0.37
0.35
0.34
0.33
0.33
0.31
0.31
0.0
5.2
7.7
9.8
11.6
14.7
15.8
0.21
0.21
0.21
0.21
0.21
0.21
0.21
1.80
1.73
1.71
1.70
1.69
1.68
1.67
0.0
3.7
4.8
5.6
6.1
6.9
7.0
4.59
3.17
2.70
2.33
2.09
1.75
1.64
0.0
31.0
41.0
49.0
54.0
62.0
64.0
6.96
5.46
4.96
4.57
4.32
3.94
3.83
0.0
21.6
28.7
34.3
38.0
43.4
45.0
0.14
0.14
0.14
0.14
0.14
0.14
0.14
0.29
0.32
0.34
0.36
0.38
0.42
0.44
0.0
10.2
14.4
23.4
28.6
42.0
47.2
0.60
0.60
0.60
0.60
0.60
0.60
0.60
1.03
1.06
1.07
1.10
1.12
1.16
1.18
0.0
2.9
4.1
6.6
8.1
12.0
14.3
7.99
6.52
6.03
5.67
5.43
5.10
5.01
0.0
18.0
25.0
29.0
32.0
36.0
37.0
239
Table 6.2: Annual cooling load (MWh) with natural-light utilization and reduction
percentage values as compared to base-case model, for tested OHR-West orientation
Internal load
(MWh)
Envelop load
(MWh)
Overhang ratio
Wall conduction
%
Infiltration
Window conduction
%
Window solar radiation
%
Total Load
%
Occupants
Internal lighting
%
Equipment
Total Load
%
Total building load(MWh)
%
0
0.4
0.6
0.8
1
1.4
1.6
0.36
0.35
0.34
0.33
0.32
0.32
0.32
0.0
4.8
6.9
8.9
10.6
13.2
12.6
0.21
0.21
0.21
0.21
0.21
0.21
0.21
1.80
1.74
1.73
1.72
1.71
1.70
1.73
0.0
3.0
3.9
4.5
4.9
5.4
3.5
4.60
3.27
2.82
2.51
2.27
1.96
1.90
0.0
29.0
39.0
46.0
51.0
57.0
59.0
6.97
5.57
5.10
4.76
4.51
4.18
4.16
0.0
20.1
26.9
31.7
35.4
40.0
40.4
0.14
0.14
0.14
0.14
0.14
0.14
0.14
0.31
0.35
0.36
0.39
0.41
0.45
0.48
0.0
10.3
14.8
24.1
29.1
41.9
52.7
0.60
0.60
0.60
0.60
0.60
0.60
0.62
1.05
1.09
1.10
1.13
1.15
1.19
1.24
0.0
3.1
4.4
7.2
8.7
12.5
17.5
8.02
6.65
6.20
5.89
5.65
5.37
5.39
0.0
17.0
23.0
27.0
30.0
33.0
33.0
Influence of heat gain through the window conduction varies with the
increase of overhang ratio. Even though the impact of the window conduction is less
effective compared to the solar radiation heat gains, accumulation of conduction heat
on to the overall building envelope cooling load may affect on large cooling load
energy consumption. It is interesting to note that beyond overhang ratio of 1.4 on
east and west, 1.0 on north and 0.6 on south orientation, the window conduction
cooling load remained at constant value (table 6.1 to 6.4). This was mainly due to
the increase of heat trapped between the horizontal overhang and the window pane.
Hence, the horizontal shading device is effective in terminating the solar radiation
than controlling the conduction heat gains. Therefore, the trapped heat need to be
removed to reduced the conduction cooling load. This implies that introduction of a
gap between the overhang and the wall surface may create room for the heated air to
be released and reduce the surface temperature on the glazing façade.
240
Internal load
(MWh)
Envelop load
(MWh)
Table 6.3: Annual cooling load (MWh) with natural-light utilization and reduction
percentage values as compared to base-case model, for tested OHR-North orientation
Overhang ratio
Wall conduction
%
Infiltration
Window conduction
%
Window solar radiation
%
Total Load
%
Occupants
Internal lighting
%
Equipment
Total Load
%
Total building load(MWh)
%
0
0.4
0.6
0.8
1
1.4
0.31
0.29
0.29
0.28
0.28
0.28
0.0
5.4
7.7
8.8
9.3
10.2
0.21
0.21
0.21
0.21
0.21
0.21
1.68
1.64
1.65
1.65
1.66
1.66
0.0
2.2
2.0
1.8
1.6
1.2
3.01
2.02
1.82
1.69
1.60
1.48
0.0
33.0
39.0
44.0
47.0
51.0
5.21
4.16
3.96
3.84
3.75
3.63
0.0
20.0
23.9
26.3
28.0
30.3
0.14
0.14
0.14
0.14
0.14
0.14
0.31
0.36
0.37
0.41
0.43
0.46
0.0
14.2
20.2
31.4
37.1
49.3
0.60
0.60
0.60
0.60
0.60
0.60
1.05
1.09
1.11
1.15
1.17
1.20
0.0
4.2
6.0
9.3
11.0
14.6
6.26
5.26
5.08
4.98
4.91
4.83
0.0
16.0
19.0
20.0
21.0
23.0
Table 6.4: Annual cooling load (MWh) with natural-light utilization and reduction
percentage values as compared to base-case model, for tested OHR-South orientation
Internal load
(MWh)
Envelop load
(MWh)
Overhang ratio
Wall conduction
%
Infiltration
Window conduction
%
Window solar radiation
%
Total Load
%
Occupants
Internal lighting
%
Equipment
Total Load
%
Total building load(MWh)
%
0
0.4
0.6
0.8
1
1.4
0.32
0.31
0.30
0.29
0.29
0.29
0.0
5.1
7.8
9.7
10.6
11.7
0.21
0.21
0.21
0.21
0.21
0.21
1.72
1.67
1.66
1.66
1.66
1.67
0.0
2.9
3.3
3.1
3.0
2.7
3.35
2.22
1.94
1.78
1.68
1.55
0.0
34.0
42.0
47.0
50.0
54.0
5.59
4.40
4.10
3.95
3.85
3.71
0.0
21.4
26.7
29.5
31.3
33.6
0.14
0.14
0.14
0.14
0.14
0.14
0.31
0.35
0.37
0.41
0.42
0.46
0.0
12.3
18.2
29.5
35.0
47.9
0.60
0.60
0.60
0.60
0.60
0.60
1.05
1.09
1.11
1.14
1.16
1.20
0.0
3.7
5.4
8.8
10.4
14.3
6.65
5.49
5.21
5.09
5.01
4.91
0.0
17.0
22.0
23.0
25.0
26.0
241
The results indicated all orientations had significant reduction on building
envelop cooling loads when solar shadings are applied (figure 6.2). However, the
horizontal shading devices were effective on the east and west orientations which
reduced more than half of the cooling loads, compared to the base-case model
without solar shading. Hence, eliminating the direct solar radiation before reaching
the window pane is the crucial factor in reducing the cooling loads. Although
introduction of external overhang had little impact on internal lighting cooling loads,
increment of overhang ratio increased the amount of heat generated by artificial
lighting that needed to be removed from the space to maintain a constant air
8.0
1.25
7.0
1.20
6.0
1.15
5.0
1.10
4.0
1.05
3.0
Internal cooling load (MWh)
Envelop cooling loads (MWh)
temperature.
1.00
0
0.2
0.4
East env ld
East int ld
0.6
0.8
1
Overhang ratio
West env ld
West int ld
1.2
North env ld
North int ld
1.4
1.6
1.8
South env ld
South int ld
Figure 6.2: Total envelop and internal component cooling loads (MWh) for tested
external horizontal overhang ratio, East, West, North and South orientations
The results indicated little reduction in overall envelope cooling loads for
overhang ratio beyond 1.4 on the east and west orientations. Similar pattern were
obtained for overhang ratio beyond 1.0 for the north and south orientations. Further,
similar results were shown for overall total cooling load (figure 6.3). The maximum
total cooling load reductions on the east and west orientations were obtained for
overhang ratio of 1.4 and overhang ratio of 1.0 for the north and south orientations.
Comparison of cooling loads for each orientation showed that the west orientation
indicated higher envelope and total cooling load than other orientations. The east
242
orientation also showed high cooling load compared to the south and north
orientations, while north had the lowest for both envelope and total cooling loads
(table 6.5). The results thus suggested that overhang ratios of 1.4 on the east and
west; overhang ratio of 1.0 on the north and south orientations can be recommended
for maximum reduction of total heat gain from transmitted and re-conducted solar
radiation into the building. Further, above overhang ratios indicated more than 60%
reductions in total transmittance heat gains for the above stated overhang ratios on
respective orientations (see figure 5.21 in Chapter 5).
8.5
Total Cooling Load (MWh)
8.0
7.5
7.0
6.5
6.0
5.5
5.0
4.5
4.0
0
0.2
0.4
0.6
0.8
1
1.2
1.4
1.6
1.8
Overhang ratio
East
West
North
South
Figure 6.3: Total building space cooling load (MWh) for tested external
horizontal overhang ratio, East, West, North and South orientations
Table 6.5: Summary of building cooling loads and reduction percentages for
optimum overhang ratio compared to base-case model, East, West, North and South
orientations
Orientation
East
West
North
South
Optimum Building envelope
overhang
cooling load &
ratio
reduction %
1.4
3.94 MWh (43.4%)
1.4
4.18 MWh (40.0%)
1.0
3.75 MWh (28.0%)
1.0
3.85 MWh (31.0%)
Internal cooling
load & reduction
%
1.16 MWh (12.0%)
1.19 MWh (12.5%)
1.17 MWh (11.0%)
1.16 MWh (10.4%)
Total cooling load
& reduction %
5.1 MWh (36.0%)
5.37 MWh (33.0%)
4.91 MWh (21.0%)
5.01 MWh (25.0%)
As discussed in chapter 5, the optimum overhang ratio for target illuminance
(500 lux) is 1.0, 1.3, 0.2 and 1.0 on the east, west, north and south orientations
243
respectively. If these overhang ratios were increased to reduce the overall cooling
loads, effect of the lighting cooling load due to required electricity lighting were
negligible compared to the reduction of envelope cooling loads.
Figure 6.4 illustrates the comparison of cooling loads between two extreme
options; the base-case without overhang and maximum overhang, when the natural
light is not utilized to illuminate the space. Application of the maximum overhang
ratios (1.6-east and west; 1.4-north and south) reduced the solar radiation from
window up to 1.64 MWh, 1.86 MWh, 1.48 MWh, and 1.55 MWh, on respective
orientations. The above results indicated 64.0%, 60.0%, 50.0% and 54.0% reduction
compared with the natural-light base-case option, for the east, west, north and south
orientations respectively. However, the conduction heat gain and lighting heat gain
had a lesser impact. This implies even though natural-light is not utilized as energy
efficient measure in buildings, use of the external shading device still can
Without Natural-light and Without
Overhang
Cooling Load (MWh)
Equipment
Internal
Lighting
Occupant
Window
conduction
Window
Sol.radiation
Infiltration
Wall
Conduction
Equipment
Internal
Lighting
Occupant
Window
conduction
Window
Sol.radiation
5,0
4,5
4,0
3,5
3,0
2,5
2,0
1,5
1,0
0,5
0,0
Infiltration
5,0
4,5
4,0
3,5
3,0
2,5
2,0
1,5
1,0
0,5
0,0
Wall
Conduction
Cooling Load (MWh)
significantly reduce the cooling loads.
Without Natural-light and with
Maximum Overhang
Building Components
East
West
North
South
Figure 6.4: Breakdown of annual cooling load (MWh) without natural-light
utilization; for base-case model and maximum overhang option, East, West, North
and South orientations
244
Figure 6.5 and Table 6.6 indicates that shading with natural-light utilization
obtained lowest cooling loads, while without both; natural-light and shading device
obtained the maximum cooling load, for all orientations. The cooling load reduction
percentages are calculated compared to the base-case office room option with
natural-light utilization. Positive values indicated savings and the negative value
indicated loses in cooling loads. The maximum shading with natural light utilization
reduced the total cooling load by 37%, 33%, 23% and 26% compared to the base
case (with natural-light) option on the east, west, north and south orientations
respectively. East and west orientations had the maximum reduction percentage
values as the application of maximum overhang cut-off the direct solar radiation
penetration into the space considered. The north orientation indicated the lowest
reduction percentage value as the increment of overhang depth had little effect on the
diffuse component of solar radiation which is the main source of heat gain through
the north fenestration.
10.0
Total Cooling Load (MWh)
9.0
8.0
7.0
6.0
5.0
4.0
3.0
2.0
1.0
0.0
No Overhang (Base-case)
Maximum Overhang
No Overhang
With Natural-light
Maximum Overhang
Without Natural-light
Overhang Variable
East
West
North
South
Figure 6.5: The annual total cooling load (MWh) with and without natural-light
utilization for base-case model and maximum overhang option, East, West, North
and South orientations
According to table 6.6, when the room was not shaded from solar radiation
and natural-light was not utilized for interior illuminance, the total cooling load
increase by 14% on the east and west, 18% and 17% on the north and south
compared to the base-case with natural-light scheme. In other words, natural-light
245
utilization reduces the total cooling load by 14% on both east and west, 18% and
17% on the north and south orientations respectively. The correspondence office
room with maximum shading and without natural light utilization reduced the total
cooling load by only 25%, 22%, 7% and 11% on east, west, north and south
orientations respectively. Therefore this indicates that in order to obtain maximum
cooling load savings, both natural-light and overhang shading need to be applied on
respective orientations. Total climate rejection building option, without natural-light
and external shading consumed more energy than the base-case option.
Table 6.6: The annual total cooling load (MWh) with and without natural-light
utilization for base-case model and maximum overhang option, East, West, North
and South orientations
With Natural-light
East
West
North
South
Without Natural-light
No
Overhang
(MWh)
Maximum
Overhang
(MWh)
Reduction
%
No
Overhang
(MWh)
Reduction
%
Maximum
Overhang
(MWh)
Reduction
%
7.99
8.02
6.26
6.65
5.01
5.39
4.83
4.91
37
33
23
26
9.135
9.146
7.382
7.770
-14
-14
-18
-17
6.01
6.25
5.80
5.89
25
22
7
11
6.3 Electricity Consumption
The energy analysis of the simulation results are investigated in-terms of
annual electricity consumption under two sections. First section, discusses the annual
electricity consumption of the base case generic office room. In section two, the
influence of the external horizontal overhang on annual electricity consumption were
analyzed and discussed.
6.3.1 Annual Electricity Consumption- Base Case
Figure 6.6 shows the annual electricity consumption for the base-case generic
office room obtained on east, west, north and south orientations under tropical
246
climate conditions. Four components, namely, space cooling, area lighting,
miscellaneous equipment and ventilation fans contributed to the total office room
electricity consumption. In this study miscellaneous equipment and ventilation fans
are set to a constant value for all the shading devices tested. However, it can be seen
that energy use related to the HVAC system (for space cooling and ventilation fans)
dominated the electricity consumption on all four orientations. The east and west
orientations had the highest effect (55.1% & 54.4%) while north and south (49.7% &
50.7%) had the least effect on electricity consumption for space cooling of total
energy use. As expected, under tropical climate with ample natural-light, relatively
electricity consumed for area lighting is insignificant, which accounted only 7.5%,
8%, 8.8% and 8.6% of the total energy use on east, west, north and south orientations
80
60
70
60
50
50
40
40
30
30
20
20
10
10
0
2
70
Annual electricity consumption (kWh/m , yr)
2
Annual electricity consumption (kWh/m , yr)
respectively (table 6.7).
