THERMAL PERFORMANCE OF BANGLADESH
TRADITIONAL HOUSE
DURING WINTER AND SUMMER SEASONS
RUMANA RASHID
UNIVERSITI TEKNOLOGI MALAYSIA
THERMAL PERFORMANCE OF BANGLADESH
TRADITIONAL HOUSE
DURING WINTER AND SUMMER SEASONS
RUMANA RASHID
A thesis submitted in fulfillment of the
requirement for the award of the degree of
Master of Architecture
Faculty of Built Environment
Universiti Teknologi Malaysia
JUNE 2008
iii
To:
My Beloved Father, Mother
and
My Husband, Son and Daughter.
iv
ACKNOWLEDGEMENT
In the name of Allah, the most Gracious, the most Merciful, for giving me the
determination and will to complete this study.
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 Dr. Dilshan Remaz
Ossen for his critics advice, guidance, motivation and friendship. Without their
continued support and interest, this thesis would not have been the same as presented
here.
A special thanks to Mdm. Halimah Yahya for her assistance in obtaining the
required weather data and also for her friendship and support.
My sincere gratitude also goes to those who have provided assistance in
many ways at various occasions: Dr. M.A. Mukhtadir, Deen of the Department of
Architecture, AUST, Dr. Jasmin Ara, Head of the Department of Architecture,
AUST, Assoc. Prof. Mahfil Ali, Assoc. Prof. Mahboob Mallick and my colleagues of
AUST.
My heartiest and utmost gratitude goes to my dear father, mother and sisters
and Brother in law for their patience, sacrifices, understanding, constant concern,
moral support and prayers during the course of my study.
I would like to say special thanks to Shazib, Shakir, Fahim and Rokon from
AUST and Shamima and Sazib from FEA for their support and help during my thesis.
v
I would like to say special thanks to Shakil Mahabob for his help to buy the
thermal data logger.
Finally I would like to say utmost special thanks to my husband for his
continuous support, inspiration and encouragement towards the completion of the
thesis.
vi
ABSTRACT
Bangladesh traditional house is a typical example of dwelling which
encapsulates the socio- cultural values of the country and traditional form. Currently,
urban development in Bangladesh is threatening the traditional houses. Study on
performance of traditional houses in Bangladesh is also rare compared to researches
done on the contemporary or modern houses. Thus, the aim of this study is to
evaluate the thermal performance of Bangladesh traditional houses in the context of
Dhaka during summer and winter seasons. Quantitative method is used to measure
the thermal performances.
The field survey was conducted using thermal data
loggers. A set of thermal data loggers were installed in selected Bangladesh
traditional houses in Dhaka to record the air temperature of the indoor, outdoor and
upper spaces. Data collection was carried out for duration of two months in winter
and four months in summer. The research found that the traditional Bangladesh
house is comfortable in both summer and winter seasons. It also noted that the
thermal performance of traditional house depended on the different percentage of
window openings in the upper space during both seasons. During the winter time as
expected, closing the window openings throughout the day provided good thermal
indoor environment.
However, during summer seasons, closing the window
openings of the upper space in the day time and opening them at night resulted in
better thermal comfort indoor. This finding is important as it is contrary to the
conventional belief of the occupants that opening their windows in the upper spaces
during daytime in the summer will provide cooler indoor temperature. This study
concludes that the use of upper spaces in Bangladesh traditional houses have
significant impact on the overall indoor thermal performance. Thus, modern houses
should consider employing this upper space to achieve thermal comfort.
vii
ABSTRAK
Rumah tradisional Bangladesh merupakan contoh kediaman yang tipikal
dimana ia mengambil kira nilai budaya negara dan bentuk tradisionalnya. Pada masa
ini, pembangunan bandar di Bangladesh telah mengancam rumah tradisional. Kajian
tentang prestasi rumah tradisional pula adalah amat kurang jika dibandingkan dengan
kajian ke atas rumah moden atau kontemporari. Oleh itu, kajian ini bertujuan untuk
menilai prestasi terma rumah tradisional dalam konteks Dhaka semasa musim panas
dan dingin menggunakan metod kuantitatif. Kerja lapangan dijalankan menggunakan
pengumpul data terma. Satu set pengumpul data terma digunakan bagi pengukuran
dalaman dan luaran rumah serta dalam ruang atas atau juga dipanggil loteng.
Pengumpulan data dibuat selama dua bulan dalam musim dingin dan empat bulan
dalam musim panas. Kajian ini mendapati rumah tradisional Bangladesh ini adalah
selesa bagi kedua-dua musim panas dan dingin. Kajian juga mendapati prestasi terma
rumah tradisional ini bergantung kepada perbezaan peratusan bukaan tingkap di
loteng untuk kedua-dua musim. Seperti dijangkakan, menutup tingkap sepanjang hari
dalam musim dingin menghasilkan lingkungan terma dalaman yang lebih baik.
Sebaliknya, sewaktu musim panas, menutup bukaan tingkap pada siang hari dan
membukanya pada waktu malam memberikan keselesaan terma dalaman yang baik.
Dapatan ini adalah penting kerana ia adalah berlainan dengan kepercayaan biasa
pengguna yang beranggapan membuka tingkap di ruang atas atau loteng pada waktu
siang akan memberikan suhu dalaman yang lebih sejuk. Kajian ini menyimpulkan
bahawa kegunaan loteng memberikan kesan yang jelas terhadap prestasi terma
dalaman secara keseluruhan.
Oleh itu, rumah moden perlu mengambil kira
penggunaan loteng ini untuk mencapai keselesaan terma dalaman.
viii
TABLE OF CONTENTS
CHAPTER
1
TITLE
PAGE
Thesis Title
i
Declaration
ii
Dedication
iii
Acknowledgement
iv
Abstract (English)
vi
Abstrak (Bahasa Melayu)
vii
Table of Contents
viii
List of Tables
xv
List of Figures
xviii
List of Abbreviations
xxiii
List of Symbols
xxiv
List of Appendices
xxv
GENERAL INTRODUCTION
1
1.1 Introduction
1
1.2 Statement of the Problem
4
1.3 Research Hypothesis
4
1.4 Research Questions
5
1.5 Research Gap
6
1.6 Research Objective
7
1.7 Scope and Limitations
7
1.8 Significance of the Research
9
ix
1.9
2
Research Position
10
1.10 Thesis Organization
10
1.11 Conclusion
12
TRADITIONAL HOUSE IN BANGLADESH
13
2.1
13
Introduction
2.2 History of Traditional house
2.3
2.4
14
2.2.1 Transformation of Houses Through Ages
17
Use of Local available Material
18
2.3.1 Kutcha House
18
2.3.2 Semi-Pucca house
19
Different region According to Climatic Zone have
19
Different Type of Traditional House
2.5
2.6
Description of Different Types of Traditional Houses
22
2.5.1 Mud House
22
2.5.2 Bamboo House
27
2.5.3 Timber House
31
2.5.4 Stilts house
32
Significant common feature of traditional house in
37
Bangladesh
2.6.1 Arrangement of the traditional in Bangladesh
37
2.6.2 Upper space
37
2.6.3 Traditional houses are rebuiltable structure
41
2.6.4 Windows of traditional house
41
2.6.5 Elevated house
42
2.7
Upper space design from user demand
43
2.8
The Reason of Selection of the Stilts House for this
44
Research
2.9
Conclusion
47
x
3
4
CLIMATE OF BANGLADESH
48
3.1
48
Introduction
3.2 Climate of Bangladesh: Classification and Outline
49
3.3
Climatic Regions of Bangladesh
52
3.3.1 South-eastern Zone
54
3.3.2 North-eastern Zone
54
3.3.3 Northern part of the northern region
54
3.3.4 North-western Zone
54
3.3.5 Western Zone
54
3.3.6 South-western Zone
55
3.3.7 South-central Zone
55
3.4
Urban Climatic Elements of Dhaka City
55
3.5
Temperature
56
3.6
Relative Humidity
59
3.7
Rainfall
61
3.8
Wind speed and direction
63
3.9 Solar Radiation
66
3.10 Conclusion
70
PREVIOUS STUDY ON CLIMATE OF DHAKA CITY
71
4.1
Historical Background of Dhaka City
71
4.2
The Impact of Urbanization on Microclimate of Dhaka
72
4.3
Historical Studies on Climate
74
4.4
Previous Studies on Micro-Climates in Dhaka City
76
4.5
Climatic Comfort
80
4.6
Definition and Concepts of Comfort
81
4.7 Previous Research on Indoor Comfort
82
4.8
The Indoor Comfort Zone
86
4.8.1 Summer Comfort Zone
88
4.9
The Outdoor Comfort
89
xi
4.10
5
6
4.9.1 Air temperature
89
4.9.2 Radiation
90
4.9.3 Relative Humidity
90
4.9.4 Airflow
90
4.9.5 Comfort Zone for Outdoors
91
Conclusion
92
METHODOLOGY
93
5.1
Introduction
93
5.2
Objective of the Field Study
95
5.3
Historical background of the Test House
95
5.4
Selection of particular Test House
97
5.5 Description of the Test House
97
5.6
100
Instrumentation
5.7 Installation of the Data Loggers
102
5.8
Methodology of Data Collection
103
5.9
Impact of the surrounding
107
5.10 Conclusion
109
PERFORMANCE OF TRADITIONAL HOUSE AT
110
DHAKA CITY
6.1
Introduction
110
6.2
Comparative study of Field measurement and
110
Meteorological data.
6.3
6.2.1 Winter season
111
6.2.2 Summer season
112
Field Study
113
6.4 Field Study Result : Comparative study of Air
114
Temperature of the Test House to justify role of upper
space
6.4.1
Winter Season
114
xii
6.4.1.1 Analyzing air temperature during Himalayan
115
cold wind flow period for selected Days (12
and 13 January)
6.4.1.2 Analyzing air temperature during Termination
118
of Himalayan cold wind flow period for
selected Days (18 and 19 January)
6.4.1.3 Analyzing air temperature for selected days
120
under common weather condition for winter
season (20and 21 January, 10 February and 27
and 28 February)
6.4.2 Summer Season
6.4.2.1 Field study result of 7th March and 8th March
122
123
without any opening in upper space during
summer season
6.4.2.2 Field study result from 1st April to 2nd April
126
with 25% (percent) window opening in upper
space
6.4.2.3 Field study result of 7th and 8th May, 14th and
128
15th June and 19th and 20th June with, 75 %
(percent) opening in upper space in summer
season
6.5
Performance Evaluation of Daily Day Maximum and
131
Minimum Temperature with respect to Thermal Comfort
Temperature Range
6.5.1 Evaluate Maximum and Minimum Air Temperature
131
in Winter Season
6.5.2 Evaluate Maximum and minimum temperature in
133
Summer Season
6.6
Comparative Study of Temperature difference between
Indoor maximum, Outdoor maximum and Upper
maximum for selected days.
135
xiii
6.7 Comparative study of winter and summer season at 6.00am
136
and 6.00 pm
6.7.1 Winter Season with 0% window opening in upper
137
space
6.7.2 Summer Season with 0% window opening in upper
138
space
6.7.3 Summer Season with 75% window opening in upper
140
space
6.8
Study of Comfort Zone Analysis of Winter and Summer
142
season
6.8.1 Evaluation of Indoor Comfort during Summer Season
6.9
143
6.8.2 Evaluation of Indoor Comfort during Winter Season
145
Role of Upper space during Winter and Summer seasons
146
6.9.1 Winter season during Himalayan Cold Wind flow
146
6.9.2 Winter season during common Weather Condition
147
6.9.3 Summer season during 0% opening in Upper space
149
6.9.4 Summer season during 25%and 75% opening in
150
Upper space
7
6.10 Conclusion
151
CONCLUSION
153
7.1
153
Review of Thesis Objectives and Research Questions
7.2 Thesis Conclusion
7.2.1
The vital role of upper space with diurnal variation
of ambient environment
7.2.2
The thermal performance of traditional house in
154
154
155
Bangladesh which is influenced by the upper space
during winter and summer season with different
percentage of window opening
7.2.3
The traditional house in context of dense Dhaka city
158
still comfortable for summer and winter
7.3
Research result
159
xiv
7.4
Suggestions for Further Research
BIBLIOGRAPHY
160
161
APPENDICES
A
Equipment Details
166
B
Data From HOBO Data Logger
171
C
Bangladesh Meteorological Department Weather Data
184
D
Per minute temperature Data
187
E
Previous Study
192
F
Publications
198
xv
LIST OF TABLES
TABLE NO.
TITLE
PAGE
2.1
Name and description of different types of traditional houses
15
2.2
State of houses by materials of walls and roofs in Dhaka city
45
3.1
Classification of the seasons and weather condition of
52
Bangladesh
3.2
Air temperature profile of Dhaka city year 1950-1980
56
3.3
Air temperature profile of Dhaka city year 1981-1990
57
3.4
Air temperature profile of Dhaka city year 1991-2000
57
3.5
Air temperature profile of Dhaka City year 2002-2006
57
3.6
Monthly and annual mean relative humidity of Dhaka city
60
for 1950 –2006
3.7
Monthly and annual mean rainfall of Dhaka city for 1950 –
62
2006
3.8
Average reduction factors for wind in different location
64
3.9
Monthly mean prevailing wind speed and direction of Dhaka
64
city
3.10
Monthly global solar radiation between BUET and
67
Meteorological Department of Dhaka
3.11
Monthly global solar radiation, Diffuse radiation and Direct
68
radiation of Dhaka city
4.1
Temperature difference between Dhaka city and Tangail
(rural area)
73
xvi
4.2
Changes in mean monthly temperature and humidity of
74
Dhaka City
4.3
Karmokar et. al’s research methodology and findings
77
4.4
Hossain et al’s research methodology and findings
78
4.5
Hossain et al’s research methodology and findings
79
4.6
Khaleque et. al’s research methodology and findings
80
4.7
Comparative study of various thermal indices and calculated
83
their range of application
4.8
Discomfort index for Dhaka
84
4.9
Previous study of Indoor comfort temperatures
85
5.1
The seasons and months of Bangladesh with climatic
104
condition
5.2
Tabular output method of climatic data for the test room of
106
the traditional house
6.1
The season and the percentage of the window opening in
113
upper space
6.2
General weather condition of Dhaka in winter season (2007)
115
6.3
Air temperature difference during Himalayan cold wind flow
116
period for selected Days (12 and 13 January)
6.4
Air temperature difference during termination of Himalayan
118
cold wind flow period for selected Days (18 and 19 January)
6.5
Air temperature difference under common condition during
120
rest of winter period for selected days of January and
February
6.6
Common weather condition of Dhaka in summer according
123
to BMD
6.7
Air temperature difference, under common condition during
summer for selected days without window opening in the
upper space
124
xvii
6.8
Air temperature difference under common condition during
126
summer periods for selected days with 25 % window
opening in the upper space in the upper space.
6.9
Air temperature difference under general condition during
129
summer period for selected days with 75 % window Opening
in the upper space
6.10
Tabular format of indoor temperature within comfort range
134
for summer season
6.11
Selected days temperature difference between 6am to 6pm
138
6.12
Selected days temperature difference at 6am and 6pm
139
6.13
Selected days temperature difference at 6am and 6pm
141
6.14
Tabular format of duration time and hour of indoor space
142
thermal comfort environment
6.15
Relation between temperature difference of indoor, outdoor
152
and upper space with different percentage of window
opening in upper space
7.1
Tabular format of minimum and maximum temperature in
156
both seasons of indoor, outdoor and upper space
7.2
Daily Maximum and minimum temperature difference with
157
different percentage of upper space window opening in
winter and summer season
7.3
The tabular format of thermal comfort duration in indoor of
traditional house
158
xviii
LIST OF FIGURES
FIGURE
NO
1.1
TITLE
Dense Dhaka city skylines during day and clouded night and
PAGE
2
traditional stilts house
1.2
Variation in energy consumption at different time of the year in
3
Dhaka city
1.3
Cross section of the test house
5
1.4
Diagram of research position
10
1.5
The flow of research process and thesis structure
10
2.1
The traditional house in rural areas in Bangladesh
14
2.2
The traditional house sharing introvert court yard
16
2.3
Changes of the traditional house through ages
17
2.4
The Kutcha House and Semi-Pucca house in Bangladesh
18
2.5
The different type of traditional houses of different region in
20
Bangladesh
2.6
The Mud house
23
2.7
The different types of construction of Mud house walls
24
2.8
The construction of C.I. sheet roofs with wooden ceilings and
25
wall construction in mud house
2.9
Protection from insects and vermin in mud house
26
2.10
The common bamboo house in Bangladesh
27
2.11
The section of the flood prone area’s bamboo house in
27
Bangladesh
2.12
Framework of the bamboo house and entry way to upper space
28
2.13
Cross bracing of bamboo structural frame
29
xix
2.14
Upper space ventilation of bamboo house and wall gap from
30
floor
2.15
The timber house with extended verandah.
31
2.16
The timber house exterior and interior with raised floor
31
2.17
The stilts house exteriors from the courtyard
32
2.18
The plinth of the stilts house during construction and after
33
construction
2.19
The structural framework of the stilts house during construction
34
2.20
The upper space and interior of living space
34
2.21
The construction method of Stilts House Roof pitch
35
2.22
The construction of rain water gutter
36
2.23
Arrangement of traditional house
37
2.24
The ladder of upper space entry and window opening of the
38
upper space
2.25
Upper space in a stilts house during construction
39
2.26
Upper space in a wooden house
39
2.27
Upper space in a bamboo house
39
2.28
Upper space wall opening in Stilts house
40
2.29
Upper space ventilation of Bamboo house and Mud house
40
2.30
Easy repairing of the traditional house
41
2.31
Windows of the traditional house in Bangladesh
42
2.32
Elevated floor of the traditional house in Bangladesh
42
2.33
The entry of upper space and use of upper space as store
43
2.34
The entry way to upper space of the traditional house in section
43
2.35
The flood condition of 2005 in Dhaka city and suburban area
44
2.36
The physical conditions of traditional house at different areas in
46
Dhaka city
3.1
Location of Bangladesh in the World Map
49
3.2
Regional Map showing the radar coverage
50
3.3
The climate sub zone of Bangladesh
53
3.4
Monthly Mean Min and Max temperature from 1950 to 2006
58
3.5
Monthly Relative Humidity from 1950 to 2006
61
xx
3.6
The Rainfall Profile of Dhaka City
63
3.7
The Wind speed Profile of Dhaka City
65
3.8
Monthly Mean solar radiation over Dhaka and clearness index
68
3.9
Monthly Mean cloud cover Dhaka city
69
4.1
Temperature and humidity changes of Dhaka city
75
4.2
Olgyay’s Bio-climatic chat and Adaptation of comfort zone in
87
warm climate
4.3
Summer comfort zone for Bangladesh
88
4.4
Summer comfort zone graph
91
5.1
Location of Test house area (Gulshan) in Dhaka city Map
94
5.2
Physical condition of Test house area (Gulshan) in Dhaka city
94
5.3
Traditional house (test house) in dense Gulshan area
96
5.4
Same type of traditional house in rural area Maowa
96
5.5
Birds eye view of the surroundings of the Test House
98
5.6
Plan of the Test House
98
5.7
Interior of the Test House
99
5.8
Thermal Data Logger position in upper space and placement of
100
external sensor
5.9
Thermal Data Logger position in upper space (left) and windows
101
of upper space (right)
5.10
Thermal Data Logger position in indoor, upper space and
102
outdoor in test house plan and section
5.11
Use of thermal data logger and sensors
102
5.12
Window opening 25% of the upper space during construction
106
(right top) and 75% window opening (left bottom)
5.13
Position of the Data loggers Ti = Temp indoor, To= Temp
107
outdoor, Tu = Temp upper space
5.14
The site and surroundings of the test house and distance from
other houses
108
xxi
6.1
Profile of daily average temperature of meteorological office
111
data and field study data of same days in winter season
6.2
Profile of daily average temperature of meteorological office
112
data and field study data of same days in summer season
6.3
Profile of indoor, outdoor and upper space air temperature of the
117
test house during Himalayan cold wind flow period (12 and 13
January)
6.4
Profile of indoor, outdoor and upper space air temperature of the
119
test house during termination of Himalayan cold wind flow
period (18 and 19 January)
6.5
Profile of indoor, outdoor and upper air temperature in common
121
weather condition of the test room without window opening in
the upper during winter season for selected days
6.6
Profile of indoor, outdoor and upper air temperature of the
124
indoor living without window opening in the upper space in
selected days in month of March (7 and 8 March)
6.7
Profile of indoor, outdoor and upper air temperature of the
127
indoor living space with window opening in the upper space in
summer season (1st and 2nd April)
6.8
Profile of indoor, outdoor and upper air temperature of the test
130
room with 75% window opening in the upper space
6.9
Profile of maximum and minimum air temperature of indoor,
132
outdoor and upper space from field study during winter season
without opening in the upper space (10-27 January and 9, 10, 27
& 28 February, 2007)
6.10
Profile of maximum and minimum temperature of indoor,
133
outdoor and upper air temperature of the test house
6.11
Profile of maximum temperature difference of indoor, outdoor
135
and upper space air temperature of the test house in the selected
days
6.12
Profile of temperature of indoor, outdoor and upper space air
temperature of the test house at 27th and 28th February, 2007
137
xxii
6.13
Profile of temperature of indoor, outdoor and upper air
139
temperature of the test house at 7th and 8th March, 2007
6.14
Profile of temperature of indoor, outdoor and upper air
140
temperature of the test house at 19th and 20th June, 2007
6.15
Plotting of the indoor temperature and the indoor relative
143
humidity of the indoor living space within summer comfort zone
6.16
Plotting of the indoor space temperature and indoor the relative
144
humidity of the indoor living space of the test house, within
summer comfort zone according month (March, April, May and
June)
6.17
Plotting of the indoor temperature and indoor relative humidity
145
of the indoor living space within winter comfort zone (January
and February)
6.18
Heat flow pattern, during day and night when Himalayan cold
147
wind flow occur in winter (Ti= indoor temperature, Tu= upper
space temperature, To= outdoor temperature)
6.19
Heat flow pattern during day and night in general weather
148
condition in winter
6.20
Heat flow pattern during day and night 0% opening condition in
149
summer
6.21
Heat flow pattern during day and night condition in summer
150
xxiii
LIST OF ABBREVIATIONS
ASHRAE
-
American Society of Heating, Refrigerating and Air
Conditioning Engineers
BMD
-
Bangladesh Meteorological Department
BST
-
Bangladesh Standard Time
BUET
-
Bangladesh University of Engineering and Technology
CV
-
Comfort Vote
D.I
-
Discomfort Index
ET
-
Effective Temperature
GMT
-
Greenwich Mean Time
TTC
-
Thermal Time Constant
xxiv
LIST OF SYMBOLS
%
-
Percentage
°K
-
Degree Kelvin
Max
Maximum
Min
Minimum
ºC
-
Degree Centigrade
ºF
-
Degree Fahrenheit
Rh
-
Relative Humidity
Td
-
Dry bulb temperature (0C)
Tg
Ti
Globe Temperature
-
Tn
Indoor temperature (0C)
Neutral Temperature
To
-
Outdoor temperature (0C)
Tu
-
Upper space temperature (0C)
Tw
-
Wet bulb temperature (0C)
CHAPTER 1
GENERAL INTRODUCTION
1.1
Introduction
Traditional House represents the heritage of Bangladesh and also reflects
traditional forms and values, fundamental to the culture of the people of the country.
It possesses distinct characteristics with regards to planning, use of materials and
location. Like urban architecture, traditional house is also subject to change but in
Bangladesh the traditional houses have clung to tradition. It has not really changed
until recently. For centuries traditional houses has been using locally available
materials. It is only from the late 19th century that the traditional houses began to
change in the use of materials. Traditional architecture in Bangladesh was largely
built without formally trained professionals. Buildings were built by construction
workers. The full planning concept has been developed by the people according to
needs. The traditional house has been changed along with time to fulfill the demand
of the user. At the same time planning concept remains constant. The different
kinds of houses were developed in different climatic regions of Bangladesh such as
mud houses, bamboo houses, stilts houses and timber houses. The stilts house was
selected for this research study. The reason will be discussed at the end of this
chapter.
Dhaka, being the capital of Bangladesh is the most important city of the
country. In addition to housing the central administrative and institutional facilities,
the city now accommodates nearly 6 million people (Population Census 2006) on an
2
area of 815 square kilometers. The above two figures indicate density of about 8251
persons per square kilometer. A considerable portion of land of the city is now
under the control of law-enforcing authorities and that in fact results in higher
densities in habitable area. According to Climatologists, the growth of high-rise
buildings at close proximity and the use of vehicles have changed the general city
climate and have created numerous micro-climates in some areas. It is obvious that
such changed microclimates can affect the climates inside the adjacent traditional
house.
Figure 1.1
Dense Dhaka city skylines during day and clouded night (lower left)
and traditional stilts house (lower right).
The roof is the main element of the house that has much exposure to the sun
and therefore gains solar radiation. The impact of solar radiation affects the thermal
behavior of roof more than any other part of the house especially in tropical
countries (Mallick, 1993). In Bangladesh, most of the roofs are exposed to direct
solar radiation, and which elevates the indoor temperature above the local indoor
3
comfort level (24ºC to 32ºC by Mallick, 1993) in summer seasons (Abul Mukim
Mridha, 2002). Mechanical cooling is a very expensive (per unit 3.5 taka) option. In
such a context, developing passive means of the solar control is important for
comfortable living and higher productivity during hot seasons of the year.
Traditional houses are designed by the owners according to demands and are based
on low investment, rebuiltable structure and use of local materials. In Bangladesh
modern house, reinforced concrete roof is very common but uncomfortable for living
at night (Abul Mukim, 2002). Mechanical cooling is a very expensive option.
In terms of energy used, the distribution of the critical hours has considerable
importance particularly during the summer months when the consumption of energy
(electricity) is expected to increase. The hours between 10am and 5pm the energy
consumption is at its peak (figure 1.2; Sabbir Ahmed 1995).
Figure 1.2
Variation in energy consumption at different time of the year in
Dhaka city.
On the other hand, from user experience, traditional houses of Bangladesh
are less hot during the daytime, but it becomes comfortable within a short time after
sunset. Therefore, the question arises on how the traditional house of Bangladesh
can afford to control natural climate for achieving thermal comfort environment in
indoor space. This is the main issue that influences this research.
4
1.2
Statement of the Problem
In Bangladesh the temperature difference between rural and urban area is 4ºC
to 5ºC (Mallick, 1993) because of the amount of hard surface along with the high
outdoor temperature. Traditional houses are based on low investment and high
maintenance and the general construction materials are mud, bamboo, thatch wood
C.I. sheets etc.