0
Space
Cool
Vent.
Fans
Misc.
Equip.
Area
Lights
With Natural-light utilization
East
West
Space
Cool
Vent.
Fans
Misc.
Equip.
Area
Lights
Without Natural-light utilization
North
South
Figure 6.6: Breakdown of annual electricity consumption for base case model,
with and without natural-light utilization- East, West, North and South orientations
The computed results without natural-light utilization showed significant
increments in electricity consumption for area lighting accounting, 27% on the east
and west orientations while 29% on the north and south orientations, of the total
energy use respectively. Hence, the results indicated the importance of natural-light
utilization and impact of solar heat gains in cooling dominated office room. But the
space cooling energy consumption without natural light utilization indicated higher
247
values compared with natural-light scheme (table 6.7). Increment of the space
cooling loads without natural-light utilization is about 13.2%, 13.1%, 16.7% and
15.7% compared with natural-light scheme on respective orientations. This indicates
that, when natural lighting is not utilized the orientation of the office room has less
impact on the energy consumption for space cooling.
Total Energy Consumption (kWh/m2)
180
Malaysian Energy Standard for
non residential building (135 kWh/m 2 )
165
150
135
120
105
90
75
60
45
30
15
0
East
West
Orientation
With Natural-light
North
South
Without Natural-light
Figure 6.7: Total energy consumption with and without natural-light scheme for
base case model, East, West, North and South orientations
Table 6.7: The annual electricity consumption for base case model, with and
without natural-light utilization, East, West, North and South orientations
Orientation
East
West
North
South
Electricity Energy consumption
Base-case Generic office Room (kWh/m2)
With Natural-light
Total Energy
Space
Area
%
Use
Cooling
lighting
116.0
115.6
104.6
107.0
Total Energy
Use
East
West
North
South
158.2
156.9
146.5
148.6
63.9
62.8
52.0
54.3
55.1
54.4
49.7
50.7
8.6
9.3
9.2
9.2
Without Natural-light
Space
Area
%
Cooling
lighting
72.4
71.1
60.6
62.8
45.7
45.3
41.4
42.2
42.3
42.3
42.3
42.3
%
7.5
8.0
8.8
8.6
%
26.8
27.0
28.9
28.5
248
As illustrated in table 6.7, total energy consumption with natural-light scheme
yielded, below the Malaysian energy standard (135 kWh/m2) for non-residential
buildings (figure 6.7). The results indicated 14% reduction on east and west, 22%
reduction on north and 21% reduction on south oriented office rooms. But total
climate rejecting design option without shading and natural-light utilization, yielded
17%, 16%, 8.5% and 10% more than the energy standards, on the east, west, north
and south orientations respectively.
6.3.1.1 Influence of Orientation on Annual Electricity Consumption- Base Case
The annual building electricity consumption was obtained for four
components, namely; space cooling, ventilation fans, miscellaneous equipment and
area lighting. The results indicated that energy use related to the HVAC system are
the most important components (space cooling and vent fan) in all four orientations
considered. Electricity consumption for area lighting had the least energy usage in a
perimeter generic office room with natural-light utilization. The principle findings
are as follows:
a)
Base-case Generic Office Room: Total Electricity Consumption
The results are obtained for two lighting schemes; with natural-light
utilization and without natural-light utilization for better understanding of the effects
of the natural-light and solar heat gain in the building energy consumption. The
results showed that the designated generic office room energy consumption with
natural-light use for interior illuminance maintained well below the Malaysian
Standard. However, the total energy consumption for climate rejecting office room,
without natural-light and shading option resulted in high electricity consumptions.
The comparison of results between with and without natural-light options showed
that without natural-lighting, the total energy use significantly increased by 36% on
the east and west, 40% on north and 39% on south orientations respectively. Effects
of orientation on the total energy use with natural light were also investigated and the
results were as follows;
249
i. East and west had almost similar amount of energy consumption
ii. North indicated 10% reduction compared to east and west orientations
iii. South indicated 8% reduction compared to east and west orientations
b)
Base-case Generic Office Room: Electricity Consumption for Space
Cooling
Comparison of space cooling energy consumption for different orientation
showed that the east and west orientations consumed more energy than the north and
south orientations. The following illustrates the percentage difference of space
cooling energy consumption between different orientations:
i. West orientation is 1.7% less than east orientation
ii. North orientation is 19% less than east orientation
iii. South orientation is 15% less than east orientation
iv. North orientation is 17% less than west orientation
v. South orientation is 14% less than west orientation
vi. North Orientation is 4% less than south orientation
As indicated above, energy consumption for space cooling on the east
orientation was little higher than the west orientation. This is due to the start-up load
of the HVAC system that required removing the unwanted heat at initial hour of the
day, where the solar heat gain is high on the east oriented office room during
morning hours. When natural-light is not utilized the energy consumption for space
cooling increased by 13% on the east and west orientation, 17% on the north
orientation and 16% on the south orientation (table 6.8). Almost the same results
were obtained for lighting cooling load, when compared to, with and without naturallight utilization options for the base-case model. Therefore, it can be argued that
increment in cooling energy consumption is due to the impact of heat gain from the
artificial lighting into the space.
250
Table 6.8: Summary of impact of artificial lighting on space cooling energy
consumption for base-case model, East, West, North and South orientations
Electricity Use for Space Cooling
(kWh/m2) Base-case generic office room
Orientation
East
West
North
South
With natural-light
utilization
Without naturallight utilization
63.897297
62.818919
51.972973
54.254054
72.351351
71.064865
60.635135
62.762162
Increment
percentage (%)
compared to basecase with naturallight scheme
13%
13%
17%
16%
c)
Base-case Generic Office Room: Electricity Consumption for Area
Lighting
The maximum electricity consumption for area lighting, without natural-light
utilization revealed 27% on the east and west orientation, while 29 % on the north
and south orientation, compared to the total energy consumption of the base-case
model (see table 6.7). These figures indicated that high energy consumption for
lighting in buildings occurs when benefit of natural-light is not taken into
consideration.
The effect of natural-light on energy consumption was compared with
artificially lit generic office room. The use of natural-light reduced the lighting
energy consumption by 80% on the east orientation, and 78% on the west, north and
south orientations respectively. However, in perimeter office room, the orientation
of the window façade has little effect on energy consumption for lighting.
6.3.2 External Horizontal Overhang and Annual Electricity Consumption
Effects of the horizontal overhang depths on annual energy consumptions for
space cooling, area lighting and on total energy consumption are investigated using
the e-QUEST-3 dynamic energy simulation program. Incremental energy
consumptions are calculated and compared with the base-case office room energy
consumption to determine the energy consumption by different shading options.
251
Figure 6.8 (a), (b), (c) and (d) illustrate the annual electricity consumption for space
cooling, area lighting and the total (cooling + lighting) of the generic office room for
different overhang ratios’ tested on the east, west, north and south orientations
respectively.
Electricity Consumption (kWh/m2,yr)
130
120
110
100
90
80
70
60
50
40
30
20
10
0
0
0.2
0.4
0.6
0.8
1
1.2
1.4
1.6
Overhang ratio
cooling
lighting
total
a) East orientation.
Electricity Consumption (kWh/m2,yr)
130
120
110
100
90
80
70
60
50
40
30
20
10
0
0
0.2
0.4
0.6
0.8
1
1.2
1.4
1.6
Overhang ratio
cooling
lighting
total
b) West Orientation
Figure 6.8 (a & b): Electricity consumption (kWh/m2, yr) for space cooling, area
lighting and total energy for tested overhang ratios, East & West orientations.
Electricity Consumption (kWh/m2,yr)
252
110
100
90
80
70
60
50
40
30
20
10
0
0
0.2
0.4
0.6
0.8
1
1.2
1.4
1.6
Overhang ratio
cooling
lighting
total
c) North Orientation
Electricity Consumption (kWh/m2,yr)
120
110
100
90
80
70
60
50
40
30
20
10
0
0
0.2
0.4
0.6
0.8
1
1.2
1.4
1.6
Overhang ratio
cooling
lighting
total
d) South Orientation
Figure 6.8 (c & d): Electricity consumption (kWh/m2, yr) for space cooling, area
lighting and total energy for tested overhang ratios, North & South orientations
The energy consumption for space cooling exhibited inverse curve profile,
while a linear relationship can be observed between the overhang ratio and energy
use for artificial lighting on all orientations (figures 6.8: a, b, c, d). According to the
figures 6.8 (a, b, c, d), increase in overhang ratio resulted in use of artificial lights.
253
The electricity use for space cooling is reduced with the increase of overhang ratio
on all orientations. In other words, the amount of solar heat gains from direct
sunlight and daylight penetration is reduced by the external horizontal shading
devices. The profile for total energy consumption showed an inverse curve with the
increase of overhang ratio on all four orientations. As the overhang ratio increases,
the total energy consumption reduced gradually and at overhang ratio of 1.0, 1.2, and
0.6 the curve showed diminishing return, on east, west and north /south orientations
respectively. Hence, this indicates that optimum energy use can be achieved by
Space cooling consumption (lighting)
14
65
12
60
10
55
8
50
6
45
4
40
35
2
70
2
Electricity consumption(kWh/m ,yr)
Total Space cooling
Electricity consumption(kWh/m ,yr)
control of overhang ratio or else by the shading depth.
2
0
0.4
0.6
0.8
1
1.4
1.6
Overhang ratio
East CL
East(Lt cooling))
West CL
West(Lt cooling)
North CL
North(Lt cooling)
south CL
South(Lt cooling)
Figure 6.9: Total annual electricity consumption for space cooling and annual
electricity consumption for cooling to remove the heat gain from artificial lighting
for different overhang ratio tested- East, West, North and South orientations
Figure 6.9 illustrates the electricity consumed for space cooling. Further, with
the increment of overhang ratio, the heat gain from artificial lighting increased, while
total cooling energy consumption decreased. Initially, at the base case option, over 8
kWh/m2,yr energy is consumed to remove the lighting heat, which is about 13% (east
& west) and 16% (north & south) compared to the total space cooling energy
consumption. This is not surprising, since amount of artificial lighting is being used
to replace the reducing natural-light level. Increasing the overhang ratio from 0 to
254
1.6 and 1.4 on the east/west and north/south orientations indicated almost 13kWh/m2,
yr of the cooling energy was consumed to remove the lighting heat gains. The above
amount is about 30% of cooling energy compared to the total cooling energy
consumption for the same overhang ratios.
The total energy consumption exhibited an inverse curved profile with the
increase of the overhang ratio. Introduction of the external horizontal shading
devices indicated a reduction in total energy use. However, increase of overhang
ratio for maximum reduction of direct solar radiation penetration through the
window, resulted in increasing the total energy consumption. This was evident in
figure 6.8 a, b, c, & d, where increase in overhang ratio from 1.0 to 1.6 on the east
and west orientations, from 0.8 to 1.4 on the north and south orientations, resulted in
an increment of the total energy consumption.
6.3.2.1 Incremental Electricity Use
The incremental energy use (IEU) was correlated with shading overhang ratio
for better understand of the optimum energy consumption due to solar heat gains and
natural-light utilization. In this case the IEU of an externally shaded office room is
calculated compared to the electricity consumed by the base-case generic office room
without an external shading device. Figure 6.10 a, b, c, & d illustrate the correlation
between the incremental energy use (kWh/m2, yr) for space cooling, area lighting
and total energy, with overhang ratios. Trend analysis techniques were used to
confirm the effects of overhang ratio on building energy performance. The technique
was used to build up regression equations correlating the dependent variable with
independent variables. A positive value means more energy is consumed with
shading office room compared to base case generic office room and vice versa.
The incremental electricity use for area lighting (IEU Lt) displayed a linear
relationship with increase of overhang ratio (OHR), on all four orientations. This can
be explained as artificial lighting is significantly displaced by the natural-light. This
255
is expectable as in the tropics there is ample natural-light and for a perimeter zone
office room the required natural-light levels can be easily acquired. Therefore less
electricity is consumed for artificial lighting. However, as the overhang ratio
increases, the capacity of natural-light to replace artificial lighting was reduced
gradually. The correlation between incremental electricity use for space cooling
(IEU CL) and total electricity use (IEU Tot) with overhang ratio (OHR) indicated a
deeper curve profile compared to incremental electricity use for lighting (IEU Lt).
This implies that the external horizontal shading device has significant impact on
space cooling load and the total energy use.
Initial introduction of overhang ratio of 0.4 (overhang depth 0.73meter)
increased the electricity consumption for lighting by 0.9 kWh/m2, yr (10%), 1.0
kWh/m2, yr (10%), 1.3 kWh/m2, yr (14%) and 1.1 kWh/m2, yr (12%) on east, west,
north and south orientations respectively. At the same time, it also reduced the
incremental electricity use for cooling by 10 kWh/m2, yr (16%); 8.9 kWh/m2,yr
(14%); 6.8 kWh/m2, yr (13%) and 7.8 kWh/m2, yr (14%) on respective orientations.
Further, the maximum OHR of 1.6 for all orientations, increased the lighting energy
use by 4.3 kWh/m2, yr (50%); 4.6 kWh/m2, yr (49%); 5.3 kWh/m2, yr (57%) and 5.1
kWh/m2, yr (56%), while reduced the IEUCL by 20 kWh/m2, yr (31%); 15.1 kWh/m2,
yr (24%); 9.6 kWh/m2, yr (18%) and 11.7 kWh/m2, yr (22%) compared to the base
case generic office room, on east, west, north and south orientations respectively.
Relatively high percentage values of IEULt were indicated on the north and
south, which basically received a low natural-light level than the east and west
oriented perimeter zone office rooms. The IEUCL indicated a low percentage of
reduction on north, which received less direct radiation and more diffuse radiation.
The east, west and south perimeter zones received more direct sunlight, thus
eliminated solar heat gains from direct solar radiation than on the north perimeter
zone.
256
4
2
2
Incremental Energy Use (kWh/m ,yr)
6
0
-2
-4
-6
-8
-10
-12
-14
-16
-18
-20
-22
0
0.2
0.4
0.6
IEU CL
0.8
1
Overhang ratio
1.2
IEU Lt
1.4
1.6
IEU Tot
a) East orientation
Incremental Energy Use (kWh/m2,yr)
6
4
2
0
-2
-4
-6
-8
-10
-12
-14
-16
-18
-20
0
0.2
IEU CL
0.4
0.6
0.8
1
Overhang ratio
IEU Lt
1.2
1.4
1.6
IEU Tot
b) West orientation
Figure 6.10 (a & b): Incremental energy use (kWh/m2, yr) for cooling, lighting
and total energy for tested overhang ratios- East and West orientations
257
Incremental Energy Use (kWh/m2,yr)
6
4
2
0
-2
-4
-6
-8
-10
-12
0
0.2
0.4
0.6
0.8
1
1.2
1.4
1.6
Overhang ratio
IEU CL
IEU LT
IEU Tot
c) North orientation
Incremental Energy Use (kWh/m2,yr)
6
4
2
0
-2
-4
-6
-8
-10
-12
-14
0
0.2
0.4
0.6
0.8
1
1.2
1.4
1.6
Overhang ratio
IEU CL
IEU Lt
IEU Tot
d) South orientation
Figure 6.10 (c & d): Incremental energy uses (kWh/m2, yr) for cooling, lighting
and total energy for tested overhang ratios- North and South orientations
Figure 6.10 (a, b, c, & d) illustrate that, IEUCL reach to an optimum value at
overhang ratio between 1.2 and 1.4 on the east and west; between 0.8 and 1.2 on the
north and south orientations, respectively. This can be argued as increase of
overhang ratio reduced the solar heat gains thus reduced the IEUCL, however further
258
increase on overhang ratio have lesser impact on the solar heat gains. At the same
time it can be noticed that increase in overhang ratio reduced the natural-light level
inside the room thus increased the IEULT considerably, which also generated heat
that adds to the space cooling loads. Thus, increase in overhang ratio beyond the
optimum levels indicated an increase on the IEUCL due to the replacement of external
heat gains by the heat gain from artificial lighting.