These houses are extensively protected from effects of solar
radiation by trees, open surroundings allowing easy cross ventilation, which produce
its own microclimate, often include good solution of climatic comfort problems. For
technological limitations and the always-overriding considerations of safety, some of
these solutions must be considered ingenious (Koenigsberger et al, 1973). But in
cities due to heavy concentration of the surrounding built environment this is not
always successfully achieved. Most of the activities are performed outdoors. So
indoor comfort is mainly important during night time (Mallick, 1993).
1.3
Research Hypothesis
The hypothesis of this study is that the upper space of the traditional house in
Bangladesh will achieve the following:
1. The thermal performance of traditional house in Bangladesh is influenced
by the upper space during winter and summer seasons.
2. By controlling the wall openings of the upper space of the traditional
house, indoor occupant space can achieve thermal comfort environment
within the context of the dense Dhaka city.
5
Heat gain
Figure 1.3
Heat loss
Cross-section of the test house
The window openings of the upper space play a vital role for the thermal
environment of the traditional house.
1.4
Research Questions
The following questions will be addressed in this thesis:
1. How upper space plays a vital role with diurnal variation of ambient
environment?
2. What is the thermal performance of traditional house in Bangladesh which is
influenced by the upper space during winter and summer seasons with
different percentage of window openings?
3.
Does the traditional house provide thermal comfort in context of dense
environment of Dhaka city?
6
1.5
Research Gap
Very few studies were done about thermal performance and thermal comfort
in respect to Dhaka city. The thermal performance of the operable roof insulation
with special reference to Dhaka done by Abul Mukim Muzzammel Haque Mridha,
(2002). He recommended that operable roof insulation at 450mm and 300mm height
above the roof confirms that roof insulation at relatively higher height performance
better than lower height. The factors for thermal comfort in residential high rise in
Dhaka city is done by Bijon Behari Sarma, (2002) and suggested that the roof of the
top floor be rendered heat-registrant by using suitable means.
There is no specific research done to study the thermal performance of upper
space of traditional house in Bangladesh.
Most of the research’s are on the
contemporary architecture in Bangladesh.
Previously some attempts were made to improve roof insulation. A study by
Imamuddin et al (1993) and others using hollow blocks plastered over concrete roof
has found differences of about 4-5ºC between the ceiling surfaces of such an
insulated slab as compared to a standard concrete slab for flat roofs. The difference
was more for inclined roofs. The difference in room temperature was however less,
a maximum of 2 ºC. But the study is incomplete, as it did not record temperature
data for 24 hours.
Another study was conducted by F.H. Mallick (1993) by using earthen pots
laid over concrete roof. The room temperature of insulated roof was found to be 2.53.4ºC lower in comparison without insulated roof at around 3pm.
It is evident from both experiments that using fixed insulation on the roof top,
day time temperature can be reduced to a lower level but these methods reduce the
potential of radiant cooling as in both cases the indoor temperature is higher than the
outdoor.
These studies suggest suitable means or insulation for modern building roofs.
However, the traditional house with double layer roof sections (upper space),
7
appears to have solved the thermal environment of the traditional house. Therefore,
this thesis attempts to focus on the thermal performance of the roof section in
traditional house with different window openings in respect to the impact of indoor
temperature during different seasons in Dhaka city.
1.6
Research Objective
The aim of the study is to investigate the thermal performance in Bangladesh
traditional house roof section in the context of an uncomfortable dense environment
of Dhaka city with the following objectives:
1. To evaluate the thermal performance of traditional house.
2. To study the influence of upper space of the traditional house on the indoor
thermal performance during winter and summer periods.
3. To study the effect of window openings at upper space, on the room thermal
performance.
4. To evaluate the potential role of upper space with difference percentage of
window openings and how they influence the indoor thermal environment.
1.7
Scope and Limitations
1. The scope of research is to investigate the thermal performance of the
traditional roof section and the changes that occurs in the indoor thermal
environment with diurnal variation of the room during summer and winter
season.
2. The main limitation was during the field investigation from 10th January to
20th June. Some degree of uncertainty was present in the data collection by
thermal data Logger such as -69ºC to 289ºC from 27th January to 8th
February and 11th February to 25th February. For this reason, the above
mentioned period data was not analyzed in this research.
8
3. The following days were chosen for hourly analysis
Season
Winter
Summer
Month
Selected Dates
January
12, 13, 18 ,19 20 & 21
February
10, 11, 27 & 28
March
7&8
April
1&2
May
7&8
June
14, 15,19 & 20
4. They were only short winter periods (December to February) and there was
delay in (9th Jan) getting the equipment from the supplier to start the field
measurement.
The thermal data logger also recorded some degree of
uncertainty during the winter period. For these reasons, this research did not
manage to analyze the thermal performance of the traditional house with
different percentage of wall openings in the upper space.
5. Due to the limitations of the thermal data logger, the field measurements and
data collection were possible only in one house (test house).
6. Wind flow also can have an effect on thermal performances of house but it is
not considered in this experiment because of field study site is a highly dense
area at Gulshan. Highest wind speed occurs in April 2.9 m/s and lowest in
November 1.3 m/s. Because of the surroundings, effective cross ventilation
was not achievable in the test house. There are other parameters effecting the
thermal comfort, for e.g. air velocity, clothing, sky conditions and metabolic
heat production, which are not considered within this research work
7. The thermal comfort aspect was mainly dealt based on indoor to outdoor
temperature differences.
8. Above these opportunities and constraints, research on the thermal
performance of the upper space in Bangladesh traditional house with
9
reference to dense Dhaka city was carried out and described in the following
chapters.
1.8
Significance of the Research
The significance of the research depends on the understanding of the thermal
performance of traditional house in Bangladesh in the context of dense Dhaka city.
This research further establishes a number of casual relationships between
the traditional houses design component with various micro-climatic factors. Hence
by adopting the appropriate design strategy, modern houses can be effectively
designed towards sustainable urban environments.
This research study helps to develop the practical design guidelines for the
modern house designers.
The micro-climatic study of the traditional houses
conducted in dense Dhaka city, indicate the difference that exists within the larger
context of the urban climate.
10
1.9
Research Position
Performance of indoor thermal comfort
Temperature Differences
Performance of Upper space
Percentage of Openings in
Upper space for ventilation
Traditional
house is
comfortable
during
Winter and
Summer
Upper space
Figure 1.4
1.10
Diagram of research position.
Thesis Structure
Thesis Problem
Literature Review
Traditional house of
Bangladesh
Chapter 2
Climate of
Bangladesh
Chapter 3
Previous study on
Climate of Dhaka
City
Chapter 4
Figure 1.5
Methodology of
Data collection
Chapter 5
Results and Analysis
Chapter 6
Conclusion
Chapter 7
The flow of research process and thesis structure.
11
The thesis is organized into seven chapters as summarized below.
Chapter one introduces the main issue of this research. This chapter also
introduces the statement of the problem, objectives of the study, scope and limitation
of the study and significance of the research. The research gap, research questions
and research hypothesis and the overall thesis structure are also presented in this
chapter.
Chapter two introduces the typology of the traditional houses of Bangladesh.
This chapter describes the various types of the traditional houses of Bangladesh
according to materials used, history and transformation of the traditional houses.
The upper space (Attic) is also discussed in detail.
Chapter three presents the classification of climate and climatic region of
Bangladesh. This chapter vastly explains the urban climatic elements of Dhaka city
such as temperature, rain fall, humidity, wind speed etc.
Chapter four introduces the historical background of the Dhaka City. The
previous study of climate, climatic comfort, indoor comfort, summer comfort zone,
outdoor comfort, summer comfort zone will also be explained.
Environmental
criteria and comfort vote are also described in this chapter.
Chapter five introduces the methodology of this research. It describes the
objective of the methodology and description of the selected traditional house in
Dhaka city.
Instrumentation, installation of thermal data logger (Hobo) and
placement of logger and methodology of data collection are also mentioned here.
Chapter six presents the results and analysis of this research. It describes
the temperature difference of outdoor, indoor and upper space with the change of
seasons and also with different percentage of window openings of the upper space.
Temperature difference between Bangladesh Meteorological Department and field
study data are also explained here.
12
Chapter seven presents the overall review of the thesis objectives and
research questions, followed by the concluding remarks of the major findings of the
experiment. Finally, it suggests further works to complement the thesis findings.
1.11
Conclusion
What has been discussed in this chapter is a brief introduction of the subjects
that might be necessary for the understanding of this research. It included, a brief
about the hypothesis and objective of the study, background information on
Bangladesh and Dhaka city, the context regarding traditional houses of Bangladesh
in Dhaka city and past investigations on thermal comfort etc.
Finally a brief
discussion on the research structure for this study has also been included in this
chapter.
CHAPTER 2
TRADITIONAL HOUSE IN BANGLADESH
2.1
Introduction
Traditional housing is located vastly in rural areas, as confirmed in a study by
Koenigberger et al (1973). Traditional housing is designed by the owner and based
on low investment, local materials, combined with the assistance of relations, friends
and neighbors.
Traditional house reflects cultural heritage of peoples and also
encapsulate traditional forms values.
The practice of drawing on traditional
architecture to form contemporary design has been promoted by many theorists and
distinguished architects such as Hasan Fathy (Steebe, 1988).
Among other
advantages they claim, is the benefit to be derived from centuries of experience in
adapting form and material selection to achieve comfort in relation to the local
climate. In Bangladesh urban development is currently threatening to the traditional
houses almost total destruction. Contemporary dwellings which are characterless,
thermally inefficient and expensive to run, are replacing traditional village housing
which is light weight, cool, made of renewable materials and able to be built largely
by sweat equity (Kevin mecartery,2006). So it is essential for Bangladesh to take
some sensitive approach to solve this problem. But before taking this attempt it is
essential to know about the tradition houses in Bangladesh. This chapter presents
the structure, construction and design, arrangement, and important feature of the
traditional house according to typology. Traditional houses are influenced by the
local available materials, climate depended and economic ability of the people.
According to the comfort demand, most of the time traditional houses are designed
14
by the owners. From history it has been shown that the owner of the traditional
house are changing and rebuilding the design of traditional houses deserve its ability
to maintain comfortable conditions for longer periods than the contemporary houses
(Kevin mecartery,2006).
Figure 2.1:
2.2
The traditional house in rural areas in Bangladesh
History of the Traditional Housing
Housing has been changing its forms and styles throughout its history in
response to socio-economic forces as well as climatic conditions and geographic
locations of Bangladesh. Settlements in Bangladesh territory initially took place in
the highlands of southeastern areas covered with forestations that gave natural
protection from floods, tides of the rivers and sea and cyclones. Gradually, with
increase in population the settlements have spread throughout the areas. The growth
of population ultimately came out as the single major factor for spreading the
settlements all over Bengal, which almost entirely remained rural until the close of
the 17th century. Development of small townships in ancient Bengal by the kings
and their representatives at various places had once introduced a group of special
types of houses constructed mostly within fort structures.
These houses had
residence of the owners at the center and rooms for service and support personnel
alongside the boundary walls. Archeological excavations have discovered some of
15
such houses in different parts of Bangladesh and almost all of them were built with
mud bricks.
The house forms, building styles and materials used in construction had
significant variations in different areas of Bengal. Perhaps the only thing in common
was the clustering of houses in particular places forming a para, a few of which
grouped together to form a village (Masud Hassan chowdury, 2005). Historically,
bamboo had been the most important building material for housing in Bangladesh.
Even today bamboo is widely used and as in the past, bamboo is good in making the
fences for rooms and as pillars or crossbars to support the roofs. Other materials
used in rural areas in making fences for rooms or houses include canes, jute sticks,
corrugated iron sheets, wood, mud or mud bricks. The village houses are mostly
thatches and the materials are used to cover their tops includes khad (straw from
dried paddy or wheat plants), san or ‘ulukhad’ (reed), kash (tail grass) and golpata
(leaves of a special species of small tree, growing mostly in marshland).
The
relatively stable structures use corrugated iron sheets stretched on a flat frame or
supported on a triangle shaped bamboo or wooden base. Houses built with mud
walls elevated areas in Dhaka, Barisal and Chittagong divisions are also in
abundance.
Structurally, the traditional rural houses in Bangladesh may be grouped into
seven types (Masud Hassan chowdury, 2005).
Table 2.1:
Name and description of different types of traditional houses.
Name
Description of structural arrangement
Chouchala
Four rooms on four raised sides and a ‘uthan’ or open space in the
middle.
Duichala bandh ghar
The house and all its rooms fenced within one boundary.
House with eight roofs, four over the main building and four over
the verandas attached on each side.
House constructed on elevated platform.
House of two large rooms on two separate platforms and an open
place between them.
Susthita ghar
House surrounded by verandas on all four sides; and house of the
tribal people.
Britighar
Atchala
Postaghar
16
Figure 2.2:
The traditional house sharing introvert court yard.
The common arrangement of rural traditional house is by locating in units
built together, shaving introverted courtyards plan, which shut out all males except
immediate members of the household. They share ponds and wells from which they
draw their water for bathing, washing clothes and pans as well as vegetables, meat
and fish for cooking. As there is often no sewage facilities at all, toilets are almost
always located at a distant place from the main living areas, the waste being disposed
on to moving waterways or sunken trenches. Kitchens are also separate from the
main house. Straws and bamboos are also the most popular roofing materials with
corrugated iron sheeting over wooden beams trailing second preference. The lack of
electrification in villages necessitates the use of natural ventilation to its fullest
extent. There is no doubt that the modern designer has a lot to learn from traditional
or vernacular houses, as there have emerged from an effort to satisfy the social and
17
physical needs, of the inhabitants of a region from time immemorial (Sadat Ullah
Khan, 2005)
2.2.1
Transformation of Houses Through Ages
In Dhaka, as elsewhere in the world, houses have suffered from changes due
to new needs, changes in people’s attitudes towards living, introduction of new
materials and technology, changes in climate conditions, changes in the attitudes and
policies of the government etc. The city of Dhaka, at present stands as a megapolis
and capital of independent state Bangladesh and was initiated as an abode of some
businessmen, with some traditional residential and business houses. The houses
were constructed with timber posts having sloping thatched roofs above and thatched
or mud walls around.