A similar profile pattern as the IEUCL, was exhibited for the total incremental
electricity use (IEU Tot) (figure 6.10 a, b, c, d). The results indicated a significant
reduction in incremental electricity use with the increase of overhang ratio from 0 to
1.0 on the east and west and 0 to 0.8 on the north and south orientations respectively.
Further increase on overhang ratio indicated an optimum value for IEUTot between
overhang ratios of 1.0 and 1.4 on the east and west orientations, while between
overhang ratios of 0.8 and 1.2 on the north and south orientations. In other words,
within this range the IEUTot lessens the reduction rate and started to increase. But
beyond the above stated range, further increment of the overhang ratio increased the
total incremental electricity use.
Trend analyses were performed to determine the correlation between the
incremental electricity uses and the overhang ratio. Regression equations were
derived from the respective trend analysis’s of incremental electricity use. The
regression analysis has suggested that IEU for lighting can be expressed as a linear
function of the overhang ratio and table 6.9 shows the coefficients obtained for
respective orientations.
IEULt = λ1(OHR)
IEULt: Incremental electricity use for area lighting (kWh/m2, yr)
OHR: Overhang ratio (dimensionless)
λ1,: Regression coefficient
(7.1)
259
Table 6.9: Regression coefficients as a function of overhang ratio for incremental
electricity use for area lighting (IEULt) - East, West, North and South orientations
Orientation
R2
East
West
North
South
0.9878
0.9919
0.9953
0.9946
IEU Lt = λ1(OHR)
λ1
2.5807
2.7551
3.3031
3.1891
The R2 values obtained for all orientations indicated a value above 0.99,
meaning that 99% of the variations in IEU (Lt) can be explained by the variations of
shading overhang ratio. This can be expected since internal natural-light level
through side lighting concept is directly proportional to both the window height and
overhang depth, which is a major component of the lighting load. Although all four
orientations displayed linear correlations, the magnitude of IEULt and the rate of
increase vary, thus the effects of orientation can be observed. As expected, relatively
higher values of regression coefficients were obtained for the north and south
orientations, which basically received low natural-light illuminance due to
introduction of external horizontal shading devices.
Table 6.10 shows the regression coefficients obtained for incremental
electricity use for cooling (IEUCL) on respective orientations. The regression
analysis thus suggests that IEUCL can be expressed as square root function of
overhang ratio (OHR) as follows:
IEUCL = µ1(OHR)2 + µ2(OHR)
(7.2)
IEUCL: Incremental electricity use for space cooling (kWh/m2, yr)
OHR: Overhang ratio (dimensionless)
µ1, µ2,: Regression coefficients
The R2 values indicated above 0.96 on all orientations, emphasizing that 96%
of the variations in IEUCL can be explained by the variations of overhang ratio (table
6.10). This is acceptable, since solar heat gain through the window is directly
260
proportional to both the window height and overhang depth, which is a major
component of the cooling load. Further, as expected the regression coefficients on
the west and east orientations have similar coefficient values, while the south
indicated higher values than the north orientation. The reason can be explained as;
the influence of the solar heat gain is high on the east and west orientations than on
the north and south orientations. In other words, for a particular overhang ratio, the
amount of energy consumed for space cooling is high on the east and west
orientations than on the north and south orientations.
Table 6.10: Regression coefficients as a function of overhang ratio for incremental
electricity use for space cooling (IEUCL) - East, West, North and South orientations
Orientation
East
West
North
South
IEU CL = µ1(OHR)2 + µ2(OHR)
R2
µ2
µ1
0.9952
9.5791
-27.576
0.9949
9.9748
-25.664
0.9585
6.8876
-16.663
0.9716
8.1597
-20.003
Through regression analysis, it has been found that the incremental electricity
use for total energy consumption (cooling + lighting) can be correlated with
horizontal overhang ratio (OHR) as follows:
IEU TOT =η1(OHR)2 + η2(OHR)
(7.3)
IEU TOT: Incremental electricity use for total energy consumption (cooling +
lighting) (kWh/m2, yr)
OHR: Overhang ratio (dimensionless)
η1, η2 : Regression coefficients
Table 6.11 shows the coefficient of determination or the R2 values and
regression coefficient values for respective orientations obtained from regression
analysis. The R2 values for east and west indicated 0.99, while south and north
orientations obtained 0.93 and 0.88 respectively. The R2 value for north (0.88) is
much smaller than the correlation for the IEU Lt and IEU CL. Although cooling
261
penalty due to the solar heat gain exceeds the natural-light benefit, the north facing
windows have relatively smaller heat gains from diffuse solar radiation. Similar to
the IEUCL regression coefficients, the IEU (TOT) has higher values on the west and
east orientations as expected.
Table 6.11:
Regression coefficients as a function of overhang ratio for total
incremental electricity use (IEUTOT) - East, West, North and South orientations.
2
Orientation
R
East
West
North
South
0.992
0.9896
0.8715
0.922
IEU Tot =η1(OHR)2 + η2(OHR)
η1
η2
9.9981
-25.539
10.279
-23.302
6.7698
-13.205
8.2553
-16.937
According to the interpolated energy saving curve, the total incremental
electricity use for optimum energy consumptions were indicated between overhang
ratios of 1.2 to 1.4 on the east, 1.0 to 1.4 on the west, and 0.8 to 1.2 on the north and
south orientations (figure 6.10: a, b, c, & d). The incremental electricity
consumptions were calculated using regression analysis and compared with the eQUEST-3 simulated results, for the tested overhang ratios. Tables 6.12 to 6.14 give
the results of the comparison and the difference is given as a percentage of the eQUEST-3 simulated results. The maximum differences of IEUCL indicated 15.3%
and 12.1% on the north and south orientations for the overhang ratio 0.4. This can be
argued as, overhang ratio 0.4 on north and south orientations eliminated direct solar
radiation by 80% and 70% respectively (see figure. 5.19 Chapter 5). This initial
reduction of direct solar radiation causes significant reduction in cooling energy
consumption compared to other tested overhang ratios. However, the results for
other overhang ratios showed less than 10% difference on all four orientations, which
is an acceptable accuracy. Further, the interpolated values indicated almost no error
for the IEULt except for 17.4% (east), 15.7% (west) and 11.6% (south) differences on
0.6 overhang ratio. All other overhang ratios resulted in less than 10% difference.
262
Table 6.12:
Comparison of simulated (e-QUEST-3) to interpolated (regression
equation) IEUCL (kWh/m2, yr) for tested overhang ratio.
East
West
North
South
OH ratio
Reg.eq
DOE-2
Delta
%
Reg.eq
DOE-2
Delta
%
Reg.eq
DOE-2
Delta
%
Reg.eq
DOE-2
Delta
%
0
-0,3
0,0
0,3
0,0
0,0
0,0
0,0
0,0
-0,5
0,0
0,5
0,0
-0,5
0,0
0,5
0,0
0,2
-5,3
nil
nil
nil
-4,8
nil
nil
nil
-3,4
nil
nil
nil
-4,0
nil
nil
nil
0,4
-9,6
-10,1
-0,5
5,3
-8,7
-8,9
-0,2
2,1
-5,7
-6,8
-1,0
15,3
-6,9
-7,8
-0,9
12,1
0,6
-13,1
-13,5
-0,4
2,6
-11,8
-11,9
-0,1
0,6
-7,6
-7,9
-0,4
5,0
-9,1
-9,6
-0,5
5,5
0,8
-15,9
-15,9
0,0
0,3
-14,1
-13,8
0,3
-2,1
-8,9
-8,5
0,3
-4,1
-10,7
-10,4
0,3
-3,3
1
-17,9
-17,3
0,7
-3,9
-15,7
-15,4
0,3
-1,8
-9,7
-9,0
0,7
-7,9
-11,8
-11,0
0,7
-6,7
1,2
-19,2
nil
nil
nil
-16,4
nil
nil
nil
-10,0
nil
nil
nil
-12,2
nil
nil
nil
1,4
-19,8
-19,5
0,3
-1,6
-16,4
-17,2
-0,8
4,7
-9,8
-9,5
0,3
-3,3
-12,0
-11,6
0,4
-3,3
1,6
-19,6
-20,0
-0,4
2,1
-15,5
-15,1
0,5
-3,0
-9,1
-9,6
-0,5
5,1
-11,2
-11,7
-0,5
4,6
1,8
-18,7
nil
nil
nil
-13,9
nil
nil
nil
-7,9
nil
nil
nil
-9,8
nil
nil
nil
2
-17,1
nil
nil
nil
-11,5
nil
nil
nil
-6,2
nil
nil
nil
-7,7
nil
nil
nil
Table 6.13: Comparison of simulated (e-QUEST-3) to interpolated (regression
equation) IEULt (kWh/m2, yr) for tested overhang ratio
East
West
North
South
OH ratio
Reg.eq
DOE-2
Delta
%
Reg.eq
DOE-2
Delta
%
Reg.eq
DOE-2
Delta
%
Reg.eq
DOE-2
Delta
%
0
-0,2
0,0
0,2
0,0
-0,1
0,0
0,1
0,0
0,0
0,0
0,0
0,0
-0,1
0,0
0,1
0,0
0,2
0,4
nil
nil
nil
0,4
nil
nil
nil
0,7
nil
nil
nil
0,6
nil
nil
nil
0,4
0,9
0,9
0,0
-3,6
1,0
1,0
0,0
-4,9
1,3
1,3
0,0
-2,8
1,2
1,1
-0,1
-7,5
0,6
1,5
1,2
-0,2
-17,5
1,6
1,4
-0,2
-15,7
2,0
1,9
-0,1
-7,6
1,9
1,7
-0,2
-11,7
0,8
2,0
2,0
0,0
0,5
2,2
2,2
0,1
3,4
2,6
2,9
0,2
8,1
2,5
2,7
0,2
7,3
1
2,6
2,5
-0,1
-2,9
2,7
2,7
0,0
-1,3
3,3
3,4
0,1
2,6
3,2
3,2
0,1
1,6
1,2
3,1
nil
nil
nil
3,3
nil
nil
nil
4,0
nil
nil
nil
3,8
nil
nil
nil
1,4
3,7
3,6
0,0
-0,3
3,9
3,9
0,0
-0,3
4,6
4,5
-0,1
-2,2
4,5
4,4
-0,1
-1,2
1,6
4,2
4,3
0,1
3,2
4,5
4,6
0,1
1,9
5,3
5,3
0,0
-0,5
5,1
5,1
0,0
0,2
1,8
4,7
nil
nil
nil
5,0
nil
nil
nil
5,9
nil
nil
nil
5,8
nil
nil
nil
2
5,3
nil
nil
nil
5,6
nil
nil
nil
6,6
nil
nil
nil
6,4
nil
nil
nil
The east and west orientations showed almost no error for the total
incremental electricity use (IEUTot) compared to simulated results (table 6.14). In
both cases, an average of 3.2% and 3.6% differences were shown for the total
incremental electricity use. However, the north orientation indicated the highest
difference of 20% for the overhang ratio 0.4 and more than 10% difference was
263
resulted for the overhang ratio of 1.0 and 1.6. The difference value exceeded 10%
for overhang ratio of 0.4 and 1.0 on the south orientation. Hence, values calculated
using simplified regression method can be accepted to provide design guidance to
determine appropriate overhang ratio for the optimum energy consumption.
Table 6.14: Comparison of simulated (e-QUEST-3) to interpolated (regression
equation) IEUTOT (kWh/m2, yr) for tested overhang ratio
East
West
North
South
OH ratio
0
0,2
0,4
0,6
0,8
1
1,2
1,4
1,6
1,8
2
Reg.eq
DOE-2
Delta
%
Reg.eq
DOE-2
Delta
%
Reg.eq
DOE-2
Delta
%
Reg.eq
DOE-2
Delta
%
-0,4
0,0
0,4
0,0
-0,1
0,0
0,1
0,0
-0,6
0,0
0,6
0,0
-0,6
0,0
0,6
0,0
-4,9
nil
nil
nil
-4,3
nil
nil
nil
-2,7
nil
nil
nil
-3,4
nil
nil
nil
-8,7
-9,3
-0,5
5,7
-7,7
-7,9
-0,2
2,7
-4,4
-5,5
-1,1
19,9
-5,6
-6,7
-1,0
15,4
-11,7
-12,2
-0,5
4,0
-10,3
-10,5
-0,2
2,2
-5,5
-6,1
-0,6
9,4
-7,2
-7,9
-0,7
9,1
-14,0
-13,9
0,1
-0,6
-12,1
-11,6
0,4
-3,8
-6,2
-5,6
0,5
-9,5
-8,2
-7,7
0,5
-7,2
-15,5
-14,8
0,7
-4,7
-13,0
-12,7
0,3
-2,4
-6,3
-5,6
0,8
-13,7
-8,6
-7,8
0,8
-10,3
-16,2
nil
nil
nil
-13,2
nil
nil
nil
-6,0
nil
nil
nil
-8,3
nil
nil
nil
-16,1
-15,9
0,3
-1,8
-12,5
-13,3
-0,8
6,2
-5,2
-5,0
0,2
-4,6
-7,5
-7,2
0,3
-4,6
-15,3
-15,7
-0,4
2,6
-11,0
-10,5
0,4
-4,3
-3,9
-4,3
-0,5
10,6
-6,0
-6,6
-0,5
8,2
-13,7
nil
nil
nil
-8,7
nil
nil
nil
-2,0
nil
nil
nil
-4,0
nil
nil
nil
-11,3
nil
nil
nil
-5,5
nil
nil
nil
0,3
nil
nil
nil
-1,3
nil
nil
nil
Based on above assumptions, energy savings for cooling, lighting and total
electricity use were calculated as a percentage, compared to the base case generic
office room energy consumptions (figure 6.11). As shown in figure 6.11, with the
increase of overhang ratio, energy saving for cooling progressively increased and
optimum energy saving of 31%, 26%, 19% and 22% were indicated at overhang ratio
between 1.4, 1.3, and 1.2 on the east, west and north/ south orientations respectively.
This is almost acceptable as discussed in chapter five (5), where more than 80% to
85% of the direct solar radiation and more than 45% of the diffuse solar radiation on
the west and east orientations were terminated with the overhang ratio of 1.4.
Similarly, more than 80% of direct solar radiation and more than 40% of diffuse
solar radiation were terminated with the overhang ratio of 1.2 on the north and south
orientations. However, the cooling energy saving starts degrading with further
increment of overhang ratio.
264
70
60
50
Energy saving %
40
30
20
10
0
-10
-20
-30
-40
0
0.2
0.4
0.6
0.8
1
1.2
1.4
1.6
1.8
2
Overhang ratio
East CL
East Lt
West CL
West Lt
North CL
North Lt
South CL
South Lt
Figure 6.11: Energy saving percentage for space cooling and area lighting
incremental energy use as a function of overhang ratio, East, West, North and South
orientations
Simultaneously, when cooling energy saving reach the optimum range, the
lighting energy use increased significantly at the respective overhang ratios by 42%,
39%, 43% and 41%, compared to the lighting energy use for the base case generic
office room. As discussed in chapter five (5), at overhang ratio 1.4 (405 lux), 1.3
(390 lux), 1.2 (350 lux) and 1.2 (360 lux), the mean work plane illuminance
indicated bellow 500 lux on respective orientations. Thus, it suggests the need for
electric lighting. Hence, an optimum cooling and lighting energy balance need to be
determined by analyzing the total energy consumption.
The characteristic shape of the total energy saving due to the energy balance
between the overhang ratio and, lighting and cooling energy use is an inverse
polynomial curve (figure 6.12). As the overhang ratio increases, total energy saving
curve progressively degrades up to the overhang ratio of 1.0 (east and west), 0.6
(north) and 0.8 (south) and show very small additional energy saving on further
increase of overhang ratios. Further, when the overhang ratio is at 1.4 (east and
west), 1.2 (north) and 1.3 (south) the energy saving curve starts increasing. Hence,
the optimum energy saving were indicated between overhang ratio of 1.0 to 1.4 on
the east and west, 0.6 to 1.2 on the north and 0.8 to 1.3 on the south orientations
265
respectively. As shown in figure 6.12, about 14%, 11%, 6% and 8% of the total
energy saving were obtained compared to the base case generic office room total
energy consumption on east, west, north and south orientations respectively.
Increasing the overhang ratio to the maximum limit of 2.0 (east and west) and 1.6
(north and south) reduced the total energy saving by about 10% on the east, 4.4% on
the west, 3.6% on the north and 5.6% on the south compared to the base case total
energy consumption, respectively. Therefore, the energy saving values of 14%,
11%, 6% and 8% were determined as optimum savings.
0
0.2
0.4
0.6
0.8
1
1.2
1.4
1.6
1.8
2
0
-2
Energy saving %
-4
-6
-8
-10
-12
-14
-16
Overhang ratio
East Tot
West Tot
North Tot
South Tot
Figure 6.12: Energy saving percentage for total incremental energy use as a
function of overhang ratio, East, West, North and South orientations
The above analysis show that increasing the overhang ratio (by increasing the
overhang depth) had larger impact on the cooling energy saving than the lighting
energy saving. Hence, the external horizontal overhang successfully terminates
maximum amount of solar heat gains through the aperture, while reducing the
natural-light level in the deep end of the room. This reduced the cooling energy
significantly, but artificial lighting was required to maintain the interior lighting
levels. However, the heat gain from lighting is negligible as the room temperature
needs to be exceeded before the lighting heat gain to be affected. Further, the results
266
emphasized that the optimum energy saving can be achieved by manipulating the
external horizontal overhang depth in hot and humid tropical climates like Malaysia.
6.3.2.2 Influence of External Horizontal Overhang on Annual Electricity
Consumption
The energy evaluation was conducted to identify the precision of the
optimum shading geometry and compare it with the solar radiation and natural-light
results obtained in chapter 5. The following section discuses the findings of the
simulation study.
a)
External Horizontal Overhang Ratio: Total Electricity Consumption
The results revealed that the depth of the external overhang influenced the
total energy consumption in perimeter office room. The total energy consumption
exhibited an inverse curved profile with a diminishing return as the depth of the
overhang increased or with the increment of overhang ratio. As observed, respective
optimum energy consumption ranged between overhang ratio of 1.0 and 1.4 on the
east and west orientations, while on north and south between overhang ratio of 0.8
and 1.2, respectively. Regression analyses were performed to determine the
correspondence optimum overhang ratio for optimum energy consumption and to
determine the potential energy savings. In conclusion, the results thus revealed, that
overhang ratio of 1.0 on the north and south, 1.2 on the west and 1.3 on the east
suggested optimum energy savings for respective orientations. The following table
6.15 illustrates the relationship between optimum overhang ratio and the
correspondence optimum energy saving percentages for each orientation compared to
the base-case model. The correspondence mean work plane illuminance at reference
point 2 indicated that the west and south orientations receive above the 500 lux
value. But, on east and north orientations received a lower natural-light illuminance
value for the optimum overhang ratio. Therefore, the required illuminance level on
the east and north oriented perimeter office room was achieved by means of artificial
lighting. The balance between lighting and cooling energy consumptions were
267
attained by the overhang shading depth for an optimum energy reduction. In other
words, an optimum energy reduction can be achieved by having a suitable overhang
shading depth.
Table 6.15:
Summary of total energy saving and respective work plane
illuminance for optimum overhang ratio, East, West, North and South orientations
b)
Orientation
Optimum
overhang
ratio
Percentage of total
energy saving
Mean work plane
illuminance(lux) at
reference point 2
East
West
North
South
1.3
1.2
1.0
1.0
14%(16 kWh/m2,yr)
11% (13.2kWh/m2yr)
6% (6.3 kWh/m2, yr)
8% (8.6 kWh/m2, yr)
423
530
346
516
External Horizontal Overhang Ratio: Electricity Consumption for Space
Cooling
The influence of the overhang ratio on the space cooling load was assessed in
order to determine the optimum overhang depth for optimum energy consumption for
space cooling. The results indicated that the optimum energy savings for space
cooling were obtained for overhang ratio of 1.4, 1.3, and 1.2 on east, west and north/
south orientations respectively. Simultaneously, when cooling energy saving reaches
the optimum range, respective mean work plane illuminance indicated below the
target illuminance (500 lux) on all four orientations. The following table 6.16
illustrates the optimum overhang ratio, their respective energy savings and work
plane illuminance obtained. As indicated, the east orientation has higher cooling
energy saving compared to all other three orientations. This can be explained that
the east orientation has a deep overhang compared to all other three orientations
(which is about 1.4 times the window height). Further, the amounts of work plane
illuminance received were higher on the east and west oriented office room than on
the other orientations for the respective overhang ratios (table 6.16). The results also
showed that work plane illuminance level influenced the cooling energy saving
considerably. For instance, when the work plane illuminance level was decreased,
the energy saving for cooling resulted in high energy saving. But, beyond the
optimum overhang ratio for cooling energy saving (table 6.16), further reduction of
268
work plane illuminance result in reducing the cooling energy saving. This is mainly
due to natural-light is being replaced by artificial lighting. Heat generated from
artificial lighting affect on the cooling energy consumption.
Table 6.16: Summary of energy saving for space cooling and respective work
plane illuminances for optimum overhang ratio, East, West, North and South
orientations
Orientation
Optimum
overhang
ratio
East
West
North
South
1.4
1.3
1.2
1.2
Percentage of energy
saving for space cooling
31% (19.8 kWh/m2)
26% (16.5 kWh/m2)
19% (10 kWh/m2)
22% (12.2 kWh/m2)
Mean work plane
illuminance(lux) at
reference point two
412
505
334
489
Influence of orientation on the optimum overhang depth for optimum energy
saving for space cooling were also assessed. The results showed that the north
orientation obtained the lowest energy saving compared to the south, west and east
orientations. Compared to the north, 22%, 65% and 98% cooling energy savings
were obtained for south, west and east orientations respectively. Similarly,
compared to the west, the east orientation obtained 20% energy saving for space
cooling. This implies that the application of an external horizontal overhang saved
more energy on the east than on the west orientation. In other words, the west
consumed more energy for cooling the space than the east.
c)
External Horizontal Overhang Ratio: Electricity Consumption for Area
Lighting
Lighting energy consumption showed a linear relationship with the increase
of overhang ratio. Increase of overhang ratio reduced the work plane illuminance
thus resulted in increase of energy consumption for artificial lighting. Effects of
optimum overhang ratios for space cooling and total energy consumption on the
lighting energy consumption were also assessed (table 6.17 and 6.18). The results
are illustrated below:
269
Table 6.17: Summary of lighting energy consumption for optimum overhang ratio
for space cooling, East, West, North and South orientations
Orientation
Optimum overhang ratio
for space cooling
East
West
North
South
1.4
1.3
1.2
1.2
Lighting energy
consumption percentage
42% (3.65 kWh/m2)
39% (3.6 kWh/m2)
43% (3.96 kWh/m2)
41% (3.8 kWh/m2)
Table 6.18: Summary of lighting energy consumption for optimum overhang ratio
for total energy consumption, East, West, North and South orientations
Orientation
Optimum overhang ratio for
total energy consumption
East
West
North
South
1.3
1.2
1.0
1.0
Lighting energy
consumption percentage
39% (3.38 kWh/m2)
37% (3.31 kWh/m2)
36% (3.39 kWh/m2)
35% (3.18kWh/m2)
Above figures showed that low lighting energy consumption were indicated
for the optimum overhang ratio for total energy consumption compared to optimum
overhang ratio for cooling energy consumption. The reason can be stated that the
optimum overhang ratios for space cooling are larger than that for the total energy
consumption. Therefore the amount of natural-light received into the space is more
for optimum overhang ratios for total energy consumption than for the space cooling.
Thus, the energy consumption for artificial lighting is less for the latter option of
overhang ratios. This indicates that it is important to compare lighting, cooling and
total energy consumption to determine the optimum overhang ratio for optimum
energy consumption.
6.4 Summary
This chapter analyzed the results obtained for the correspondence office room
cooling loads and energy consumptions for the tested overhang depths (given as
overhang ratio). The cooling load analysis on the base case model enabled to
understand the influence of the building components on the overall heat gains. The
270
results showed that heat gains from window solar radiation and window conduction
were main contributors on the cooling loads. The influences of natural-light
utilization on cooling loads were also analyzed. The results revealed that use of
natural-light and application of shading strategies were two important aspects in
building’s cooling load reduction. The optimum overhang ratios were determined
based on the values obtained for optimum total cooling load on respective
orientations. Influences of orientations on the cooling loads were also discussed.
The results and analyses of the annual electricity consumption were discussed
in three stages. First, the base case model energy consumptions were analyzed with
and without natural-light utilization. The results emphasized the significance of
using natural-light to reduce the building energy consumption. Secondly, influences
of tested overhang on energy consumption were investigated. The analyses were
carried out by calculating the incremental electricity use as function of overhang
ratio. The results emphasized the increment (or decline) of the energy consumption
for the tested overhang solutions, compared to the base-case model. In third section,
regression techniques were used to determine the optimum overhang ratio for
optimum energy consumptions. Mainly, three energy components were analyzed to
understand the correlation between each component when the external shading
strategies were applied; electricity consumption for space cooling, area lighting and
total energy consumption.
Energy consumption of the generic office room was largely influenced by the
natural-light utilization. Use of natural-light, reduced the energy consumption for
lighting. It also increased the energy consumption for space cooling. High energy
was consumed for space cooling in both lighting schemes. Impact of artificial
lighting on energy consumption for space cooling is very low compared to the effect
of natural-light on space cooling energy consumption. Therefore the main criterion
for reducing the energy consumption for cooling is to eliminate the unwanted heat
gain from the building envelope in a perimeter office room while encouraging
natural-light in to the building, in hot and humid climates like in Malaysia. The
overall conclusions of the findings from chapter five (5) and six (6) are presented in
the final chapter.
CHAPTER 7
CONCLUSION
This chapter concludes by summarizing the overall thesis development and
findings from previous Chapters. The application of the research findings are also
discussed in relation to the aims and objectives of the thesis as set in Chapter 1.
Finally, further investigations related to this study are suggested.
7.1 Review of Thesis Objectives and Research Questions
As stated in Chapter 1, the main aim of this thesis was to investigate and
evaluate the impact of the horizontal shading device on the incident solar radiations,
transmitted heat gain and the amount of natural light penetration into the building;
thereby to determine the geometry of horizontal shading device to optimize the
energy savings for cooling and lighting for office buildings in hot and humid
climates. This objective was achieved by using the eQUEST-3, DOE 2.2 dynamic
energy computer simulation program.
This thesis hypothesised that an optimum depth of the horizontal shading
device will provide a balance between solar heat gains and provides adequate natural
light and predicts an optimum energy saving in office buildings under tropical
climate conditions.
272
The following questions were addressed in order to achieve the main
objectives of the thesis:
1. Does the orientation of the fenestration influence the solar heat gain and
daylight penetration into the building and the depth of the shading device?
2. What are the effective overhang ratios to intercept maximum direct and
diffuse incident solar radiations during the over heated period from 9:00 am
to 17:00 pm?
3. What is the effective overhang ratios for maximum reduction of
transmitted heat gains during the over heated period from 9:00 am to 17:00
pm?
4. What is the effective overhang ratio to obtain adequate work plane
illuminance at deep end of the space considered?
5. Does the effective depth obtained at (2) that reduced the work plane
illuminance below the target level?
6. What is the trade off between the transmitted heat gain and the shading
depth to achieve target work plane illuminance?
7. What is the optimum shading geometry to obtain an optimum energy
saving in relation to cardinal orientations?
7.2 Thesis Conclusion
This section attempts to conclude the research by summarizing the major
findings of the research and answering the research questions as stated. They are as
follows:
273
7.2.1 External Horizontal Overhang and Solar Radiation
1)
The maximum total incident solar radiation (direct and diffuse) on the base
case model demonstrated that the west orientation received the highest and the north
received the least amount of total incident solar radiation. In comparison, the east,
north and south received 4%, 57% and 34% less total incident solar radiation than the
west orientation. Therefore, it is important to consider the direct and diffuse solar
radiation in thermal design decisions especially in high availability of diffuse solar
radiation under clear sky conditions. This indicates that building facades without any
external environmental protections should be oriented towards the north-south and
avoid east-west orientations.
2)
The incident direct solar radiation is high on the east orientation and the north
received the minimum direct solar radiation on the bare window. The results were
compared on each orientation. The west, north and south received 16%, 76%, and
44% less direct solar radiation than on the east window. Also the results indicated
that intensity of incident direct radiation is high during morning hours on the east
orientation than in the evening hours on the west orientation. The following
overhang ratios were required for each orientation to reduce the incident direct solar
radiation more than 80 percent:
3)
o
Overhang ratio 1.2, East orientation
o
Overhang ratio 1.6, West orientation
o
Overhang ratio 0.6, North orientation
o
Overhang ratio 0.8, South orientation
Increase in overhang depth had lesser impact on the amount of diffuse solar
radiation received on the window pane. Hence, the results indicated that use of
maximum overhang ratio (east/ west OHR of 1.6 and north/ south OHR of 1.4) on all
orientations could only reduce less than 50% of the incident diffused solar radiation
on the bare window. Therefore determining the overhang depth based on diffuse
solar radiation may result in deeper overhang depths; as well this might reduce
beneficial natural light into the space.
274
4)
Application of overhang ratio of 1.4 on the north and south indicated 35.9%
and 38.3% total heat gain reduction respectively compared to heat gain through the
bare window. Similarly, the east and west indicated 48.9% and 45.4% total heat gain
reduction when overhang ratio is 1.6 compared to the base case option. Further
increment of above stated overhang ratios had little effect on the transmitted heat
gains. Influence of overhang ratios of 1.4 and 1.6 on different solar radiation
components indicated that the external horizontal overhang have significant impact
on the direct solar radiation than on other solar radiation components under tropical
sky conditions (table 7.1).
Table 7.1: Influence of maximum overhang ratio on direct, diffused solar radiation
and total transmitted heat gain, East, West, North and South orientations
5)
Diffuse
incident solar
radiation
(% of
reduction)
Total
transmitted
heat gain
(% of
reduction)
Orientation
Overhang
ratio
Direct incident
solar radiation
(% of
reduction)
East
1.6
90.0%
46.0%
49.0%
West
1.6
80.0%
47.5%
45.4%
North
1.4
85.3%
42.3%
36.0%
South
1.4
85.4%
43.4%
38.3%
Application of the external horizontal overhang shifted the peak heat gain
hour outside the working hour time on the east and west orientations. Increase of
overhang depth reduced the intensity on all orientations. These variations can be
combined with operation time as an energy efficient measure.