Figure 2.3:
Changes of the traditional house through ages
Day by day those materials were gradually replaced by brick walls, burnttiles roofs, corrugated iron (C.I.) sheet walls and roofs and finally reinforced cement
concrete (R.C.C.) framed and R.C.C roof structures. Changes happened also in
planning and organizations. Earlier there was no dearth of land and various
structures for accommodations were placed far apart for ensuring privacy and having
climatic privileges. The introductions of C.I. sheets and brick walls made closer
placing or even combine several spaces under the same roof possible.
The
replacement of slopped roofs by flat R.C.C roofs allowed for the concept of multiple
level living.
18
2.3
Use of Local available Materials
According to organic materials use, there are two types of traditional houses
in Bangladesh.
2.3.1
•
Kutcha House.
•
Semi-Pucca house.
Kutcha House.
The house is made of totally organic materials such as bamboo, mud, jute
stick and catkin grass, etc.
ƒ
Walls: Organic materials like jute stick, catkin grass, straw, bamboo mats,
etc. Split are bamboo framing. In some areas wall are made by earth.
ƒ
Foundation: Earthen plinths with bamboos or timber posts or elevated
wooden or bamboo floors.
ƒ
Roof: Thatch-rice, wheat or maize straw, catkin grass, etc with split
bamboo framing.
Organic
Materials
Inorganic
Materials
Kutcha House
Figure 2.4
Semi-Pucca House
The Kutcha House and Semi-Pucca house in Bangladesh.
19
2.3.2
Semi-Pucca House
The house is made of a mixture of materials such as steel house, wooden
house etc.
ƒ
Walls: Bamboo mats, CI sheet, Timber or bamboo framing. In some
areas wall are made of earth and sometimes part or full brick.
ƒ
Foundation: Earthen plinth; Brick perimeter wall with earth infill; Brick
and concrete are also used.
ƒ
2.4
Roof: CI sheet with timber or bamboo framing.
Different region According to Climatic Zone have Different Type of
Traditional House
The traditional house in rural areas of Bangladesh offers a fine example of
culture, region specific social product. (Dr.M.A. Muktadir et al, 1985). Bangladesh
is located in subtropical monsoon region. There are widespread differences in the
intensity of the seasons at different places of the country. On the basis of entire
climatic conditions, Bangladesh can be divided into the following seven distinct
climatic zones (described in the third chapter widely).
20
Figure 2.5
The different type of traditional houses of different region in
Bangladesh
According to climatic zone, different types of traditional houses were
developed in different zones. It also depends on the availability of materials and also
climatic disasters such as flood, drought, hailstorm, tornadoes etc. Climatic disaster
21
gives impact on the traditional houses. So in the hilly region mud houses, bamboo
houses are found, in low land where flood occurs there elevated stilts house is
popular. Barishal, Cox’s Bazar where bamboo is a less available, timber house are
built.
South-eastern zone (A) - In Chittagong traditional houses are usually made of
mud, bamboos, wood, catkin grass etc. In Sundarbans traditional hoses are elevated
wooden tribal houses. In Comilla, the houses usually use C.I. sheet and bamboo.
Mean temperature range is 13c to 32c, with heavy rainfall over 2,540 mm. it is a
flood affected area.
North-eastern zone (B) - This is the cloudiest part of Bangladesh. The higher
hills and mountains of the Chittagong sub-region can also be classified under this
zone. In Sylhet mud houses are very popular. Elevated wooden houses are also
found here due to slopes of the hilly area. Bamboo is also available here for
construction. Mean temperature range is 10c to 32c, with heavy rainfall over 3,340
mm. Flood effected area.
Northern part of the northern region (C)- The summer is dry, with a
scorching westerly wind; Very few areas are affected by floods in this zone. So
Mud houses are vastly developed in this zone and bamboo houses are also popular
here. Mean temperature range is 10c to 32c, with heavy rainfall between 2,000 to
3,000 mm.
North-western (D)-The lower rainfall makes this area both atmospherically
and pedologically drier. Mud house is popular here and two storied mud houses are
also constructed here. In Dinajpur rammed earth wall is a popular construction
method for houses. Floods seldom affect some areas in this zone. Mean temperature
range is 10c to 32c, with low rainfall 1,400 mm.
Western zone (E) - In summer, it is the hottest and driest of all climatic zones.
Bamboo house and mud house are available here. Some areas are affected by floods.
Mean maximum temperature is over 35c, with rainfall 1500 mm.
22
South-western zone (F)- Dew-fall is heavier than in Western zone. Here the
traditional houses are made of wooden frames, C.I. sheets and bamboo tribal stilts
houses are found here. Most of areas are affected by floods. Mean maximum
temperature is below 35c, with rainfall 1,500 to 1,800 mm.
South-central zone (G)- Here stilted houses are very popular as traditional
house. Mud houses, bamboo and wooden houses are also constructed in some areas.
Mean temperature is 11ºC in winter and summer 35.4ºC, with rainfall of 1,900 mm.
Dhaka city is included within this region.
2.5
Description of Different Type of Traditional Houses
In Bangladesh according to the use of materials the traditional houses are
broadly divided into four types. Those are as follows:
1. Mud house
2. Bamboo house
3. Timber house
4. Stilts house.
2.5.1
Mud House
Mud house is popular in the dry zone of Bangladesh. The earthen plinth is
extremely vulnerable and can get damaged even in low intensity floods, thus
requiring frequent maintenance. In moderate to high intensity floods, especially if
accompanied by currents, earthen plinths tend to get completely washed off and have
to be rebuilt. Compact monolithic earthen plinths are not stable. So it requires some
time for capping the plinth with cement may stabilize the earth. This is cheaper,
easier to construct and maintain. Complete stabilized earth plinth is more expensive
and harder to construct, but the results are more durable. Cement stabilization of the
typical earthen plinth can be carried out with a mixture of earth and cement. The
proportion of cement to be added depends on the nature of the soil.
23
Figure 2.6
The Mud house
Various types of wall are constructed according to regions. In monolithic
construction, floodwater can cause serious damage. Once the base gets affected, the
entire structure is liable to collapse, often rapidly. Earthen walls with an internal
framework are vulnerable. Even if the earth cover is washed away, the building
remains standing and can be repaired. For areas with heavy rainfall and flood, it is
essential for earthen houses to have an internal structural framework. Framework
can be of bamboo or timber, which should be treated against decay. Mud may be
used as plaster or daubing without serving as structural element. Adding cement to
the mud plaster stabilizes it and allows resisting erosion. Different types of internal
frame work of the mud wall are shown in figure 2.4
24
Construction of double layer bamboo framing in Mud house
Guideline for wattle-and-daub construction
Construction process for monolithic rammed earth wall
Figure 2.7
The different types of construction of Mud house walls.
It is usual to use double C.I. sheet roofs with wooden frameworks. The roof
is strong and well-built, in addition to the use of durable, water-resistant materials
and wind-resistant design. Fibrous thatching material, such as catkin grass, rice
straws, palm fronds, wheat, maize or sugarcane leaves need to be soaked in
preservative solution for 12 hours. Thatch is used over C.I sheets as a protection
from direct solar radiation.
25
Figure 2.8
The construction of C.I. sheet roofs with wooden ceilings and wall
construction in mud house.
The foundation plinth must be higher then the flood level. The house should
be built on raised homesteads with slightly sloping ground for drainage. The cost
because of cement stabilization may increase by more than 50% (ADPC,2005), but
its feasibility should not be seen only in apparent cost increase. It is still much less
expensive than pucca construction (brick and concrete) and greatly increases flood
resistance. Over the long term, cost savings would be realized due to reduced
maintenance and labor for regular repair of earthen houses, especially after floods.
Extended roof eaves should be used to protect earthen walls from rain.
Rainwater gutters should be used to discharge water away from the house. Added
benefit is collecting arsenic-free rainwater for domestic use.
Roof should be
supported on posts instead of earthen walls.
Basic principles for good ventilation should be followed such as exposing
roof spaces having accessible loft spaces and adequate windows oriented to facilitate
prevailing wind flow direction. Adequate ventilation is essential for earthen houses,
which otherwise leads to dampness that can weaken the structure.
26
Figure 2.9
Protection from insects and vermin in mud house.
Protection from insects and vermin is essential for mud houses. Various
insects, including worms, termites and ants, and also rodents and birds tend to
burrow into earthen walls and establish their habitats. This can weaken earthen
plinths and walls substantially. Cement-stabilized earthen construction deters insects
and rodents from burrowing and building habitats. Termite shields should be used if
walls are not load bearing and does not require connection to the plinth.
Earthen plinth and walls require regular maintenance, often plastered every
week, especially during the wet seasons.
Since women do this work, it is
unaccounted labor and places an extra demand on women who are often
overburdened with domestic tasks.
There are some limitations of mud house. Water is the greatest enemy of
earthen houses. Floodwater affects the typical earthen plinth, thus weakening the
base of walls. Combined with capillary rise of water into the walls, this can result in
collapse of the entire house.
27
2.5.2
Bamboo House
Bamboo is an easily growing organic material for houses of Bangladesh. So
bamboo is a popular material all over the country.
Figure 2.10
The common bamboo house in Bangladesh.
Cement stabilized earthen plinths are used in bamboo houses. Occasionally,
the houses are built with elevated bamboo frameworks and bamboo mats as plinths.
In some flood-prone areas, houses have a built-in wooden/ bamboo platform
(machan) normally used as storage space, but during flood serves as a raised refuge
area. This practice should be encouraged and promoted for wider replication.
Figure 2.11: The section of the flood prone area’s bamboo house in Bangladesh.
Stabilization of the typical earthen plinth can be carried out with a mixture of
earth and cement. The proportion of cement to be added depends on the nature of
the soil, which can easily be tested on site.
Capping the plinth with cement-
stabilized earth is cheaper, easier to construct and maintain. Complete stabilized
28
earth plinth is more expensive and harder to construct, but the results are more
durable.
Typically bamboo houses have bamboo mat walls with bamboo or timber
posts. Also organic materials like jute sticks, catkin grass are used. Flood with
strong currents can destroy wall panels, get washed away and may be partially or
complete lost, especially if the connections to posts are weak.
Figure 2.12: Frame work of the bamboo house and entry way to upper space.
Local treatment of the bamboo mat walls is done by bituminous, oil etc.
Simple chemical preservative treatment methods (dip diffusion method, internodal
injection method or hot and cold method) for increasing the longevity of organic
materials have been developed a long time ago. Cost can increase by 20-25%, but
can increase longevity by more than three or four times. Untreated, bamboo mat
walls do not last more than 4-5 years in outdoor conditions, but after treatment lasts
for 15-20 years (ADPC, 2005).
Typically, roofs in bamboo houses are made from catkin grass, rice wheat or
maize straws with usually bamboo and sometimes reed stalk framings. Thatching
materials can get detached and wash away. Secondary hazards often connected to
29
flood are heavy rainfall, which can cause damage. Strong winds can also blow away
thatching materials and damage frames. So in some regions C.I. sheet are also used
for roofs.
Figure 2.13: Cross bracing of bamboo structural frame.
To increase stability and wind- resistance of the structural frame of bambooframed houses, cross bracing with split bamboo sections should be done. If a house
becomes weakened at its base due to flood, cross bracing helps to keep the structure
stable. Split bamboo sections used for cross bracing should be treated with chemical
preservatives so that they do not decay easily and lose their strength. Instead of jute
or coir rope, nylon rope or good quality galvanized wire should be used for tying the
elements of the structural frame.
Concrete stump (katla) or if affordable, brick plinth should be used to support
bamboo posts. Resting bamboo walls on the plinth should be avoided. It is better to
30
have a small gap (around 1 inch) between wall bottom and floor to also prevent from
termite infestation.
Upper space ceiling is used as storage; it should allow ventilation and should
be accessible for maintenance. Adequate number and size of perforated bamboo mat
walls should be built oriented along the prevailing wind flow direction to allow cross
ventilation. Extended roof eaves are to be used to prevent direct wetting of walls
during rain.
Figure 2.14: Upper space ventilation of bamboo house and wall gap from floor
Rainwater gutters can be used to discharge water away from the house while
collecting arsenic-free rainwater. Houses should be built house on raised homestead
with slightly sloping ground for drainage.
31
2.5.3
Timber House
In southern regions close to the coast, bamboo is less widely grown and
timber is more in use in house construction. Good quality timber, such as garjan,
although in high demand, is generally expensive and imported from hilly areas and
does not grow in the floodplains. Low-income villagers can seldom afford it.
Figure 2.15: The timber house with extended verandah.
In timber houses cement stabilized plinth is used as a base. In some hilly
region elevated bamboo or wooden floor are used. There is a cabin under the floor
in private area that is used as a store in dry seasons. Local method for protecting the
base of bamboo/ timber posts by supporting on concrete stumps embedded into the
plinth or ground and connecting them by MS (mild steel) clamps locally known as
kaatla or shiri. It is possible to reduce cost by 10% by making the kaatla partially
hollow.
Space can be filled with sand/earth before placing in the ground and
strength is not compromised.
Figure 2.16: The timber house exterior and interior with raised floor.