6)
Simple graphs were developed to determine the influence of horizontal
shading strategies on different solar radiation components; the direct and diffuse
incident solar radiation, and transmitted heat gains, for perimeter office buildings
under tropical climatic conditions (figure 5.19, 5.20 and 5.21 in chapter 5). These
graphs can be used to determine the appropriate external horizontal shading
configurations at early design stage.
275
7.2.2 External Horizontal Overhang and Work Plane Illuminance
1)
The absolute work plane illuminance at reference points were determined by
three natural light sources; the direct sunlight, diffuse sky light and reflected light.
The relationship between the external overhang depth and the work plane
illuminance levels demonstrated that when the depth of external overhang increases,
the illuminance level decreased. The mean work plane illuminances were calculated
for each orientation to determine the optimum overhang ratios in order to achieve the
target illuminance level of 500 lux. The results were as follows:
o
Overhang ratio 1.0, East orientation
o
Overhang ratio 1.3, West orientation
o
Overhang ratio 0.2, North orientation
o
Overhang ratio 1.0, South orientation
2)
The relationship between the natural light penetration depth and the window
height were determined based on the assumptions of, that the depth of the room
begins at the outer edge of the overhang and the influence of window sill was
disregarded. The expected illuminance level at deep end was set as 500 lux. Thus,
the results suggested that the natural light penetration reached up to following depths
of the room considered on respective orientations:
o
East 4.3 time’s height of aperture
o
West 4.5 times height of aperture
o
North 3.5 times height of aperture
o
South 4.3 times height of aperture.
This indicates when considering only the natural illuminance, the east, west
and south orientations can have deep plan office spaces. All orientations illustrated
deeper natural light penetration under Malaysian sky conditions compared to the
common rule of thumb of 2.5 times height of the window.
276
4)
Hourly influence of the minimum work plane illuminance were observed at
reference point two, which is located at the deep end of the room opposite to the
window pane. Increase of overhang ratio shift the peak illuminance and also reduced
the intensity of the illuminance on the east and west orientations. However, this
pattern was not illustrated on the north and south orientations, but the illuminance
hours above target level decreased with the increase of overhang ratio. This implies
that the overhang depth reduced the brightness of the work plane illuminance by
obstructing the direct sunlight and maintains a constant illuminance level at
respective reference point. These patterns can be combined with work operation or
building operation schedules to obtain the maximum advantage of the natural light
into the buildings.
5)
The study revealed following external overhang ratios with respect to
influence of the direct solar radiation, total heat gain and target work plane
illuminance level (table 7.2). Considering the optimum overhang ratio for maximum
reduction of the direct solar radiation indicated as a better shading strategy on the
east, west and south orientations, under tropical sky conditions. These shading
options reduced more than 80% of the direct solar radiation, and maintained adequate
level of work plane illuminance (between 448 lux and 545 lux) compared to other
two overhang ratio options, for respective orientations. However, on north
orientation, design of external horizontal overhang depends on the amount of natural
light penetration than reducing solar heat gains into the space. Yet, the optimum
overhang depth for maximum reduction of transmitted heat gain only received mean
illuminance level above 300 lux, which still provides adequate natural lighting for
general reading and writing at the back of the perimeter office space.
277
Table 7.2:
Trade-Off between optimum overhang ratios and performance
variables for direct incident solar radiation, transmittance heat gain and mean work
plane illuminance, East, West, North and South orientations
Orientation
Optimum OHR
for maximum
obstruction of
direct incident
solar radiation
Direct
incident
solar
radiation(%
of reduction)
Total
transmitted
heat gain
(% of
reduction)
Mean minimum
work plane
illuminance (lux)
at ref.point 02
East
West
North
South
1.2
1.6
0.6
0.8
82.0%
81.4%
84.0%
84.6%
44.0%
45.4%
27.9%
33.3%
448
448
417
545
Orientation
Optimum OHR
for maximum
reduction of
total heat gain
Direct
incident
solar
radiation(%
of reduction)
Total
transmitted
heat gain
(% of
reduction)
Mean minimum
work plane
illuminance (lux)
at ref.point 02
East
West
North
South
1.6
1.6
1.4
1.4
90.0%
80.0%
85.3%
85.4%
48.9%
45.4%
35.9%
38.3%
370
448
322
464
Orientation
Optimum OHR
for mean target
work plane
illuminance
Direct
incident
solar
radiation(%
of reduction)
Total
transmitted
heat gain
(% of
reduction)
Mean minimum
work plane
illuminance (lux)
at ref.point 02
East
West
North
South
1.0
1.3
0.2
1.0
77.6%
76.7%
52.2%
85.3%
41.4%
42.4%
14.1%
35.4%
500
500
500
500
7.2.3 Base-case Generic Office Room and Building Component Cooling Loads
1)
The investigation of the base-case model showed that window solar radiation
and window conduction heat gains were prime sources of building envelope heat
gains for both with and without natural-light utilization schemes. The contribution of
window conduction and solar heat gains (with natural-light utilization) on respective
orientation was given as a percentage of total envelope cooling loads and presented
as following:
o
On east and west: window conduction 22% and solar radiation heat gain
57%
278
2)
o
On north: window conduction 27% and solar radiation heat gain 48%
o
On south: window conduction 26% and solar radiation heat gain 50%
The internal cooling loads were determined by the heat gains from the
internal lighting, occupancy heat gains and heat gains from equipments. The impact
of natural light on building cooling load was determined by comparing without
natural-light base-case model. The results obtained for without natural light
utilization option showed increase of internal cooling loads by 14% on the east and
west orientations, while 18% and 17% on the north and south orientations compared
to the base-case with natural-light. Hence, it can be concluded, that for a perimeter
office room, impact of the internal lighting on building cooling load was low
compared to the cooling loads due to solar heat gain with natural-light utilization.
However, when natural-light was not utilized, a significant amount of heat was
released by the internal lighting system which needs to be removed by the HVAC
system. The effect of internal lighting heat gain may increase in deep plan office
buildings where natural-light cannot be reached to the deep end of the space. Also,
the amount of heat released by internal lighting system may differ depending on
different light sources, e.g. Fluorescent lamps may generate less heat compared to
incandescent lamps. Hence, total rejection of beneficial climatic forces such as
natural-lighting increases the cooling loads in perimeter office buildings.
7.2.4 External Horizontal Overhang and Building Component Cooling Loads
1)
Application of the external horizontal overhang had an influenced on window
solar heat gain, window conduction and on lighting heat gains. Results revealed that
an increase in overhang ratio significantly reduced the window solar cooling loads,
while the lighting cooling load was increased. However, application of maximum
shading illustrated an increase in window conduction cooling loads on all
orientations. Optimum total cooling loads were obtained for the following overhang
ratios on each orientation:
279
2)
o
Overhang ratio 1.4, east and west orientations
o
Overhang ratio 1.0, north and south orientations
Comparison of cooling loads for window conduction, window solar radiation
and internal lighting on each orientation illustrated that the west oriented office room
had high cooling load, while the north indicated low cooling load reduction
compared to other orientation for optimum overhang ratios (table 7.3). Overall, the
impact of shading device depth had significant impact on the east and west
orientations than on the north and south orientations.
Table 7.3:
Trade-Off between optimum overhang ratio and building cooling load
components, East, West, North and South orientations
Orientation
Optimum
overhang
ratio
East
1.4
West
1.4
North
1.0
South
1.0
3)
Window
conduction
cooling load
& reduction
percentage
1.68 MWh
(6.9%)
1.7 MWh
(5.4%)
1.66 MWh
(1.6%)
1.66 MWh
(3.0%)
Solar
radiation
cooling load
& reduction
percentage
1.75 MWh
(62%)
1.96 MWh
(57%)
1.60 MWh
(47%)
1.68 MWh
(50%)
Internal
lighting
cooling load
& reduction
percentage
0.42 MWh
(42%)
0.45 MWh
(41.9%)
0.43 MWh
(37%)
0.42 MWh
(35%)
Total
cooling load
& reduction
percentage
5.1 MWh
(36%)
5.37 MWh
(33%)
4.91 MWh
(21%)
5.01 MWh
(25%)
Comparison between building cooling loads with and without natural-light
utilization when shading strategies were applied, suggested that both shading and
natural-light utilization were required to reduce annual building cooling loads.
However, in case of either one option is being applied, use of shading strategy
revealed better saving in cooling load reduction than use of natural-light in perimeter
office buildings. Thus, this suggests that the use of shading device is more effective
in reducing the building cooling load than use of natural-light in hot and humid
tropical climates. However, neglecting both solar radiation and natural-light
eventually resulted in high building cooling loads.
280
7.2.5 Base-case Generic Office Room and Energy Consumption
1)
Total energy consumption for the designated generic office room was well
below the Malaysian Standard (135 kWh/m2) for all orientations. This implies that
application of Malaysian Standard (MS1525: 2001) generally resulted in energy
consumption within the energy efficient range with natural-light utilization.
However, when natural-light was not utilized for internal illuminance, the results
indicated that energy consumption for a perimeter office exceeded the standard
range, by 17.2%, 16.2%, 8.5% and 10.0% on the east, west, north and south
orientations respectively.
2)
When natural light is not utilized, the total energy consumption was increased
by 36% on the east and west, 40% on the north and 39% on the south compared to
the base case energy consumptions with natural light utilization. Hence, natural-light
utilization is an important factor in energy efficient building design for Malaysia.
3)
The results indicated that, energy use related to the HVAC system were the
most important components (space cooling and vent fan) in all four orientations
considered. Energy consumption for space cooling was high with natural-light
utilization compared to without natural-light utilization. Hence, natural-light
utilization also increased energy consumption for space cooling. This is mainly due
to the heat generated from the direct sunlight. The east and west oriented office
rooms consumed more energy for space cooling compared to the north and south
orientations in Malaysia.
4)
Electricity consumption for area lighting had the least energy usage in a
perimeter generic office room with natural-light utilization. The results showed,
when natural-light was not used for internal lighting, electricity consumption for area
lighting resulted in an increase of 27% on the east and west, while 29% on the north
and south of the total energy use respectively.
281
5)
The investigation also revealed that the orientation of the office room
influenced the energy consumption for space cooling, but had no effect on the
lighting energy consumption. The east and west orientations indicated high
electricity consumption for space cooling than the north and south orientations. The
north orientation indicated the lowest energy consumption for space cooling. In
perimeter office rooms, adequate natural illumination were received irrespective of
the orientation, which accounts for about 80% of the lighting energy saving in all
orientations considered.
7.2.6 External Horizontal Overhang and Building Energy Consumption
1)
Optimum total energy savings were obtained for the following overhang
ratios on respective orientations:
o
Overhang ratio 1.3, obtained 14% energy saving on east orientation
o
Overhang ratio 1.2, obtained 11% energy saving on west orientation
o
Overhang ratio 1.0, obtained 6% energy saving on north orientation
o
Overhang ratio 1.0, obtained 8% energy saving on south orientation
2)
The maximum cooling energy savings were obtained on the east while north
orientations showed the minimum energy saving for space cooling. Optimum energy
consumptions for space cooling were obtained for the following overhang ratios:
o
Overhang ratio 1.4 obtained 31% cooling energy saving on east orientation.
o
Overhang ratio 1.3 obtained 26% cooling energy saving on west orientation.
o
Overhang ratio 1.2 obtained 19% and 22% cooling energy saving on north
and south orientation respectively.
3)
Increase in overhang depth consequently increases the lighting energy
consumption. This is due to the reduction in natural lighting to perform the required
tasks in the particular room. The lighting energy consumption with the optimum
282
overhang ratio revealed low percentage of the total energy saving compared to the
optimum overhang ratio for space cooling (table 7.4).
4)
Observations on the internal mean illuminance level revealed that optimum
overhang depths for total energy consumption received more natural light than
optimum overhang depths for space cooling (table 7.4). The results showed that the
west and south oriented office room received the required level of illuminance
(above 500 lux), while the east and north oriented spaces received below the target
illuminance level. However, for both optimum overhang options, the mean
illuminance was adequate for general illuminance of office space (above 300 lux) on
all orientations.
Optimum
OHR for
Total
Energy
consumpt
ion
East
1.3
West
1.2
North
1.0
South
1.0
Orientation
Orientation
Table 7.4: Summary of optimum overhang ratio for total energy consumption and
space cooling energy consumption
Optimum
OHR for
Space
cooling
Energy
consumpt
ion
East
1.4
West
1.3
North
1.2
South
1.2
Percentage of
total energy
saving
Energy saving
% for space
cooling
Lighting
energy
consumption
%
14%
(16 kWh/m2,yr)
11%
(13.2kWh/m2yr
6%
(6.3 kWh/m2yr)
8%
(8.6 kWh/m2yr)
30.7%
(19.5kWh/m2,yr)
26%
(16.4kWh/m2,yr)
19%
(9.7 kWh/m2,yr)
22%
(11.8kWh/m2,yr)
39%
(3.38 kWh/m2)
37%
(3.31 kWh/m2)
36%
(3.39 kWh/m2)
35%
(3.18kWh/m2)
Percentage of
total energy
saving
Energy saving
% for space
cooling
Lighting
energy
consumption
%
13.9%
(16.1 kWh/m2)
11%
(12.8 kWh/m2)
5.8%
(6.1 kWh/m2)
7.8%
(8.4 kWh/m2)
31%
(19.8 kWh/m2)
26%
(16.5 kWh/m2)
19.3%
(10 kWh/m2)
22.5%
(12.2 kWh/m2)
42%
(3.65 kWh/m2)
39%
(3.6 kWh/m2)
43%
(3.96 kWh/m2)
41%
(3.8 kWh/m2)
Mean
minimum
WPI (lux)
at ref.pt
02
423
530
346
516
Mean
minimum
WPI(lux)
at ref. pt
02
412
505
334
489
283
Application of the external horizontal shading strategies on the east and west
orientations resulted in better energy saving than on the north and south orientations.
This is mainly due to the high energy saving on space cooling and adequate natural
lighting levels obtained on east and west orientations. Although work plane
illuminance on the south office room was over 500 lux, energy saving for space
cooling indicated low percentage value compared to the east and west orientations
(table 7.4).
5)
Simple graphs were developed to determine the optimum energy savings for
typical perimeter office building based on different horizontal overhang ratios under
tropical climatic conditions (figure 6.11 and 6.12 in Chapter 6).
7.2.7 Optimum Overhang Ratios for Hot Humid Tropical Climate
1)
As discussed in chapter 5 and 6, the optimum overhang ratio for the
following performance variables were experimented; incident solar radiation, total
transmitted heat gains, work plane illuminance, building cooling loads, electrical
consumption for cooling and total energy consumption. The study indicated that the
depth of simple external horizontal overhang can be manipulated to control the
internal thermal and lighting conditions of building. Thus, it allows us to determine
the buildings energy use. The finding suggested several optimum solutions for
respective performance variables as illustrated bellow (table 7.5).
2)
According to table 7.5, values suggested by the simulation results indicated
lesser overhang ratios compared to overhang ratio predicted by the incident angle on
the east and west orientations. Considering the incident angle attributes to all angles
of incidence; therefore larger overhang ratio is required to intercept all angles of
incident direct solar radiation. However, overhang ratios on the north and south
orientations indicated almost within the same rage on both methods (OHR between
minimum of 0.6 and maximum of 1.2). The reason can be stated as due to the
284
influence of diffuse solar radiation is high on the north and south orientations
compared to the direct solar radiation.