32
Timber planks of best wood with wooden frames are used for walls. Some
traditional preservatives such as gubbing, oil, paint, bituminous etc. are used for
weather protection. For wall protection from the direct rainfall, timber plank on the
inside surface of the wall are used. Surface treatment such as painting with bitumen
can serve as waterproofing. If timber posts are used, they should not be buried into
the ground and instead should be supported on concrete stumps.
For roofing, the use of MS flat bar clamps (similar as in kaatla) for screwing
on to roof structure is evident. To prevent rust, the MS clamps can be painted with
molten bitumen. Upper space should be left exposed to allow better airflow and
ventilation with a good number of windows.
2.5.4 Stilts House
Typically stilts houses are raised on bamboo or timber stilts and have a floor
made of split bamboo sections or timber planks of good quality timber which is
generally expensive and rare in many areas. Stilted housing is usually prevalent in
areas that are relatively better off economically, or where timber is available locally,
especially if the floor and ceiling is made of timber planks and the walls are made of
C.I sheet. So stilts houses are popular in Dhaka and suburban areas of Dhaka. The
use of RC posts as stilts is becoming common in areas with a tradition of stilted
housing, substituting the typical timber and bamboo stilts.
Upper
space
Extended
C.I. sheet
roof
Elevated
floor
Figure 2.17: The stilts house exteriors from the courtyard
33
These have the advantage of being water resistant and hence more durable.
There are some examples of houses on stilts in some flood-prone regions and also
urban informal settlements are sometimes built on stilts on waterlogged land, which
are in low demand. Roadside shops are also quite often stilted and could serve as
examples for introduction in houses in flood-prone areas.
Elevated wooden plank floor are also used in stilts house. Parallel Dowa
Posta plinths are also used in stilts house. Brick perimeter walls locally known as
"Dowa-Posta", a brick perimeter wall around the typical earthen plinth can resists
erosion from the sides. If soil is too weak or loose, the foundation of the perimeter
wall should penetrate to sufficient depth, preferably with a spread footing. Since
very little load is imposed on the wall, the footing can be constructed with brick
without the need for a concrete footing. Minimum 1:4 cement-sand mixes should be
used. Soil cover on the foundation should be thoroughly compacted and should
preferably have plant or grassy cover to prevent scouring during flood. Infill should
be of cement-stabilized soil to prevent muddiness, settlement due to saturation and
loss of soil from bottom.
Figure 2.18: The plinth of the stilts house during construction and after
construction.
34
Figure 2.19: The structural framework of the stilts house during construction
Figure 2.20: The upper space and interior of living space.
The stilts house have an adequate upper space which have a ceiling of timber
planks and C.I sheet roof on the outside, which is known locally as upper space or
‘Dartala’. For the roof structure, wooden frames of 62.5mm X 75mm timber plank
section are used. MS or G.I roof structure can be made typically with 37.5 mm X
37.5 mm X 6.5 mm section in some area. Timber planks, those are used for framing
have been chemically treated properly for longer life. MS angle roof structures
should be paint with corrosion resistant paint (red oxide). Cross-bracing is used in
roof and ceiling, and also for openings of upper space. Openings are restricted in
size.
35
Upper space should be left exposed to allow better airflow and ventilation.
Adequate number and size of windows should be built, oriented along the prevailing
wind flow direction to allow cross ventilation.
Figure 2.21: The construction method of Stilts House Roof pitch.
Protection against wind-hazard contributes to the overall improvement of
housing in all regions. Four basic principles should be followed:
1. Roof pitch 30°- 40° to reduce effects of suction and uplift.
2. Hipped instead of gable roof. If gable, then ends should be tied down firmly
to rest of the structure. Lean-to should be avoided.
3. Overhangs greater than 0.75m vents in roof and masonry parapet should be
employed.
4. R.C.C roof provides superior protection, but heavy in earthquake. Need for
adequately braced vertical structure.
For well-fixed roof covering, strong connections between roof and vertical
structure are essential. Metal straps, bolts with washers on both ends instead of
simple nails are recommended. C.I sheet are screwed at every corrugation. Tiles are
36
fastened individually with the use of J-hook bolts and threaded/ twisted roofing nails.
Regular maintenance should involve regular checks, especially around the ridge and
corners. Weakened members should be replaced. C.I sheets should be tied strongly
to structural frames to resist uplift by strong winds. To further increase windresistance, number of purlins should be increased near eaves, ridge and corners.
Every sheet is to be fixed to purlins with hook bolts or twisted nails at each
corrugation.
More frequent fixings at edges can prevent uplift.
Adequate
connections should be made with nylon rope or good quality galvanized wires
(instead of jute rope). Roofing elements should be connected properly: purlin to
rafter, rafter to wall plate, wall plate to posts. Even though more expensive than
lean-to (akchala) and gable (dochala) roofing, hipped roofing (chouchala) is more
resistant to wind and protects gable end walls from exposure to rain and water
penetration.
Figure 2.22: The construction of rain water gutter.
Rain water gutters prevent creation of furrows around plinth by rain falling
down from roof eaves. They also prevent rainwater splashing on walls. Arsenic-free
rainwater can be collected for household use by keeping a container where the water
drains down. 100mm diameter PVC (polyvinyl chloride, i.e. plastic) pipe can be cut
into half lengthwise using a saw.
37
2.6
Significant Common Features of Traditional Houses in Bangladesh.
2.6.1
Arrangement of Traditional House in Bangladesh
The common arrangement of rural traditional house are having units that are
built together and sharing introverted courtyards. The main entry is from the south
or north side. Most of the units are orientated facing north-south. Toilets and
kitchens are separately built from the main living unit.
Master Bed
Figure 2.23: Arrangement of traditional house.
2.6.2 Upper Space
Upper space is the most common feature of all types of the traditional houses
in Bangladesh, which plays a vital role in thermal environment of the living space.
The upper space has one exposed roof on top and at the bottom are wooden plank
floor. This upper space is also use as a store.
38
Figure 2.24: The ladder of upper space entry and window opening of the upper
space.
The upper space is also used as a store in all seasons. The upper space has a
wooden plank or bamboo or C.I sheet ceiling as the inside and on the outside C.I.
sheet with wooden frames. This accessible upper space has a secured wooden door
from the main bed area. Maintenance of the upper space is accessible by a wooden
ladder. Adequate number and size of windows are built, which are oriented along
the prevailing wind flow direction to allow cross ventilation of the upper space.
Upper space also protects the indoor space from the direct solar radiation and heat.
In flood seasons all household things are kept in the upper space. Occasionally,
during summer night people also stay in the upper spaces.
39
Upper space in different types of traditional houses in Bangladesh are shown
in figures 2.25, 2.26 and 2.27
C.I. sheet
Upper
window
Wooden
plank
ceiling
Figure 2.25: Upper space in a stilts house during construction.
C.I. sheet
Upper
window
Wooden
plank
ceiling
Figure 2.26: Upper space in a wooden house.
C.I. sheet
Bamboo
mats with
bamboo
frame
work
ceiling
Figure 2.27: Upper space in a bamboo house.
40
The upper space wall opening is exposed to allow better airflow and
ventilation. Extended roofs protect the wall openings of the upper space from sun
and rain.
6'-13
4"
corrugated sheet
wind flow
3'-6"
30°
1'-73
4"
high window
ceiling ( wooden plank)
9'-6"
17'-33
4"
3'
semi-public space
private area
11'
9'-6"
entry from south gets importance
window
wooden plank floor
1'-6"
1'
wooden post
SECTION OF TRADITIONAL HOUSE
Figure 2.28: Upper space wall opening in Stilts house.
Upper ventilation
Figure 2.29: Upper space ventilation of Bamboo house and Mud house.
41
2.6.3
Traditional Houses are Rebuiltable Structure
The houses in Bangladesh are generally rebuiltable structure and easy to
repair after floods. Detachable lower panels made of cheap, perishable materials
such as straw, reeds and rushes or jutesticks are replaced after wet seasons without
affecting the upper walls. Painting with bitumen for damp proofing can be done on
bamboo mat walls and C.I. sheet walls. Easy to rebuilt and replace from one place to
another place according to the owners demand.
Figure 2.30: Easy repairing of the traditional house.
2.6.4 Window of Traditional House
Adequate number of 12 and size of windows (1.2m by 1m) are oriented along
the prevailing wind flow direction to allow cross ventilation of indoor and upper
space in the traditional house.
42
Figure 2.31: Windows of the traditional house in Bangladesh.
2.6.5
Elevated Floor
Floors are raised from ground level as protection from flood in the monsoon
period.
This elevated floor height of the house is different in different areas
according to the level of flood water.
Figure 2.32: Elevated floor of the traditional house in Bangladesh.
43
2.7
Upper Space Design from the User Demand
Bangladesh is an agricultural country. Culturally, people need to store their
reserve corns on the upper space of all times. In the post monsoon periods, people
accumulated a huge amount of paddy, wheat, beans, etc at a time. So people need a
huge storage space and the upper space serves this purpose.
Figure 2.33: The entry of upper space and use of upper space as store.
30°
Upper
Upper
space
semi-public space
Entry of
Upper
private
elevated seconday deck used as bed
( local name " cabin ")
variable height
wooden post
Master Bed room section
Figure 2.34: The entry way to upper space of the traditional house in section.
The monsoon is the longest season covering the months of June to September,
a period with heavy rains (781mm to 1499 mm recorded in Dhaka), with the average
relative humidity above 80% and an average temperature of 31ºC
44
Figure 2.35: The flood condition of 2005 in Dhaka city and suburban area.
During this period, for heavy rainfalls and melting of Himalayan’s ice, flood
occurs in Bangladesh for two or three months of every year. During flood periods,
floors of the house and the surrounding are flooded which force people to take their
necessary household items to the upper spaces.
2.8
The Reason of Selection of the Stilts House for this Research
By general comparison between rural and urban houses, it is evident that
rural houses are extensively protected from effects of solar radiation by trees, which
produces its own microclimate.
Traditional built forms of the rural area often
includes sound solution for climatic problems. The temperature difference between
rural and urban areas is 4ºC to 5ºC (Mallick, 1993). In urban areas, the construction
activities associated with urbanization appear to increase the radiation of heat. It is
45
selected for this reason which strongly justifies the study of the thermal performance
of the traditional house in its worst condition in a very dense Dhaka city.
According to climatic zone, Dhaka is situated in the south-central zone.
Economical status and living standard of people of Dhaka is comparatively higher
than others zone of Bangladesh. The construction cost of stilts houses is more than
all other types of traditional house.
Table 2.2, shows the materials used for traditional houses. The percentages
between materials of roof are, straw/ bamboo 13%, tiles/C.I. sheet 60% and
cement/flat roof 27%. Therefore, the percentage of stilts house is higher then other
types of traditional house in Dhaka.
Table 2.2:
State of houses by materials of walls and roofs in Dhaka city.
STATE OF DWELLINGS UNITS (HOUSES) BY MATERIALS OF WALL AND ROOF
IN DHAKA CITY
MATERIAL OF WALL
Straw, bamboo
Mud,un-burnt brick
C.I. Sheet, metal
Wood
Cement/brick
Total
TOTAL NO OF
HOUSEHOLD
MATERIAL OF
ROOF,STRAW,BAMBOO
TILE/C.I.
SHEET
342,820
125,467
142,319
2,969
474,803
111,690
21,871
3,773
248
1,704
231,130
103,596
138,546
2,721
176,462
296,637
1088378
139286
652455
296637
Source: Bangladesh Population Census 1991.vol 3. Urban Area Report, 1997
This is the reason to select the stilts house in this research.
CEMENT
46
Some pictures of the physical conditions of traditional houses at different
areas in Dhaka city are shown below in figure 2.36.
Pallabi
Uttara
Gulshan
Badda
Tejgaon
Khilgaon
Figure 2.36: The physical conditions of traditional house at different areas in
Dhaka city.
47
2.9
Conclusion
Traditional houses of Bangladesh reflect a deep understanding of social,
cultural impact of people and response to local environment and climate. Every year,
the traditional houses play a vital role during natural disasters like floods, cyclones
etc. The traditional houses in Bangladesh are well suited to its climate by the
practical use of building materials which subsequently help to increase as effective
comfortable living environment. There is no doubt that the young generation can
learn from this solution that has been adopted in the traditional house in terms of a
good sustainable architectural concept.
CHAPTER 3
CLIMATE OF BANGLADESH
3.1
Introduction
The elements and components constituting the landscape of cities affect the
regional climate, through a complex interaction generating distinct microclimates.
Although there are numerous processes occurring in an urban climate system, each
having their own mechanistic interpretations such as, radiative exchanges,
evaporative processes, they are essentially derivations from the regional climate.
Appreciation of the environmental characteristics at a regional scale can contribute
towards a proper evaluation at an urban scale.
The following section analyses, the climate problem and potentials regarding
the tropical city of Dhaka, Bangladesh where references are made to human comfort
issues. An understanding of its environmental characteristic and their energetic,
implications are particularly important to the later sections of this work where the
result of field investigations is discussed. More importantly, this chapter will help in
identifying local environmental particulars and those having strong local deviation.
49
3.2
Climate of Bangladesh: Classification and Outline
In terms of ecological region or biomes¹ described by UNESCO (Lean 1990)
Bangladesh, lying between 20º34′ N to 26º33′ N and 88º 01′E to 92º 41′E, is in the
Indo-Malayan Realm.
The characteristics of biomes result from a complex
interaction of climate, geology, water resources and latitude. Application of such a
classification based on ecological regions, is limited in terms of identifying
environmental factors related to human comfort. Similarly, a number of
classifications have been applied to appraise Bangladesh’s climate (Rashid, 1991).