Table 7.5: Summary of optimum overhang ratio for various performance variables
on east, west, north and south orientations for tropical climate
Overhang Description
East West North South
Optimum OHR for incident solar radiation
Optimum OHR for target work plane
illuminance
Optimum OHR for building cooling load
Optimum OHR for energy consumption for
space cooling
Optimum OHR for total energy consumption
Overhang ratio predicted based on incident
angles of direct solar radiation
3)
1.2
1.6
0.6
0.8
1.0
1.3
0.2
1.0
1.4
1.4
1.0
1.0
1.4
1.3
1.2
1.2
1.3
1.2
1.0
1.0
1.7
2.5
0.8
0.6
Use of overhang ratio (or Projection Factor - PF) give several options for the
architect to design the shading strategies and also provides a visual picture of the
impact of environmental control alternatives on the built environment; for e.g. an
overhang ratio of 0.8 (south orientation) can be designed as horizontal louvers
maintaining the same overhang ratio (figure 7.1). However, it is important to note
that impact of solar radiation and natural light penetration may change due to the
reflection from the louver surfaces. As a result it may affect on the overall energy
consumptions of the building considered.
0.8x
0.8x
0.8x
x
x
x
x
x
x
Figure 7.1: Several design option of external horizontal overhang shading device
285
7.3 Application of The eQUEST-3 (DOE 2.2) Energy Simulation in Malaysian
Conditions
1)
The conclusions of this study are based on the results obtained with the
computer simulation eQUEST-3, which is supported by the DOE 2.2 calculation
engines. Therefore the results bear the limitations and accuracy of the computer
program used. These limitations have been acknowledged and discussed in the
methodology (Chapter 4). Other limitations encountered during the experiments are
as follows:
o
External shading more than 3 meters deep is not acceptable for daylight
calculations
o
Absolute work plane illuminance includes both the direct sunlight and the
diffuse light, which limited in calculating the daylight factor for each hour.
o
Work plane illuminance values were evaluated assuming the office room is
empty or without internal partitions and furniture. Therefore when internal
elements are incorporated the illuminance level may reduce.
o
For accurate daylight calculation, the weather data need to be formatted in
TMY2 files with measured solar radiation
2)
The eQUEST-3 program was tested for Malaysian conditions to study on the
interaction between the building (and elements), system operations, occupancy
schedules and climatic influences to determine the thermal exchange, natural light
and energy performance of the correspondence office room. The provisions for
following data input suggested the acceptability to use the program in hot and humid
tropical climate conditions:
o
Selection of location with required weather data (recommended format) for
the specific location, atmospheric turbidity, sky clearness number, external
ground temperature
o
Selection of required function of the building
286
o
Selection of daylight utilization option and blocking the heat load
calculations
3)
o
Selection of analysis year
o
Selection of different orientations
o
Adjustments on thermostat set points
o
Selection of required HVAC system
o
Selection of materials and recommended thermo physical properties
o
Selection of operation schedules
Comparison of the weather data from the weather files (DOE. Weather file
for Kula Lumpur) with measured data obtained for Subang Meteorological Station,
showed relatively similar conditions. Therefore, these input data has given great
confidence in the application of the model in Malaysian conditions for thermal,
natural-light and building energy performances.
4)
The eQUEST-3 is a free available tool which can be successfully use to
analyze building performances, with respect to natural-light, solar heat gains, HVAC
system analysis, lighting, cooling and heating energy consumption. This program is
well equipped with updated information and provides self study manuals to operate
the program. Although it may take time to understand the program and laborious in
operation, it still provides accurate and detail analysis of state-of –art building
technology. These free software tools (including Radiance developed by Greg
Ward) provide information which can be used to do detail analysis of building
performances with reliable accuracy. Hence, use of the eQUEST-3 dynamic energy
simulation tool with respect to the performance of the external shading strategy has
been proved useful in this study.
7.4 Suggestions for Further Research
This study has suggested how a simple external horizontal shading system
can be effectively used to optimize the reduction of the solar heat gains, optimize
287
internal natural lighting and to optimize energy savings. In other words little had
been known about the relationship between the energy use and the external
horizontal shading device geometry. Therefore, the solar shading design strategies
require a rethinking in light of energy efficiency. However, several areas of study
need further investigation, to develop the knowledge of the shading strategies in
Malaysia and regions with similar climates. The following are some suggestions:
1)
Investigation on the effectiveness of the geometry. Apart from the depth of
the overhang, the other factors need to be investigated are; the impact of angle and
the width of the overhang with respect to, daylight, solar heat gain and overall energy
consumption.
2)
Investigation on the effectiveness of surface material and colour of shading
devices on energy consumption. Effectiveness of shading device also depends on the
material and surface colours as they affect on thermal and daylight reflection.
Therefore, these aspects need to be studied in terms of surface texture, light and dark
colours etc. It may also contribute to the aesthetics of the shading device.
3)
Further investigations are required to determine the effects of external
shading strategy on deep plan office buildings and on various building forms.
4)
In terms of daylight, the influence of energy efficient shading strategy on
daylight quality and glare need to be explored. In hot and humid tropics, glare from
window create visual discomforts on the inhabitants and quality of daylight is not
incorporated as design criteria in buildings. Therefore, information on relationship
between shading strategies, daylight quality, glare and energy consumption are very
important.
5)
Investigation of other different external shading devices and their influence
on energy consumption. A detail study should be carried out to look into the impact
of horizontal fins, vertical and egg-crate external shading devices on daylight
penetration, solar heat gain and on energy consumption.
288
6)
Further studies need to be carried out to develop a method to define shading
devices by considering the total solar energy transmittance. In hot and humid tropics
influence of diffuse component of solar radiation on thermal effects are significant.
Therefore, considering the total solar energy transmittance may be an important
aspect in determining different shading strategies. Considering the total solar energy
transmittance may also be a better replacement for defining shading devices rather
than based on shading coefficient. Studies on solar transmittance properties can be
used to develop a design method to determine different shading strategies for the
tropics.
7)
Investigation on the influence of solar shading strategies on the OTTV
(overall thermal transfer value) standards. The standard design criterion for nonresidential building envelope is determined by the OTTV, which is developed based
on solar heat gain through the building envelope. The scope may extend to
determine the influence of solar shading strategy on building OTTV and on the
overall energy consumption of the building. By investigating this aspect, it would
alleviate the problem of trade off between daylight, solar heat gain, use of artificial
lighting and overall energy consumptions.
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APPENDICES
A
Summary of Energy Related Research
C
Summary of High-Rise Office Building and Energy
Use Review
C1. Office Buildings Energy Data Base
Kuala Lumpur, Malaysia
C2. South East Asian Office Building Information
C3. Design of Shading Device Considering the
Windows Solar Angle Dependent Properties:
With Special Reference to Kuala Lumpur Hot
and Humid Tropical Climates
D
Review of Computer Simulation Programs
E
Simulation Data and Results
E1. Sample of Input Data
E2. Summary: Direct and Diffused Incident Solar
Radiation and Transmitted Heat Gains
E3. Summary: Work Plane Illuminance at Ref.Pt:01
and Ref.Pt:02
F
F1 Summary: Building Cooling Load Data
F2 Summary: End Use Energy Consumption Data
(with natural light)
306
307
308
309
310
311
312
313
314
315
Appendix C3
Design of Shading Device Considering the Windows Solar Angle Dependent
Properties: With Special Reference to Kuala Lumpur
Hot Humid Tropical Climate
1.0 Introduction
Use of solar path diagram and shading mask to determine the shading device
geometry only consider the direct incident solar radiation. Thus, shading is generally
design to exclude direct solar radiation penetration in to the building. Due to the fact
they only indicate as a fraction to direct solar radiation, “unshaded” or “shaded”.
However, the above methods do not determine the amount of solar energy
transmitted in to the interior through the fenestration. This implies both short wave
and long wave radiation transmission need to be considered in determining shading
devices.
The phenomenon of g-value was deployed by Dubois (2000) and Kuhn et.al
(2000) as a reference to determine effectiveness of the shading devices. Dubois
(2000) developed a method using the g-values of the window glass to determine the
shading depth for temperate climate condition and for latitude 590 north. The analysis
was tested only for south and west orientations. The developed chart was based on
Mazria’s solar path projection.
1.1 Objective
The main objective of this study is to determine shading device geometry
using incidence angle and direct beam solar radiation transmittance for east, west,
north and south orientations under tropical climate conditions. A normal 3mm thick
single pane glass is being used as the reference glazing.
316
2.0 Definition
2.1 g-Value as a measure of solar gain
To assess the solar thermal gains through fenestration, the total solar energy
transmittance was used as a measurement. The total solar energy transmittance (gvalue) specifies the total fraction of incident solar energy that is transmitted through
the fenestration system. The fenestration system implies both the shading device and
the window system.
The g-value can be expressed (Dubois, 2000):
Gsys
=
Total Solar Energy Transmittance
Incidence Solar Radiation on the facade
(1)
Gsys
=
Qsun
IG* Aw
(2)
Defining the shading device is made according to the direct radiation. This
assumption was made since direct radiation is dominant on clear days when shading
is needed and diffuse radiation is desirable as a source of daylight in the building.
However, the diffuse component should also be considered when the shading device
is mainly used for glare control.
3.0 Method
3.1 The incident angle
Intensity of direct solar radiation on any surface for a given atmospheric
condition can be determined from the value of intensity of direct normal radiation. If
Ibv denotes the direct solar intensity on a given window surface and the angle
between normal to the surface and solar beam is (θ), then Ii is given by;
Ibv = Idn x Cos (θ )
(3)
317
Idn is the intensity of the direct normal radiation. Assuming for a given
incident angle of (θ ), the relationship between Ibv and Idn is a constant (Kθ). Thus,
it can be expressed as;
Cos (θ ) = Ibv / Idn = Kθ
(4)
3.2 The window g-value
The solar heat transmission through a glazing is higher when the solar
radiation incident perpendicular on the glazing surface. The energy received by the
surface decreases when the solar beam moves away from the window normal. The
window g-value indicates which portion of the incident solar radiation is transmitted
and absorbed by the window and become heat in building.
The solar heat gain is expressed by the transmission and absorption
coefficients as polynomials in the cosine of the solar incidence angle (figure 1).
Transmittance and absorptance properties for glazing are developed by Roos and
Karlsson (1998).
1
0.9
Solar Transmittance
0.8
0.7
0.6
0.5
0.4
0.3
0.2
0.1
0
0°
10°
20°
30°
40°
50°
60°
70°
80°
90°
Angle of Incidence
Solar transmittance
Visible transmittance
Solar absorptance
Figure 1. The solar transmittance (g-value), visible transmittance and solar
absorptance for single clear glass window as a function of the angle of incidence
Transmission (τ) and absorptance (α) coefficients were determined for direct
and diffuse solar radiation as follows:
318
Hourly solar heat gain on a vertical window surface, Qsolv (W/m2) is given by:
Qsolv = Ibv (τb +Niαb) + İdv (τd +Ni αd)
(5)
Since only direct solar radiation is considered,
Direct Radiation:
Qsol, b = Ibv (τb +Niαb)
(6)
Where,
gb = (τb +Niαb)
(7)
τ = C1 + C2Cos (θ) + C3Cos2 (θ) + C4Cos3 (θ) + C5Cos4 (θ) + C6Cos5 (θ)
(8)
And
α = A1 + A2Cos (θ) + A3Cos2 (θ) + A4Cos3 (θ) + A5Cos4 (θ) + A6Cos5 (θ)
(9)
For diffuse radiation, Stephenson (1965) calculated τdif and αdif to be 0.799
and 0.0544 respectively. Values of the constants C1, C2, C3, C4, C5 & C6 and A1,
A2, A3, A4, A5 & A6 depends on the glass type and the number of panes. Referred
values were obtained from the DOE 2.2 Engineering manual.
The inward flowing fraction Ni of the absorbed radiation can be expressed as:
Ni = hi / (hi + ho)
(10)
Where hi and ho are the heat transfer coefficients of the inside and out side
glazing surfaces respectively, given in W/m2 K. Inward flowing fraction for single
glazing is 0.268, reference to ASHRAE fundamentals, (1993). This value is used for
present calculations.
Hence, the secondary heat transmission from the absorbed solar radiation can
be given as:
319
τa = Ni α = 0.268 * α
(11)
Based on the above theoretical assumptions hourly values were derived from
the simulation. Then correspondent g-values were determined for each set of solar
altitude (β) and azimuth (φ) angles using the fundamental solar geometrical
relationship. However g-values for direct solar radiation is taken into consideration
as the diffuse component of radiations are independent of the sun position.
Cos (θ ) = Cos (β)* Cos (φ -ψ)
(12)
Where (ψ), is the orientation of the façade from the same reference direction
as the solar azimuth. If the sun is behind the façade (φ -ψ) >90 or –ve value is
indicated.
The gθ − values obtain from the above method is the g-value for the reference
window. By normalizing the gθ values with g0 base value, (which is the maximum
transmittance for any given angle, means when the angle of incidence is zero) and
the new g value can be plotted according to the solar projection and super impose on
a solar path diagram.
G = gθ / g 0
(13)
The nomenclature for G is represented by ‘g-value’, which implies the
fraction of incidence direct solar radiation (Ibv) transmitted into the interior through
the corresponding glass window. The plotted normalized g value is represented by a
concentric circle. The inner most circle encompasses the solar position for the g>0.9
value, the second innermost circle for g>0.8 and the third g>0.7 so on. Hence, g>0.7
value implies that 70% of solar radiation from g0 value is transmitted into the interior
through the window pane.
320
3.3 GCos-value
Values obtain for Κθ (Eq. 4) and g (θ) (Eq.12) from step one and two can be
combined into one single value and define it as GCos-value. This also can be called
as cosine weighted solar angle dependent g-value, Duboi (2000). Hence, for a given
incident angle (x), it can be stated as:
G(x) Cos(x) = g (x)*K (x)
(14)
The GCos-value thus specifies the fraction of direct normal solar radiation
(Idn) that is transmitted in to the building through the window opening. The
calculated GCos values using Subang Jaya Meteorological data for east, west, north
and south orientations were shown in the following tables (1a, 1b, 1c & 1d). For East
and West orientations values were obtain on all twelve months. North orientation
data were tabulated for April, May, June, July and August as the direct solar
radiation falls on this façade only during these months. South orientation data were
collected during the months of January, February, March, September, October,
November and December. One day is selected for each month to understand the
correlation between each parameter described in above steps. These dates were
assumed to be the maximum solar radiation received for respective months.
However, for further analysis, months with highest GCos values, maximum incident
and transmitted values were selected.
The obtained G(x)Cos(x) values were normalized with G(0)Cos(0) base value,
(which is the maximum value for any given angle, when the angle of incidence is
zero) and the new GCos- value can be plotted according to the solar projection and
super impose on a solar path diagram as for g-value in step two. Similar to g-value,
each GCos value encompasses solar position at given altitude and azimuth angle.
E.g. Maximum values of GCos>0.9 delimits the inner most circle, GCos>0.8 next
inner most circle and GCos>0.7 third inner circle so forth.
321
3.4 Direct solar gain
The intensity of the solar radiation varies throughout the day and the year
depending on the location and the atmospheric conditions. The intensity direct solar
radiation (Ibv) can be calculated on any surface for given atmospheric conditions
using equation, (Eq. 3). Hence, total solar gain due to direct solar radiation can be
obtained by;
Qsol = Idn . GCos. A
(15)
Where A is the window area.
The values of Qsol is calculated using solar radiation data obtained from
Subang Meteorological Station, in Kuala Lumpur and compared with window GCosvalues for the main cardinal orientations, (Table 1a, 1b, 1c, 1d).
Table 1a: East Orientation
Day/
Month
2801
2302
2103
Hour
Sol.Alt
Incid.Ang
VSA
OHR
gvalue
GCosvalue
SMS
sol.rad
(W/m2)
Qsol
(W/m2)
8
14
24.1
14.8
3.77
1.00
0.91
269
246
9
28
35.5
30.0
1.74
0.99
0.81
453
367
10
41.5
48.6
45.1
1.00
0.97
0.64
553
354
11
54.2
62.5
60.4
0.57
0.88
0.41
580
236
12
64.4
76.6
75.6
0.26
0.61
0.14
647
91
8
14.8
18.5
15.1
3.71
1.00
0.95
25
24
9
29.5
32.1
30.2
1.72
1.00
0.84
325
274
10
43.9
46.5
45.2
0.99
0.98
0.67
628
422
11
58
61.2
60.4
0.57
0.89
0.43
678
292
12
70.6
75.9
75.5
0.26
0.63
0.15
714
109
8
17.2
17.2
17.2
3.23
1.00
0.96
278
265
9
32.2
32.3
32.2
1.59
1.00
0.84
528
444
10
47.2
47.3
47.3
0.92
0.97
0.66
625
413
11
62.1
62.3
62.2
0.53
0.88
0.41
891
366
12
76.9
77.3
77.2
0.23
0.59
0.13
928
120
322
Table 1b: West Orientation
Day/
Month
Hour
Sol.Alt
VSA
OHR
Incid.
Ang
gvalue
Gcosvalue
SMS
sol.rad
(W/m2)
(W/m2)
13
86.2
87.8
0.04
87.8
0.14
0.01
344
2
14
72.5
72.7
0.31
72.8
0.71
0.21
372
78
15
57.6
57.7
0.63
57.7
0.92
0.49
505
249
16
42.7
42.7
1.08
42.8
0.98
0.72
567
409
17
27.7
27.7
1.90
27.7
1.00
0.88
242
213
18
12.7
12.7
4.44
12.7
1.00
0.98
72
70
13
72.5
85.2
0.08
85.4
0.26
0.02
505
11
14
64.3
70.4
0.36
71.3
0.74
0.24
708
168
15
52
55.7
0.68
57.5
0.93
0.50
572
285
16
38.5
40.9
1.16
44.0
0.98
0.71
508
359
17
24.6
26.1
2.04
31.7
1.00
0.85
392
332
18
10.5
11.1
5.08
22.2
1.00
0.93
128
118
13
82.8
83.9
0.11
83.9
0.33
0.03
722
25
14
68.6
68.9
0.39
68.9
0.79
0.28
442
125
15
53.8
53.9
0.73
54.0
0.95
0.56
211
118
16
38.8
38.8
1.24
38.9
0.99
0.77
489
377
17
23.9
23.9
2.26
24.0
1.00
0.91
86
79
18
8.9
8.9
6.38
9.0
1.00
0.99
31
30
13
74.4
82.0
0.14
82.2
0.41
0.05
808
44
14
63.5
66.8
0.43
67.5
0.81
0.31
625
194
15
49.9
51.7
0.79
52.8
0.95
0.58
189
109
16
35.6
36.6
1.35
38.3
0.99
0.78
305
238
17
21.1
21.6
2.53
24.3
1.00
0.91
133
121
18
6.9
7.0
8.11
12.9
1.00
0.98
44
43
2103
2105
2409
2010
Qsol
Table 1c: North orientation
Day/
Month
Hour
Sol.Alt
VSA
OHR
Incid.Ang
gvalue
Gcosvalue
2206
9
32
55.0
0.70
68.3
0.80
0.35
SMS
sol.rad
(W/m2)
353
10
45.2
63.0
0.51
68.9
0.79
0.33
442
147
11
57.4
67.2
0.42
69.3
0.78
0.32
405
131
12
66.8
69.1
0.38
69.5
0.78
0.32
714
226
13
69.3
69.6
0.37
69.6
0.78
0.31
650
205
14
62.7
68.4
0.40
69.4
0.78
0.32
450
143
15
51.6
65.5
0.46
69.1
0.79
0.33
394
129
16
38.8
59.7
0.58
68.5
0.80
0.34
336
114
17
25.3
48.6
0.88
67.9
0.81
0.35
164
58
Qsol
(W/m2)
122
323
Table 1d: South orientation
Day/
Month
Hour
Sol.Alt
VSA
OHR
Incid.Ang
gvalue
Gcosvalue
2112
9
29.9
49.60
0.85
64.90
0.80
0.34
SMS
sol.rad
(W/m2)
242
10
42.6
57.35
0.64
64.30
0.81
0.35
414
146
11
53.7
61.29
0.55
63.81
0.82
0.36
739
267
12
61.6
63.12
0.51
63.53
0.82
0.37
605
222
13
63.1
63.41
0.50
63.49
0.82
0.37
822
302
14
57.4
62.29
0.53
63.74
0.82
0.36
608
220
15
47.1
59.15
0.60
64.05
0.81
0.36
380
135
16
34.9
53.17
0.75
64.63
0.80
0.34
342
118
17
21.8
41.67
1.12
65.34
0.79
0.33
247
81
Sol.Alt: Solar altitude
OHR : Overhang ratio
VSA : Vertical shadow angle
Incid. Ang: Incident angle
Qsol
(W/m2)
82
SMS sol.rad : Global solar radiation at Subang Meteorological Station (Kuala
Lumpur)
Qsol
: Solar gain due to direct solar radiation through window (W/m2)
4.0 Discussion of Results
The shading depth depends on the required period of the day, where the solar
transmission is high. Assuming the building is occupied from 09:00 AM-17:00PM
and this period can be accepted as the maximum shading is required. Since the
working period is asymmetrical with respect to solar path, critical hours of solar
radiation transmission for each orientation differed. The lowest horizontal shadow
angle (HSA -2.30) is selected from all cardinal orientations to determine the shading
length. Depth of the device is given as a proportion to the window height, (1.82
meter or 6 feet). This dimensionless ratio; external horizontal shading depth to
window glazing height, is defined as ‘overhang ratio’ (OHR).
The following procedure was used to determine the overhang ratio or the
projection factor:
324
1. Determine the critical overheating period of the day, depending on the
orientation of the fenestration. E.g. east 9:00- 12:00 hours, west 13:00- 17:00 hours,
north and south between 9:00 AM and 17.00 PM hours.
2. From the tables (1a, 1b, 1c & 1d) maximum GCos values were identified
for respective orientations.
3. Compare the solar radiation intensities obtain for the correspondence
GCos values at (2).
4. Select the highest solar intensity and the correspondence GCos value and
the correspondence overhang ratio.
4.1 East and West Orientation
Impact of solar radiation incidence on the east façade is critical from 09:0012:00 hours and 13:00-17:00 hours for the west oriented facades. Beyond this limit
the building itself give shade as the sun position is behind the respective facades.
Window angle dependent g-values and GCos-values are high (>0.9) for east
orientation in the morning hours with lowest solar altitude angles and gradually
decreased when sun reaches toward noon position. This implies that between 8:00
and 9:00 hours in the morning, most of the incident radiation transmits through the
fenestration system (more than 90%). However, solar gain due to direct solar
radiation incidence on the vertical surface is low between 8:00 and 9:00 hours
compared to higher solar altitude. Vise-versa, although there is high intensity of
global solar radiation (> 600 W/m2) around noon the fraction of radiation transmitted
is lower (less than 40%) than at low solar altitude solar positions. Among all the
months, January, February and March (table 2) indicated a high g-value (>0.9) and
GCos (>0.8) values for east orientation. This implies that over 90% of g0-value was
transmitted into the building. Also, it could be stated as 10% of solar radiation
transmittance was reduced from g0-value for that respective solar altitude and
azimuth angles. Correspondence overhang ratios for all three days were indicated as
1.74, 1.72 & 1.59 for January, February and March respectively. But the direct solar
gain is high on March 21st, compared to January and February. This indicates that
only overhang ratio of 1.59 is required to terminate maximum amount of direct solar
radiation impinging on the east façade compared to overhang ratios at other low solar
325
altitude angles. This is about 8% reduction compared to the overhang ratio at lowest
solar altitude (1.74). Therefore, it can be assumed that an external horizontal shading
device with an overhang ratio 1.6 (~1.59) as optimum depth for east facing
fenestration. The lowest overhang ratio of less than 0.2 were reported on April, May,
June, August, September, October, November and December at 12.00 noon, for east
facing fenestration. The overhang ratios for fenestration on east façade range from
0.13 to 1.74 during critical hours (9:00-12:00).
Similarly, for west orientation a high g-value (>0.9) and GCos-values (>0.9)
are indicated for the month of September and October at 17:00 hours (table 2). Also
the correspondence overhang ratios were 2.26 and 2.53 which suggested a very deep
horizontal overhang. But on these two days and at the particular hour (17:00), the
direct solar gain is very low. From all the months March and May indicated high
direct solar gain on the west façade. Hence, the results indicated an overhang ratio of
between 2.04 and 1.90 is sufficient to eliminate maximum amount of direct solar
radiation incident on the west façade during the critical hour (17:00) of the
overheated period. The overhang ratio range varies from >0.1 to >2.53 for west
orientation.
Table 2: Summary of maximum g-value and GCos-value obtain for East and West
orientations.
Orientation/
Day/Month
Hour
Sol.Alt
Sol.
Azi
VSA
OHR
Incid.
Ang
gvalue
GCosvalue
Qsol
(W/m2)
E-2801
9
28
112.7
30.0
1.74
35.5
0.99
0.81
367
E-2302
9
29.5
103.4
30.2
1.72
32.1
1.00
0.84
274
E-2103
9
32.2
92
32.2
1.59
32.3
1.00
0.84
444
W-2103
17
27.7
268.4
27.7
1.90
27.7
1.00
0.88
213
W-2105
17
24.6
290.6
26.1
2.04
31.7
1.00
0.85
332
W-2409
17
23.9
267.9
23.9
2.26
24.0
1.00
0.91
79
W-2010
17
21.1
257.6
21.6
2.53
24.3
1.00
0.91
121
This implies that considering the glass solar radiation transmittance or the gvalue, GCos-value and the solar gain due to direct solar radiation incident on the
glazing are important factor in determining the solar shading depth.
326
4.2 North and South Orientation
The g-value and GCos value for North and South indicated lower values than
east and west orientations. During the month of May, June and July high g-value
(>0.7) and Gcos-values (>0.2, >0.3 &>0.2 respectively) were obtained for north
orientation. Month of June indicated high values than other months, (Table C.3).
Hence the GCos value is never higher than 0.4, meaning that the window orientation
itself reduces the incident radiation by 60% during the month of June. Evaluating gvalues for the date 22 June, at 09.00 hrs and 17.00 hours (>0.8) indicated higher than
other values. But a constant value (>0.7) is indicated during the shading period,
09.00-17.00. This implies that the solar radiation transmittance is symmetrical during
the maximum shading period.
Direct solar gain through south window were obtained on January, February,
March, September, October, November and December. Among these months
November, December and January obtained a high g-value (>0.8) and GCos-values
(>0.3) than other months. As in north orientation, GCos-value is never exceeding 0.4.
Thus orientation of the window itself reduces the intensity of the incident radiation
by 60% during the months where the impact of solar radiation is maximum. Month
of December indicated a highest g and Gcos values for south orientation and values
remain constant (g>0.8, GCos>0.34) throughout the required shading period. Note
that during the month of June and December the sun position is in the north solstice
and south solstice respectively.
Table 3: Summary of maximum g-value and GCos-value obtain for North and South
orientations.
Orientation/
Day/month
Hour
Sol.Alt
Sol.Azi
VSA
OHR
Incid.
Ang
gvalue
Gcosvalue
Qsol
(W/m2)
N-2206
9
32
64.1
55.0
0.70
68.3
0.80
0.35
122
N-2206
17
25.3
294.6
48.6
0.88
67.9
0.81
0.35
58
S-2112
11
53.7
138.2
61.29
0.55
63.81
0.82
0.36
267
S-2112
13
63.1
189.4
63.41
0.50
63.49
0.82
0.37
302
Projection factor differs from a minimum >0.1 to a maximum >0.8 for north
orientation, while range for south orientation is >0.2 to >1.2. But as for the north and
327
south orientation maximum g-value and Gcos values and their corresponding
overhang ratios were shown in table 3. According to the above table C.3, best options
of overhang ratios for north and south are respectively 0.8>OHR>0.7 and
0.6>OHR>0.5.
5.0 Conclusion
The results showed that window’s solar angle dependent properties and its
geometrical relationship to the direct solar radiation provide information to make
meaningful hypothesis about the external overhang depths. Comparison between the
window properties and the amount of solar energy transmitted, enable to predict
more realistic shading hypothesis than shading device calculations based on incident
angle only. It can be argued that, the obtained values can be defined as optimum
geometry of a shading device, compared to the direct solar radiation transmittance.
The above results suggested optimum overhang ratio of 1.6 (~1.59) for east
orientation, overhang ratio between 1.90 and 2.04 for west orientation, overhang
ratio between 0.8 and 0.7 for north orientation and between 0.6-0.5 for south
orientation. These optimum values were obtained for the building occupied period
that is from 9:00 am in the morning to 17:00 pm in the evening.
A design method to define the optimum solar shading geometry was
presented. Compared to shading mask method to define shading geometry, this
method provide additional information on intensity of solar radiation, window solar
angle dependent property and the geometrical relationship to the direct solar
radiation. These additional information assists to determine the critical overheated
periods affecting on a building façade at a given location and orientation. However,
energy simulations need to be carried out to justify the shading hypothesis obtained
from this experiment.
Another benefit of this method is that it gives a series of options of different
shading strategies internal or external, to decide based on shading device gcos-value
(or solar heat gain coefficient-SHGC) for different orientations. For example, a
328
shading device (internal or external) with gcos-value with 0.4>gcos>0.3 on south
window can be used to get maximum protection from solar heat gains.
The present study was conducted only considering the effect of direct solar
radiation. This may give more reasonable results under clear sky conditions.
However, considering the diffuse component might give more precise information on
the total heat transmittance. Further, in this study, the solar radiation calculations
were based on data obtained for horizontal surface. Data obtained on vertical surface
will provide more accurate results on overheating period and on shading geometry.
Reference
ASHRAE (1993) ASHRAE Fundamentals Handbook (SI), American Society of
Heating, Refrigerating and Air-conditioning Engineers, Inc. Atlanta
Dubois, Marie- Claude (2000) "A Method to define shading devices considering the
ideal total solar energy transmittance". Eurosun 2000 conference, June 19-22,
Copenhagen, Denmark.
Kuhun, Tilmann E; Bühler, Christopher and Platzer, Werner J (2000) "Evaluation of
overheating protection with sun-shading systems". Solar Energy,69(1-6): 5974.