These classifications generally focus on agro-climate issues, such as the one by
Thorn Waite, based on temperature and precipitation and Koeppen’s Classification,
based on temperature and precipitation (Houghton, 1985). Although some of the
aspects of these classifications are relevant to urban climatology, it is important to
identify the climatic variations with regard to a specific climate problem in human
comfort. Classifications, such as Terjung and Maunder’s Human Climatic Index,
based on 13 climate features (Houghton, 1985) or a simpler classification by
Figure 3.1:
Location of Bangladesh in the World Map
1 Biomes describe the ecological characteristic of an area if people had not altered the natural environment
50
Atkinson, based on air temperature and relative humidity (Koenigsberger, 1973),
address the issue of comfort in the context of a regional climate.
Figure 3.2:
Regional map showing radar coverage (solid bold line, left panel).
Rain-gauge location (plus mark, right panel) throughout Bangladesh with the station
names.
The climate of Bangladesh, based on the widely used classification by
Atkinson (Koenigsberger, 1973), is categorized as warm-humid.
Generally the
climate has short and dry winters while the summer is long and wet. Although a
large part of the country’s land mass lie above the Tropic of Cancer, the nature of the
climate being tropical is attributed to the regional geographical character.
The
Himalayan mountain range and Tibet Plateau being in the north causes a significant
amount of rainfall (Hossain and Nooruddin, 1993; Rashid, 1991). The humidity is
fairly high throughout the year and especially during the months June to September
when it is often over 80%.
Meteorologically the climate of Bangladesh is categorized into four distinct
seasons -- winter, pre-monsoon, monsoon and post-monsoon (Hossain & Nooruddin,
1993), where the winter is cool and dry, the pre-monsoon is hot and dry, monsoon
and the post-monsoon periods are hot and wet. The winter months, December to
51
February, are characterized by infrequent rains, cold northerly winds, mean
temperature 21°C and maximum below 26°C. In the northern part of the country, the
minimum temperature in winter often drops below 10°C. The pre-monsoon period
covers the months March, April and May and is characterized by occasional
thunderstorms, and a maximum temperature of 34°C. The monsoon is the longest
season covering the months June to September, a period with torrential rains 781mm
to 1499 mm recorded in Dhaka, with the average relative humidity above 80% and
an average temperature of 31 °C. The post-monsoon season ranges between the
months October and November. It is also regarded as a transitional period (winter)
with infrequent rains and temperatures below 30°C.
As regards to local traditions, six seasons are identified, namely - Grishha
(Summer), Barsha (Rain), Sharot (Autumn), Hemanta (late Autumn), Sheeth (Winter)
and Bashanta (Spring). There are many festivals and celebrations associated with
the different seasons. They are often based more on the visual appreciation of
changing atmospheric conditions as well as of changing of flora and fauna. The
variety of seasons has always been, and continues to be, a source of inspiration for
art and culture of the country. Interestingly the months of the Bangla Calendar,
instead of the seasons, have been traditionally considered to be a more appropriate
reference in the context of indigenous agricultural practices. Thus in many ancient
proverbs pastoral references have often been found to be made with regard to the
Bangla months instead of the seasons (Khatun, 1993; Pande, 1990). Similarly
proverbs relating to architecture refer to the Bangla months. Although there are 12
months in a Bangla year, the months very loosely approximate with that of the
Gregorian calendar hence any exact correlation is imperfect (Table3.1). It is
interesting to note that as far as local traditions are concerned, a wide range of
variation have been identified in a climate characterized with moderate changes in
the environmental parameters. This is particularly evident when comparisons are
made with the variations observed in the other regions of the Tropics.
Identification of each of the seasonal divisions may hold true in terms of their
holistic properties and actually attempts have been made to equal these in
meteorological terms (Rashid, 1993). However some of the divisions are too subtle
or insignificant in terms of environmental change. As far as climatic effects are
52
concerned, in the urban areas the environmental cues (i.e. aromatic traits of flowers
and plants, flora & fauna) reflecting the subtle rhythms are largely absent, hence
traditional seasonal categorizations are redundant in cities which have a climatic
system of their own. However it would be an interesting proposition to reconstitute
these subtle seasonal variations in urban leisure spaces by sensitive landscaping.
Table 3.1:
Classification of the seasons and weather condition of Bangladesh.
Bangla
Calendar
Month
Traditional
Seasons
Meteorological Seasons
Gregorian
Calendar
Months
Chaitra
Baishakh
Jaishtha
Ashaar
Srabon
Bhadra
Ashin
Kartik
Arahayon
Poush
Magh
Bashanta
Grisha
Grisha
Barsha
Barsha
Sharat
Sharat
Hemanta
Hemanta
Sheet
Sheet
Pre-monsoon (hot-dry)
Pre-monsoon (hot-dry)
Pre-monsoon (hot-dry)
Monsoon (hot-wet)
Monsoon (hot-wet)
Monsoon (hot-wet)
Monsoon (hot-wet)
Post monsoon (hot-wet)
Post monsoon (hot-wet)
Winter ( cool-dry)
Winter ( cool-dry)
March
April
May
June
July
August
September
October
November
December
January
Ave.
air
Temp
For
91-00
(ºC)
26.6
28.9
29.0
29.5
29.1
29.2
29.0
28.0
24.5
20.3
18.8
Falgun
Bashanta
Winter ( cool-dry)
February
21.9
63.6
70.9
78.4
82.3
84.0
83.6
83.5
80.7
75.7
74.4
72.4
Mean
Rainfal
l
For
91-00
(mm)
69
120
342
267
371
335
293
197
26
13
11
Mean Wind
Speed
& Direction
For
91-00
(m/s )
2.4 (SW)
2.9(SW)
2.4 (S)
2.3 (SE)
2.2(SE)
2.2(SE)
2.1(SE)
2.1(N)
1.3(NW)
1.6(NW)
1.4(NW)
67.0
27
1.9(N)
Mean RH
For
91-00
(%)
Source climate division, Bangladesh Meteorological Department, Agargaon, Dhaka,
2006
3.3
Climatic Regions of Bangladesh
There are perceptible variations of the climate in different parts of the
country. These variations are identified with seven sub zones across the country
(Rashid, 1993). These are South-Eastern Zone, North-Eastern Zone, Northern Part
of Northern region, North-Western Zone, Western Zone and South Central Zone
(Figure 3.3). One of the most important factors contributing to this variation is the
nature of topography (of the region and its surroundings). For example, the main
cause of intense rainfall in the northern part of the Bangladesh is the presence of the
Meghalaya Plateau, while in the South-Eastern part the Bay of Bengal is a major
source of the rain and storm. The characteristics of the climatic sub zones are
outlined below (after Rashid, 1993; Masud Hassan Chowdhury, 2005).
53
Figure 3.3:
The climatic sub zones of Bangladesh
54
3.3.1
South-eastern zone (A)
It comprises the Chittagong sub-region and a strip of land extending from
southwest Sundarbans to the south of Comilla. The hills over 300m in height have
north-eastern zone climate. The rest of the area has a small range of temperature,
rarely goes over a mean of 32°C and below a mean of 13°C. Rainfall is heavy,
usually over 2,540 mm. In winter dewfall is heavy.
3.3.2
North-eastern zone (B)
This zone includes most of east and south Sylhet and a wedge shaped strip
south of the Meghalaya Plateau. Here too, mean maximum temperature is rarely
above 32°C but mean minimum is 10°C and below. Average humidity is even more
than in south-eastern zone. In this zone winter rain is appreciable. In monsoon
season rainfall is 3,200 mm. Fog is very common in winter.
3.3.3
Northern part of the northern region (C)
This is an area of extremes. In summer the mean maximum temperature is
well above 32°C whereas in winter the mean minimum is below 10°C. The summer
is dry, with a scorching westerly wind, but the rainy season is very wet, with 2,000
to 3,000 mm of rainfall.
3.3.4
North-western (D)
Except that the extremes are less and the rainfall is lower, this zone is similar
to northern part of the northern region.
3.3.5
Western zone (E)
It comprises greater Rajshahi district and parts of adjacent districts. This is
the driest area in Bangladesh with rainfall generally below 1,500 mm and summer
humidity less than 50%. Mean summer maximum temperature is over 35°C.
55
3.3.6
South-western zone (F)
Here the extremes of the zones to the north are somewhat tempered. Rainfall
is between 1,500 mm and 1,800 mm. Mean summer maximum temperature is below
35°C.
3.3.7
South-central zone (G)
In this zone rainfall is abundant, being above 1,900 mm. The range of
temperature is, as can be expected, much less than to the west, but somewhat more
than in South-eastern zone. This is a transitory zone between the South-eastern,
North-western and South-western zones.
Most of the severe hailstorms, and
tornadoes are recorded in this area. The monthly mean maximum temperature is
35.4ºC in summer and the monthly mean minimum temperature is 11ºC in winter.
Dhaka city along with other town such as Mymensingha and Tangail are included in
this region.
3.4
Urban Climatic Elements of Dhaka City
The city of Dhaka lies between longitudes 90°20' E and 90°30' E and
between latitudes 23°40' and 23°55'N, with three sides bounded by the river
Buriganga in the south, the Tongi Klual (canal) in the north and the Turag River in
the west. The present city covers an area of 256 km² and the present structure plan
for the city covers all area of 280 km². Several investigations have been conducted
to assess Dhaka's urban climate characteristics (Asaduzzaman, 1992; Habib el al,
1993; Hossain, 1993; Ahmed et al, 1993; Huq, 1993).
Due to the physical development and location, the climate characteristics of
one city differs from other and further modified in different locations within the city
depending on difference in surface qualities, density, heights (three dimensional
objects) and other related factors (Koenigsberger et al, 1973); as a result climate
characteristics of Dhaka city differ from other cities of Bangladesh. This fact is
56
more pronounced in developed nation where physical features of urban areas have
more difference with surroundings, than tropical environments of developing
countries (Jauregui, 1993). However, several investigations have been conducted to
assess Dhaka's urban climate characteristics (Asaduzzaman, 1992; Hossain and
Nooruddin, 1993; Ahmed, 1993). The following review of urban climatic factor is
based on those investigations and on data from meteorological sources of the Dhaka
city.
3.5
Temperature
The temperature profile of Dhaka city based on metrological data shows a
clear congruity, with the regional pattern and according to data accounts for 1950 to
1980 exhibits monthly maximum average temperatures recorded in March, April and
May (pre-monsoon period) are relatively higher; reaching the highest at 34.5°C in
April. During June to September (monsoon period) mean maximum temperature
swings between 25ºC to 26°C and average temperature remains steady at 28.6 ºC. In
winter the temperature drops to an average of 18.6º C while mean minimum is
11.7ºC recorded in January.
Table 3.2:
Air temperature profile of Dhaka city year 1950-1980
Air Temperature Profile of Dhaka City for 1950-1980
Mar April May
Pre-Monsoon
Jun
Jul Aug
Monsoon
Sep
Oct Nov
Post-Mon.
Dec
Jan Feb Ann
Winter
Mean Max
32.6 34.5 33.0 31.4 31.0 31.1 31.4 30.8 28.7 26.0 25.5 28.5 30.4
Temp. ºC
Mean Min
19.7 23.5 24.8 25.8 26.2 26.1 25.9 23.7 18.2 13.3 11.7 14.5 21.1
Temp. ºC
Ave. temp.
26.2 29.0 28.9 28.6 28.6 28.6 28.6 27.3 23.5 19.7 18.6 21.5 25.8
ºC
Source climate division, Bangladesh Meteorological Department, Agargaon, Dhaka,
2006
The temperature profile of the next decade (1981-1990) shows a slight fall of
highest monthly mean maximum temperature by 1ºC in April.
Fluctuation of
average temperature in monsoon period is observed. Mean minimum and average
57
temperature in January has increased by 1.5ºC and 0.9º C respectively. Again
increase of annual temperature in all three categories should be taken into account.
Air temperature profile of Dhaka city year 1981-1990
Table 3.3:
Air Temperature Profile of Dhaka City for 1981-1990
Mar April May Jun
Pre-Monsoon
Jul Aug Sep Oct Nov Dec Jan Feb Ann
Monsoon
Post-Mon.
Winter
Mean Max 32.4 33.4 33.1 32.4 31.5 31.9 31.9 31.8 29.9 26.7 25.8 28.4 30.8
Temp. ºC
Mean Min 20.5 23.5 24.6 26.3 26.3 26.5 26.0 24.0 19.3 14.7 13.2 15.8 21.7
Temp. ºC
Ave.temp. 26.5 28.5 28.9 29.3 28.9 29.2 28.9 27.9 24.6 20.7 19.5 22.1 26.5
ºC
Source climate division, Bangladesh Meteorological Department, Agargaon, Dhaka,
2006
Table 3.4:
Air temperature profile of Dhaka city year 1991-2000
Air Temperature Profile of Dhaka City for 1991-2000
Mar April May Jun
Pre-Monsoon
Mean Max
Temp. ºC
Mean Min
Temp. ºC
Ave.temp.
ºC
Jul Aug Sep Oct Nov Dec Jan Feb Ann
Monsoon
Post-Mon.
Winter
32.6 34.0 33.2 32.7 31.8 31.9 32.1 32.0 29.8 26.6 25.0 28.0 30.8
20.6 23.7 24.7 26.3 26.4 26.5 25.9 23.9 19.2 14.0 12.7 15.9 21.7
26.6 28.9 29.0 29.5 29.1 29.2 29.0 28.0 24.5 20.3 18.8 21.9 26.2
Source climate division, Bangladesh Meteorological Department, Agargaon, Dhaka,
2006
Table 3.5:
Air temperature profile of Dhaka city year 2002-2006.
Air Temperature Profile of Dhaka City for 2002-2006
Mar April May Jun Jul Aug Sep Oct Nov Dec Jan Feb Ann
Pre-Monsoon
Monsoon
Post-Mon.
Winter
Mean Max Temp. ºC 27.5 29.0 30.5 29.8 29.4 29.5 29.0 28.0 24.3 21.0 19.8 24.9 26.9
Mean Min Temp. ºC
Ave.Temp.
ºC
24.5 27.6 27.9 28.4 28.6 28.7 27.7 26.9 23.5 20.3 16.3 21.9 25.2
26.5 28.4 29.1 28.8 28.9 29.1 28.5 27.4 24.0 20.8 18.5 23.0 26.1
Source climate division, Bangladesh Meteorological Department, Agargaon, Dhaka,
2006
The data for the year 2002-2006 indicates some changes in magnitude of data
from the previous sets of data 1950 -2000. Pre-monsoon period accounts for higher
58
maximum temperature 30.5 ºC in May. In previous decade the highest temperature
recorded in April 34.5 ºC.
The data for the year 1991-2000 indicates some changes in magnitude of data
from the previous sets of data 1950 -1990. Pre-monsoon period accounts for higher
maximum average temperature, while in April it is highest 34.5 ºC and the overall
temperature profile of April has increased by 0.4 ºC as compared to temperature
profile of the previous decade. Mean maximum temperature in monsoon period
indicates relatively higher temperature over 31 ºC as compared to previous one. In
cold season, especially in January the average temperature is recorded as 18.8 ºC and
the mean minimum is 12.7º C for the same month. Annual temperature profiles for
both decades are of same magnitude (Table 3.4).
Figure 3.4:
Monthly Mean Min and Max temperature from 1950 to 2006.
Figure 3.4 shows the monthly mean maximum and minimum temperature
profile for four-time span.
Over heated temperature is a growing environmental concern for Dhaka. The
problem is best illustrated by the probabilistic estimates based on data collected over
a number of years. Probabilistic extreme estimates for Dhaka predicts monthly
highest maximum temperatures in April as high as 39.1ºC, 40.2ºC, 41.0ºC (in year
59
out of 4 years, 10 years and 25 years respectively), while the lowest minimum
temperature in January are 7.4ºC, 6.4º C, 5.6 °C (in 1 year out of 4 years, 10 years,
25 years respectively) (Karmakar and Khatun, 1993) (see detail in Chapter four).
Recent meteorological observations in the pre-monsoon period a temperature of
36.5º C (1995) indicating a possible trend towards increased overheating due to
Dhaka's inexorable urban growth.
3.6
Relative Humidity
Relative humilities being a function of prevailing temperature are found to be
inversely related to the urban heat island intensity. Higher temperatures yield lower
relative humidity level (all other conditions remaining the same). Humidity also
varies depending on the density of the surrounding built form e.g. in Motijeel area, a
major commercial district, a pocket of low humidity was observed in January where
the heat island² effect was maximum (Ahmed, 1995). The inverse relationship
between relative humidity and temperature exists in heat island and warm pockets
located away from water bodies. Warm pockets adjacent to Burigonga river have
found high relative humidity. Investigation done by Hossain and Nooruddin (1993)
indicates 2-4% in annual average humilities between Dhaka and adjacent rural areas.
Another study indicates that with 50 % impervious cover, run off increases 200%
compared with rural conditions concludes that urban humidity near the surface
decreases due to the rapid run-off (Ahmed, 1994).
Urban, suburban and rural relative humidity exhibits a marked diurnal
variation and generally decreases towards city center. During the afternoon in the dry
seasons difference may be as high as 12 % and nocturnal difference can be high as
13 % in the same season (Oguntoyinbo, 1984).
²Heat island phenomena are the result of urban/rural energy balance and stability differences which in turn produce different
rates of near surface cooling and warming (Oke T.R., 1982;). The air in the urban canopy is usually warmer than that in the
surrounding countryside. This urban heat island effect is probably both the clearest and the best-documented example of
inadvertent climate modification. The exact size and form of this phenomenon varies in time and space as a result of
meteorological, location and characteristics.
60
According to data provided by the metrological office of Dhaka, it has been
found that the mean annual relative humidity between years 1950 to 1980 is 76%.
Relative humidity is highest in monsoon season 86.4% and comparatively low in
winter season, while lowest being in March 61 %. However, data for the next
decade indicates rise of annual relative humidity by 6 %, while during monsoon it
decreases by almost 2% Mean relative humidity is lowest for the month of February.
Table 3.6:
Monthly and annual mean relative humidity of Dhaka city for 1950 –
2006
Monthly and Annual Mean Relative Humidity of Dhaka City for
1950-1980, 1981-1990 and 1991-2000
Mar Apr May Jun Jul Aug Sep Oct Nov Dec Jan Feb Ann
Pre-Monsoon
Monsoon
Post-Mon.
Winter
Mean RH for
61.0 70.0 79.0 86.0 86.0 86.0 85.0 81.0 75.0 71.0 69.0 63.0 76.0
50-80
(%)
Mean RH for
81-90
65.0 73.8 78.7 84.0 86.4 84.3 84.6 78.6 73.1 73.8 71.7 64.3 76.6
(%)
Mean RH for
63.6 70.9 78.4 82.3 84.0 83.6 83.5 80.7 75.7 74.4 72.4 67.0 76.5
91-00
(%)
Mean RH for
02-06
60.6 69.4 72.4 81.0 81.0 79.2 81.2 76.8 69.6 69.0 72.2 70.4 61.4
(%)
Source climate division, Bangladesh Meteorological Department, Agargaon, Dhaka,
2006
From other set of data for the period between 1991 to 2000 the same source
shows annual drop from the previous decade by 0.1 %. The highest and lowest
monthly mean values are 84% and 63.6.0% designated to July and March
respectively. Interestingly except the middle period in other instances the lowest
value of relative humidity is observed in March, which is in pre-monsoon season
(Table 3.6). The humidity profile of all these four time-span illustrates the magnitude
in almost same nature.
61
Figure 3.5:
3.7
Monthly Relative Humidity from 1950 to 2006.
Rainfall
After a relatively dry winter, Dhaka remains under the grip of monsoon from
June to September, a period that brings torrential rains. More than 75% of annual
rainfall occurs in this period (Hossain and Nooruddin, 1993).
62
Table 3.7:
Monthly and annual mean rainfall of Dhaka city for 1950–2000
Monthly and Annual Mean Rainfall of Dhaka City for
1950-1980, 1981-1990 and 1991-2000
Mar Apr May Jun Jul Aug Sep Oct Nov Dec Jan Feb Ann
Pre-Monsoon
Monsoon
Post-Mon.
Winter
Mean Rainfall for 50-80 69 120 258 397 386 326 264 158 26
(mm)
Mean Rainfall for
81 199 302 357 377 269 348 159 52
81-90
(mm)
Mean Rainfall for
69 120 342 267 371 335 293 197 26
91-00
(mm)
8
12 20 2044
12
6
13
11 27 2093
23 2206
Source climate division, Bangladesh Meteorological Department, Agargaon, Dhaka,
2006
The total annual average rainfall for above three-time span exceeds 2000mm,
where highest rainfall 2206 mm occurred between 1981-l990 (Table 3.7). According
to the average total rainfall data (1950 - 1980), rainfall varies between 397 mm to
264mm during the month of June and September respectively, while the is record in
December (8 mm). The next set of data for the time span between 1991-1990
indicates the same pattern of rainfall with highest intensity in monsoon period with
highest monthly average in July 377 mm and lowest in January (6 mm). In both
cases one month shifting is observed. From more current data compiled between
1991-2000 it has been observed some fluctuation in rainfall between May and
September (Figure 3.6). The magnitude of highest monthly average rainfall has
changed but the time has not altered, where the maximum precipitation level in
Dhaka city is in the month of July 371mm and minimum in January (11 mm). So in
three instance monsoon accounts for heavy rainfall which is far above than other
seasons and clearly evident in figure 3.6. Some of the extreme values can be
presented here, the ever highest rainfall of 24 hours occurred on 14th July 1956
where the magnitude was 326 mm, while the heaviest rainfall of one hour was 85
mm recorded in 3rd March.1961.
Higher rainfall is comparison with the rural surroundings have been reported
in Dhaka. This has been attributed to phenomenon often observed in large urban
areas. In such circumstances the air rises (due to increased buoyancy of the heated
urban area) to the upper layer of the atmosphere, where the parcel of air cools until it
63
can no longer hold moister and precipitation (Hossain and Noruddin, 1993;
Padamanbhamurty and Bahl 1984; Geiger, 1961).
Figure 3.6:
The Rainfall Profile of Dhaka City.
Rainfall is one of the most important causes of internal flooding in Dhaka
city and requires serious attention. This is due to the fact that large impermeable
surface of the city create substance runoff while the existing drainage systems are
incapable to cope with such magnitude of rainfall.
3.8
Wind Speed and Direction
The increases in surface roughness within cities cause reduction of wind
speeds mainly during the day (Jauregui 1984). The variation in wind speed between
meteorological station and site will depend largely on ground cover and topography.
The wind speed is usually measured in flat open location (eg. airport) at a height of
10 meter above ground level. To convert this to an equivalent wind speed at 3 meter
in flat urban or sub urban locations, the wind speed must be multiplied by a
reduction factor as shown in Table 3.8. This table illustrates the average reduction
64
factor within dwellings with open windows facing the wind. These reduction factors
will only give an approximate indication of the likely variation and will not be
applicable in heavily built-up areas, close to high-rise buildings or major obstruction.
Table 3.8:
Height
10 m
3m
Average reduction factors for wind in different location.
Location
Open, flat
unobstructed
Terrain
Suburban or
Wooded
1.00
0.40
0.15
0.70
0.30
0.10
0.5
0.2
0.07
0.3
0.12
0.04
In the open
In building with cross ventilation
In building with ventilation
In the open
In building with cross ventilation
In building with ventilation
Urban
0.3
0.12
0.04
0.15
0.06
0.02
Source climate division, Bangladesh Meteorological Department, Agargaon, Dhaka,
2006
In Dhaka where humidity ranges between 80 % and 86% during hot-wet
period, air flow plays an important role in thermal comfort. The meteorological data
(1950-1980) based on condition measured in open location (Table 3.9) shows that
prevailing wind speed in Dhaka is comparatively high in monsoon period starting
from June to September where the value is over 3 m/s and the highest being in July
4.2 m/s. The prevailing wind direction is southeasterly during this season while the
lowest speed is recorded in November and January l.4 m/s and wind direction is
predominantly northwesterly for both months.
Table 3.9:
Monthly mean prevailing wind speed and direction of Dhaka city
Monthly Mean Prevailing Wind Speed and direction of Dhaka City for
1950-1980, 1981-1990 and 2002-2006
Mar Apr May Jun Jul Aug Sep Oct Nov Dec Jan Feb
Pre-Monsoon
Monsoon
Post-Mon.
Winter
Mean Wind Speed for 50-80
(m/s)
2.8 2.8 3.9 3.3 4.2 3.9 3.1 1.7 1.4
1.9 1.4 1.7
Mean Wind Speed for 81-90
(m/s)
2.4 2.9 2.4 2.3 2.2 2.2 2.1 2.1 1.3
1.6 1.4 1.9
Mean Wind Speed for 02-06
(m/s)
4.5 4.7 4.4 3.4 3.5 3.8 4.7 3.3 2.4
2.9 3.3 3.5
Prevailing wind Direction
SW SW
S
SE SE SE SE
N
NW NW NW
N
Source climate division, Bangladesh Meteorological Department, Agargaon, Dhaka,
2006
65
The prevailing wind direction in this period is southwesterly and south. Data
for the next decade illustrate significantly low magnitude of wind speed (Table 3.9).
From March to October there is no significant variation in wind speed 2.1-2.9 m/s.
Highest wind speed occurred in April 2.9 m/s while lowest in November 1.3 m/s.
Prevailing wind direction is same as for last thirty years.
As mentioned earlier that wind speed measurement varies considerable from
place to place depending on orientation, three dimensional characteristic and
vegetation and on level of measurement. Wind speed measurement in adjacent rural
area has been found to be higher than Dhaka. Moreover wind speed and direction in
open countryside is predictable, but in urban context these effects are almost totally
unpredictable because numerous obstructions are constantly modifying the
prevailing wind direction and speed. The average wind speed is much lower in cities
figure 3.7, testify this facts where the later data illustrates much lower average wind
speed than data collected from 1950-1980. Rapid urbanization after 1980 plays a
vital role in reduction of wind speed in Dhaka.
Figure 3.7:
The Wind speed Profile of Dhaka City.
66
3.9
Solar Radiation
The microclimate or site climate is characterized by the amount of solar
radiation received by that site and surrounding. Therefore, it is the single most
deciding factor for assessing the climate effects of the site due to its influence on
temperature and density of air, hence air speed and direction and humidity as well.
The amount of solar radiation received by the site depends on the following factors
(Koenigsberger et al, 1973).
i.)
Angle of incidence
ii.)
Atmosphere depletion i.e.
iii.)
The absorption of radiation by ozone vapors
iv.)
Duration of sunshine i.e. the length of daylight period,
v.)
The material characteristics the surrounding and
vi.)
The site itself i.e. absorption, reflection etc. of the site and
surroundings.