Roos, A and Karlsson, B (1998) “Optical and thermal characterization of multiple
glazed windows with low u-values”. Solar Energy, 52(4):315-325
Stephenson, D.G (1965) “Equations for solar heat gain through windows”. Solar
Energy; 9(2):81-6
329
330
331
332
333
334
335
336
337
338
APPENDIX E2: DIRECT & DIFFUSED INCIDENT SOLAR RADIATION AND
TRANSMITTED HEAT GAIN DATA
Date
21st March
22nd June
24th September
22nd December
Date
21st March
22nd June
24th September
22nd December
Hour
9:00
12:00
15:00
17:00
9:00
12:00
15:00
17:00
9:00
12:00
15:00
17:00
9:00
12:00
15:00
17:00
Direct Solar Radiation Incident on Window (W/m2)
East Orientation
Overhang Ratio
0
0.4
0.6
0.8
1
1.4
285.26 210.55 173.36 135.85
98.66
23.96
157.60
0.00
0.00
0.00
0.00
0.00
0.00
0.00
0.00
0.00
0.00
0.00
0.00
0.00
0.00
0.00
0.00
0.00
115.36
81.01
63.67
46.65
29.31
0.00
31.20
0.00
0.00
0.00
0.00
0.00
0.00
0.00
0.00
0.00
0.00
0.00
0.00
0.00
0.00
0.00
0.00
0.00
107.17
76.28
60.83
45.39
29.94
0.00
110.32
0.00
0.00
0.00
0.00
0.00
0.00
0.00
0.00
0.00
0.00
0.00
0.00
0.00
0.00
0.00
0.00
0.00
502.74 354.92 280.84 207.09 133.01
9.77
128.60
0.00
0.00
0.00
0.00
0.00
0.00
0.00
0.00
0.00
0.00
0.00
0.00
0.00
0.00
0.00
0.00
0.00
Hour
9:00
12:00
15:00
17:00
9:00
12:00
15:00
17:00
9:00
12:00
15:00
17:00
9:00
12:00
15:00
17:00
Direct Solar Radiation Incident on Window (W/m2)
West Orientation
Overhang Ratio
0
0.4
0.6
0.8
1
0.00
0.00
0.00
0.00
0.00
0.00
0.00
0.00
0.00
0.00
311.42
106.85
4.73
0.00
0.00
421.11
329.38
283.68
237.66
191.64
0.00
0.00
0.00
0.00
0.00
0.00
0.00
0.00
0.00
0.00
168.32
65.25
13.55
0.00
0.00
87.94
69.97
60.83
52.01
42.87
0.00
0.00
0.00
0.00
0.00
0.00
0.00
0.00
0.00
0.00
77.85
30.57
6.93
0.00
0.00
204.56
163.59
143.10
122.61
102.12
0.00
0.00
0.00
0.00
0.00
0.00
0.00
0.00
0.00
0.00
119.78
54.53
21.75
0.00
0.00
120.09
99.60
89.52
79.12
68.71
APPENDIX E2: cont.
Date
Hour
Direct Solar Radiation on Window (W/m2)
1.6
0.00
0.00
0.00
0.00
0.00
0.00
0.00
0.00
0.00
0.00
0.00
0.00
9.77
0.00
0.00
0.00
1.4
0.00
0.00
0.00
99.92
0.00
0.00
0.00
24.90
0.00
0.00
0.00
61.46
0.00
0.00
0.00
48.86
1.6
0.00
0.00
0.00
54.21
0.00
0.00
0.00
16.39
0.00
0.00
0.00
40.98
0.00
0.00
0.00
39.72
339
North Orientation
Overhang Ratio
0
0.4
21st March
22nd June
24th September
22nd December
Date
21st March
22nd June
24th September
22nd December
9:00
12:00
15:00
17:00
9:00
12:00
15:00
17:00
9:00
12:00
15:00
17:00
9:00
12:00
15:00
17:00
Hour
9:00
12:00
15:00
17:00
9:00
12:00
15:00
17:00
9:00
12:00
15:00
17:00
9:00
12:00
15:00
17:00
0.6
0.8
1
1.4
6.30
0.00
0.95
9.46
6.30
0.00
0.95
9.46
No Direct Solar radiation
56.11
60.52
118.20
40.35
19.86
0.00
0.95
21.12
6.30
0.00
0.95
14.18
6.30
0.00
0.95
9.46
No Direct Solar radiation
No Direct Solar radiation
Direct Solar Radiation on Window (W/m2)
South Orientation
Overhang Ratio
0
0.4
0.6
0.8
9.77
1.58
1.58
1.58
37.82
0.00
0.00
0.00
26.79
0.00
0.00
0.00
11.98
2.52
2.52
2.52
1
1.58
0.00
0.00
2.52
1.4
1.58
0.00
0.00
2.52
0.00
0.00
0.00
0.00
33.41
0.00
1.89
20.17
0.00
0.00
0.00
0.00
33.41
0.00
1.89
18.91
No Direct Solar radiation
5.99
46.65
7.56
7.56
282.42
345.14
100.55
60.52
0.00
0.00
0.00
0.00
133.01
45.70
28.37
39.08
0.00
0.00
0.00
0.00
70.60
0.00
1.89
30.89
APPENDIX E2 cont.
0.00
0.00
0.00
0.00
33.41
0.00
1.89
24.59
340
Date
21st March
22nd June
24th September
22nd December
Date
21st March
22nd June
24th September
22nd December
Hour
9:00
12:00
15:00
17:00
9:00
12:00
15:00
17:00
9:00
12:00
15:00
17:00
9:00
12:00
15:00
17:00
Hour
9:00
12:00
15:00
17:00
9:00
12:00
15:00
17:00
9:00
12:00
15:00
17:00
9:00
12:00
15:00
17:00
Diffused Solar Radiation Incident on Window (W/m2)
East Orientation
Overhang Ratio
0
0.4
0.6
0.8
1
1.4
1.6
189.75
136.48
120.09
107.80
98.97
87.00
82.58
211.81
173.04
161.07
152.24
145.62
136.80
133.64
177.46
144.68
134.28
126.71
121.35
113.79
110.95
132.07
104.02
95.19
88.57
83.84
77.54
75.33
214.97
153.19
133.64
119.46
109.37
94.88
89.83
177.77
133.64
119.78
109.37
102.12
91.72
88.26
132.70
104.65
95.82
89.52
84.79
78.17
75.96
57.05
42.55
38.14
34.67
32.47
29.00
28.05
171.47
122.61
107.48
96.14
88.26
76.91
72.81
191.64
158.86
148.46
140.89
135.54
127.97
125.45
155.08
117.25
105.28
96.77
90.46
81.64
78.48
100.23
76.59
69.03
63.67
59.57
53.90
52.01
95.51
76.28
69.97
65.56
62.41
58.00
56.42
178.72
147.83
138.06
131.12
126.08
118.83
116.62
119.15
92.04
83.53
77.22
72.81
66.51
64.30
76.28
57.37
51.38
46.96
43.81
39.72
38.14
Diffused Solar Radiation Incident on Window (W/m2)
West Orientation
Overhang Ratio
0
0.4
0.6
0.8
1
1.4
87.31
68.40
62.41
58.31
55.16
50.75
170.21
145.31
137.43
131.75
127.66
121.98
280.84
213.39
192.27
176.83
165.80
150.35
328.44
234.82
205.51
184.08
168.63
146.88
109.37
82.90
74.39
68.40
63.99
57.68
152.24
116.31
105.28
97.08
91.09
82.90
208.98
155.71
138.69
126.71
117.57
105.28
126.08
88.57
76.91
68.40
62.09
53.58
96.45
72.81
65.25
59.89
55.79
50.43
164.22
140.58
133.33
127.97
123.87
118.52
223.16
162.64
143.73
129.86
119.78
105.59
266.97
187.54
162.64
144.36
131.44
112.84
66.19
56.42
53.58
51.38
49.80
47.60
156.34
133.01
125.76
120.41
116.31
110.95
171.47
126.71
112.84
102.76
95.19
84.79
161.07
113.79
98.97
88.26
80.38
69.66
1.6
49.17
119.78
144.68
139.32
55.48
79.75
100.86
50.43
48.54
116.62
100.86
106.54
46.65
109.06
81.32
65.56
341
APPENDIX E2 cont.
Date
21st March
22nd June
24th September
22nd December
Date
21st March
22nd June
24th September
22nd December
Hour
9:00
12:00
15:00
17:00
9:00
12:00
15:00
17:00
9:00
12:00
15:00
17:00
9:00
12:00
15:00
17:00
Hour
9:00
12:00
15:00
17:00
9:00
12:00
15:00
17:00
9:00
12:00
15:00
17:00
9:00
12:00
15:00
17:00
Diffused Solar Radiation on Window (W/m2)
North Orientation
Overhang Ratio
0
0.4
0.6
0.8
98.66
75.96
69.03
63.67
181.24
152.56
143.73
137.11
194.16
155.71
143.73
134.91
153.50
118.20
107.17
98.97
161.07
116.94
103.39
93.30
197.63
146.57
130.81
119.15
186.60
140.58
126.08
115.68
88.57
63.67
55.79
50.12
104.65
78.17
69.66
63.67
170.21
144.68
136.48
130.81
164.85
123.56
110.64
101.18
117.25
87.63
78.48
71.55
66.19
56.42
53.58
51.38
150.67
129.23
122.30
117.57
119.15
92.04
83.53
77.22
76.28
57.37
51.38
46.96
Diffused Solar Radiation on Window (W/m2)
South Orientation
Overhang Ratio
0
0.4
0.6
0.8
102.12
78.48
70.92
65.56
191.33
159.18
149.40
142.16
202.99
161.70
148.77
139.32
158.86
121.67
110.32
101.81
109.69
82.90
74.70
68.40
147.51
113.16
102.44
94.56
133.01
104.96
96.14
89.52
57.05
42.55
38.14
34.99
108.43
80.69
72.18
65.88
181.87
152.24
143.10
136.17
171.15
127.97
114.42
104.33
123.24
91.72
81.95
74.70
82.58
67.45
62.72
59.26
211.50
169.58
156.65
147.20
163.27
121.35
108.11
98.66
118.83
85.73
75.33
67.77
1
1.4
54.84
125.76
119.78
85.10
75.96
98.97
97.40
40.35
53.27
120.41
85.10
59.89
47.60
109.06
66.51
39.72
1
1.4
55.79
129.23
122.61
87.00
57.68
81.01
78.48
29.31
54.84
124.50
87.31
62.09
53.27
130.49
81.95
54.53
59.89
132.38
128.60
93.30
86.05
110.64
108.11
46.02
59.26
126.40
94.56
66.82
49.80
114.10
72.81
43.81
61.46
136.80
132.38
95.51
63.99
88.89
85.10
32.47
61.15
131.44
97.08
69.34
56.74
140.26
91.72
62.41
342
APPENDIX E2 cont.
Date
21st March
22nd June
24th September
22nd December
Date
21st March
22nd June
24th September
22nd December
Hour
9:00
12:00
15:00
17:00
9:00
12:00
15:00
17:00
9:00
12:00
15:00
17:00
9:00
12:00
15:00
17:00
Hour
9:00
12:00
15:00
17:00
9:00
12:00
15:00
17:00
9:00
12:00
15:00
17:00
9:00
12:00
15:00
17:00
Transmitted Heat Gain through Window (W/m2)
East Orientation
Overhang Ratio
0
0.4
0.6
0.8
1
392.10
286.92
242.09
200.77
162.06
247.45
135.29
125.78
118.85
113.82
137.94
112.37
104.37
98.53
94.29
103.97
81.82
74.87
69.80
66.13
267.47
189.51
159.64
133.88
111.19
152.69
104.01
93.19
85.29
79.56
102.73
81.01
74.21
69.25
65.66
44.27
33.11
29.61
27.06
25.21
225.75
161.21
136.11
114.25
94.79
195.20
124.44
116.40
110.53
106.28
120.32
90.89
81.69
74.96
70.08
79.01
60.18
54.29
50.00
46.88
501.71
361.10
293.63
227.44
162.19
196.35
116.49
108.90
103.36
99.35
93.18
71.88
65.22
60.35
56.82
59.19
44.52
39.93
36.58
34.15
1.4
88.76
106.81
88.38
60.99
74.94
71.56
60.63
22.63
60.38
100.34
63.27
42.53
53.76
93.74
51.90
30.75
1.6
64.80
104.33
86.29
59.18
70.98
68.74
58.86
21.72
57.26
98.24
60.87
40.99
52.48
91.77
50.16
29.56
Transmitted Solar Heat Gain through Window (W/m2)
West Orientation
Overhang Ratio
0
0.4
0.6
0.8
1
1.4
68.47
53.63
48.98
45.59
43.14
39.70
132.99
113.52
107.43
102.98
99.76
95.25
462.78
249.77
152.96
137.25
128.61
116.52
619.59
467.53
405.24
349.17
297.74
201.89
86.17
65.13
58.55
53.74
50.26
45.39
118.48
90.59
81.87
75.50
70.88
64.43
291.09
170.19
117.47
97.60
90.77
81.22
172.05
127.78
111.08
96.82
84.39
62.43
75.53
56.93
51.11
46.87
43.79
39.49
129.00
110.39
104.57
100.32
97.25
92.94
236.34
151.13
117.29
100.84
93.04
82.13
385.92
288.39
251.31
219.50
191.65
141.92
52.13
44.52
42.15
40.41
39.15
37.39
122.86
104.54
98.81
94.62
91.59
87.35
228.70
142.00
105.23
80.21
74.43
66.35
226.33
172.43
152.30
135.27
120.53
95.20
1.6
38.49
93.66
112.26
156.43
43.67
62.15
77.85
52.92
37.97
91.42
78.29
119.19
36.77
85.86
63.50
84.40
343
APPENDIX E2 cont.
Date
21st March
22nd June
24th September
22nd December
Date
21st March
22nd June
24th September
22nd December
Hour
9:00
12:00
15:00
17:00
9:00
12:00
15:00
17:00
9:00
12:00
15:00
17:00
9:00
12:00
15:00
17:00
Hour
9:00
12:00
15:00
17:00
9:00
12:00
15:00
17:00
9:00
12:00
15:00
17:00
9:00
12:00
15:00
17:00
Transmitted Solar Heat Gain through Window (W/m2)
North Orientation
Overhang Ratio
0
0.4
0.6
0.8
1
77.42
59.59
54.02
49.95
46.99
141.59
119.25
112.26
107.16
103.46
150.99
121.07
111.71
104.87
99.92
120.74
93.02
84.32
77.97
73.37
166.04
106.01
85.86
77.96
72.23
194.73
114.18
101.76
92.69
86.12
223.27
108.95
97.85
89.74
83.87
96.73
64.07
53.18
45.43
42.23
81.89
61.17
54.69
49.96
46.53
133.44
113.32
107.02
102.43
99.10
127.70
95.81
85.84
78.55
73.27
92.45
69.13
61.85
56.53
52.68
52.13
44.52
42.15
40.41
39.15
118.39
101.56
96.30
92.45
89.66
93.18
71.88
65.22
60.35
56.82
59.19
44.52
39.93
36.58
34.15
Transmitted Solar Heat Gain through Window (W/m2)
South Orientation
Overhang Ratio
0
0.4
0.6
0.8
1
81.32
61.64
55.78
51.49
48.39
156.07
124.48
116.68
110.98
106.85
161.57
125.34
115.29
107.95
102.63
126.52
96.36
87.23
80.52
75.66
86.54
65.39
58.78
53.94
50.44
114.79
88.14
79.80
73.72
69.30
103.07
81.23
74.40
69.42
65.80
44.37
33.17
29.67
27.10
25.25
86.08
64.28
57.45
52.47
48.86
152.56
129.37
122.12
116.83
112.99
134.28
100.67
90.15
82.47
76.91
98.03
73.20
65.42
59.75
55.63
274.81
152.00
101.80
71.42
69.44
427.51
168.39
123.43
115.92
110.49
202.35
115.86
85.83
78.35
72.94
136.04
94.85
80.81
70.38
63.00
1.4
42.87
98.29
92.99
66.94
64.24
76.94
75.66
37.75
41.74
94.44
65.88
47.30
37.39
85.77
51.90
30.75
1.4
44.05
101.08
95.20
68.88
45.55
63.14
60.75
22.66
43.82
107.64
69.13
49.89
66.67
102.89
65.36
56.05
344
345
346
347
348
349
350