Before the year 2000, the meteorological department did not collect radiation
data regularly and the raw data are not processing yet. However radiation data
recorded for five years at Joydevpur Agro met Pilot station and for seven years at
Bangladesh engineering and technology by mechanical engineering Department are
only source to evaluate urban affect on incoming radiation (Huk and Hassan, 1993).
Data recorded at Bangladesh University of Engineering and Technology is in
urban context while meteorological data were collected in rural context. Higher
diffused radiation usually observed in urban areas due to surrounding built from and
hard surface quality. Therefore BUET data represent higher magnitude of global
solar radiation. The comparison (Table 3.10) indicates that the difference between
two measured values varies, between 13 % to 12 %, which is in fact very high
(Mojumder, 2000). Another reason high solar radiation in BUET may be that the air
over the city being more polluted, results in a noticeable decreases in atmospheric
clarity, causing a higher proportion of defuse radiation.
67
Table 3.10:
Monthly global solar radiation between BUET and Meteorological
Department of Dhaka.
Comparison of Monthly Global Solar Radiation Between
BUET and Meteorological Department of Dhaka
Mar Apr May Jun Jul Aug Sep Oct Nov Dec Jan Feb
Pre-Monsoon
Monsoon
Post-Mon.
Winter
Global Solar Radiation at BUET 4.66 5.05 4.55 4.01 3.65 3.75 3.75 3.60 3.61 3.15 3.25 4.01
(kWh/m² day)
Global Solar Radiation at
Met.Office (kWh/m² day)
Difference %
3.41 3.53 3.04 2.79 2.61 2.56 2.48 2.69 2.49 2.30 2.51 2.61
15 18 20 18 16 19 20
14
18
15 13 21
Source climate division, Bangladesh Meteorological Department, Agargaon, Dhaka,
2006
Data provided by Ahmed (1994) indicates that horizontal surface receives
highest amount of solar radiation 5329 Wh/m² in April and this value is fairly above
than values of rest of the months. Intensity solar radiation is also affected by angle
of incidence (as mentioned earlier) and orientation; therefore it is reduced in vertical
surface in table 3.11. Table also shows that the direct radiations in the east and the
west are higher than the north and south, while the north receives the lowest
radiation, which is very negligible.
According to BUET data, in pre-monsoon period, particularly during the
month from March to May, solar radiation on a horizontal surface is higher as
compared to rest of the year and is maximum in April (5.O5 kWh/m² day). Higher
ambient temperature in these months indicates the causal link with such level of
insulation. The insulation level is fairly constant between July to November, while
the minimum is recorded in December (3.15 KWh/m² day) (table 3.10). Although
there is a wide variation in monthly average extraterrestrial radiation during
monsoon and post-monsoon period, cloudy atmospheric condition during these
seasons result is the reduction (Figure 3.8). The clearness index during the month on
June and July is considerably lower (0.35) compare to other months highest observed
in February (around 0.5) as the incoming solar radiation is absorbed and reflected by
the particles in the atmosphere and by clouds (Figure 3.8).
68
Table 3.11:
Monthly global solar radiation, Diffuse radiation and Direct radiation
of Dhaka city.
Hour
6
7
8
9
10
11
12
13
14
15
16
17
18
Total
Global
Radiation
(Wh/m²)
Horizontal
34
167
320
475
607
697
729
697
607
475
320
167
34
5329
Diffuse Radiation
(Wh/m²)
North
13
61
108
151
185
207
215
207
185
151
108
61
13
1665
South
13
61
108
151
185
207
215
207
185
151
108
61
13
1665
East
West
North
13
13
0
61
61
12
108
108
0
151
151
0
185
185
0
207
207
0
215
215
0
207
207
0
185
185
0
151
151
0
108
108
0
61
61
12
13
13
0
1665
1665
24
Direct Radiation
(Wh/m²)
South
0
0
16
49
82
105
113
105
82
49
16
0
0
617
East
West
0
0
251
0
277
0
266
0
208
0
115
0
0
0
0
115
0
208
0
266
0
277
0
251
0
0
1117
1117
Source climate division, Bangladesh Meteorological Department, Agargaon, Dhaka,
2006
Figure 3.8:
Monthly Mean solar radiation over Dhaka and clearness index.
Therefore the diffused component of the radiation is significantly large and it
is clear from the fact that in spite of a wide variation of sunshine hours, the total
radiation incident on a horizontal surface has a comparatively marginal variation
(Figure 3.9).
69
Figure 3.9:
Monthly Mean cloud cover Dhaka city.
Another aspect of high cloud cover during those months over the city is that
the long wave terrestrial radiation to the space is absorbed particularly because of
low and medium could formation. Moreover the prevalence of low cloud that are
most affective layer in obstructing terrestrial long wave radiation to the sky dome,
are fairly constants. The potentiality to act as a thermal sink by the night sky is
severely reduced by such cloud cover hence during this months these diurnal
difference in temperature are small.
70
3.10
Conclusion
Although overheating is a major environmental concern for Dhaka for most
of the period, the combination of the environmental factors in the ambience during
those periods dictates the nature of the problem, i.e. overheating with dry or humid
conditions. Based on the discussions presented in the preceding section on the urban
climatic factors of Dhaka and their relative magnitude of the environmental variable
at different time of the year, the nature of the overheated condition can be identified.
Compare the environmental variables at different time of the year, indicating their
potential impact on the bio-climate.
It is observed that, from March to May
conditions with high air temperature is associated with high solar radiation, while
from October, condition with high relative humidity is associated with high air
temperature. In case of the former, minimizing the impact of solar radiation can
potentially moderate the overheated condition and in case of the latter, means of
optimizing airflow can contribute towards the moderation.
In wet-tropics
excessively humid condition with high ambient temperature is often the most
persistent environmental condition.
The scope of this thesis in terms of issues raised in the environmental agenda
is limited, as this work focuses on the environmental factors (air temperature and Rh)
that are relevant to thermal comfort and particularly to indoor comfort. The primary
concern of this chapter was to develop an understanding of the urban climate of
Dhaka and the basis for other relevant environmental concerns.
CHAPTER 4
PREVIOUS STUDY ON CLIMATE OF DHAKA CITY
4.1
Historical Background of Dhaka City
Dhaka flourished as a center of commerce and administration in the Mughal
period (1608-1764). During this period an early trend in the influx of population set
in and continues to this date. Dhaka was a provincial capital of the then East
Pakistan in 1948. After independence from Pakistan in 1971, Dhaka became the
capital of Bangladesh, which is one of the most densely populated countries in the
world. In 1948 Dhaka comprised of an area of approximate 50 sq. km and a
population of approximately 250,000. By 1979 the population had grown to 3.5
million, considerably exceeding the capacity of the 1959 master plan. The area of
the city now has grown to approximately 300 sq. km, with an estimated population
of 7.4 million, thereby making it one of the top twenty most populated cities in the
world (Linden, 1993). In spatial terms, the growth of the city did not match such
unpredicted population growth, particularly alter the independence.
The trend
continues with projections of' 13 million by the year 2010 (Ahmed, 1995). Old
Dhaka is characterized by very dense contiguous buildings usually 36 story tall,
narrow streets, and very few open spaces or parks, while new Dhaka is characterized
by a congested downtown with high-rise buildings, 5-6 story tall residential
buildings, interspersed with newly constructed high-rise apartment buildings,
relatively wider roads and more open spaces and some pockets of low-lying areas
with perennial stagnant water.
72
4.2
The Impact of Urbanization on Microclimate of Dhaka
People are attracted to urban areas because they offer a host of,
socioeconomic and cultural opportunities. This is especially true in many tropical
and subtropical countries where urbanization is growing at an uncontrollable rate,
which, in turn, deteriorates atmospheric environment (Taesler, 1991). Growth of
cities introduces a profound modification of climate by human activities, which is
not to be found any place else (Barry and Chancy, 1982)
The process of urbanization involves the construction of bridges, roads,
underground drainage system, and factories, which radically transforms the radiative,
thermal, moisture and aerodynamic characteristics of the pre-existing landscape, and
thus creates climate of its own. As a result, more energy is received and retained,
greenhouse elements (carbon dioxide, dust and other pollutants) are increased, and
evaporative flux is lowered and sensible heat flux increased. Studies show that
many large cities have experienced significant changes in cloudiness, precipitation,
radiation, energy, balance, temperature, air quality and visibility (Fortak, 1980;
Cleugh and Oke, 1986; Oke, 1982; Nkemdirim, 1988). The extent of urban climate
change varies from city to city, and it depends on the site and size of a city, land use
pattern, structure and density of buildings, traffic, industry, and other activities
(Ahmed, 1993b)
The construction activities associated with roads, pavements and buildings
increase radiation of heat. The high concentration of population and the nature of
economic activities are generally higher levels of income also lead to high-energy
consumption per capita and per unit of area. As a result heat island effect develops
and in turn leads to higher use of energy to counter its effects (Asaduzzaman, 1993).
Heat island intensities for Dhaka have been found to be 2.5 ºK in January (winter),
while it is insignificant in July, 0.6 °K (summer) (Ahmed, 1995). Urban Heat Island
intensities are usually found to be highest early in the morning, when urban and rural
surfaces are adequately cooled by means of long wave radiation evaporation and
convection, hence temperature difference between urban and rural are most
pronounced. During summer, the sky dome over Dhaka and its surrounding remain
overcast with cloud; therefore in both cases the nocturnal cooling potential of the sky
73
sink is reduced. Furthermore high surface winds in the city during summer have
been identified as the major cause of Low Heat Island Intensity (Hossain and
Nooruddin, 1993). While in the dry winter sky remains fairly clear and the rural
areas cools down to a lower temperature as compared to urban area. Urban heat
island investigation in mid latitude cities (Landsberg. 1981; Oke, 1982) where urban
geometry has been found to obstruct nocturnal cooling were in climatic regions
marked by cloudless night skies. In such conditions the open rural areas cool down
rapidly by long wave radiation. The complicated urban surfaces with reduced sky
view cannot cool down at the same rate as adjacent rural area, hence leading to heat
islands.
Table: 4.1
Location
Temperature difference between Dhaka city and Tangail (rural area)
Mean Minimum
Temperature ( ºC )
Mean Maximum
Temperature ( ºC )
Mean Annual
Temperature (ºC)
Temperature Difference Temperature Difference Temperature Difference
Dhaka City
Tangail
( rural)
21.4
30.6
0.5
20.9
25.8
0.4
30.2
0.4
25.4
Source: Hossain, M.E., Nooruddin, Md, 1993
However, mean annual temperature, mean maximum and minimum
temperature indicates that Dhaka has an urban heat island effect as shown in table
4.1. The table reveals that the urban heat island affects the minimum temperature
more than the both mean annual and the mean maximum temperatures.
The
temperature difference between urban (Dhaka) and rural (Tangail) is recorded 0.4 ºC.
The significant of such extreme phenomenon is indicative of the growing problem of
over heating in the context of Dhaka’s inexorable urban growth, which poses a
challenge for the urban house design. For this reason in this research for the field
measurement the area was select in dense Dhaka city
74
4.3
Historical Studies on Climate
James Taylor, who worked as a surgeon and was assigned to prepare a report
on the physical statistical aspects of Dhaka published his findings in a book
(Taylor,1839) in which he gave information regarding mean monthly temperature of
Dhaka for the period 1826-1836. Another data on mean monthly temperature and
humidity of Dhaka city for the period 1958-1962 is available in Dhaka district
Gazetteer (District Gazetteer of East Pakistan, 1962) In Table 4.2 the average of
monthly average of five hot months, i.e. April to August as found in the historical
studies and recent studies have been presented.
Table: 4.2
Changes in mean monthly temperature and humidity of Dhaka City
CHANGES IN MEAN MONTHLY TEMPERATURE AND HUMIDITY OF
DHAKA CITY THROUGH 173 YEARS
Source
Period
APRIL
MAY
JUNE
JULY
AUGUST
Temp. Hum
Temp. Hum.
Temp. Hum
Temp. Hum.
Temp.Hum
30.8-_____
30.1-_____
30.1-______
29.7-_____
29.2-82.0
28.5-87.1
28.6-88
28.6-89.3
29.0- 79
28.7-86
28.6 – 86
28.6- 86
28.6-77
30.2 - 82
29.1 – 86
29.7-64
Talor (1827-1836)29.7-_____
average of 10 years
Dist. Gazetteer
29.8-72.3
Average of 5 years
Statistical Yearbook
Year 1992
29.0- 70
Statistical Yearbook
Year 1997
26.1-74
Source: Sharma, A study of the factors for thermal comfort in residential high rise in Dhaka
city. 2002
75
In order to show the changes more vividly, the above information has been
shown in (Figure 4.1)
Figure 4.1:
Temperature and humidity changes of Dhaka city
Since there was no mention of humidity in Taylor's account, the above
comparison of humidity presents a period of 42 years only. In the above Table 4.2
and Figure 4.1, there is no indication that there was any gradual increase or decrease
of temperature or humidity in Dhaka city through a period of 173 or 42 years. In
case of temperature, gradual decrease may be noticed in the months of April and
May, decrease in July and no change in June and August. In case of variation of
humidity through 52 years there are gradual decreases in May, June, July and August
and increase in April.
From a number of indications like (a) melting of ice at the arctic regions, (b)
ever increasing of deposit of C02 in the upper boundary layer etc, the conclusion was
mentioned that global temperature is increasing. It has also been assumed that the
76
deposit of C02 in the upper boundary layer shall nearly double by the year 2030
(Assaduzzaman, 1993).
The materials used in buildings, roads, pavements etc.
absorb heat. Buildings and structures retard air movement creating stagnancy and
causing growth of 'heat island'. By those considerations the table 4.2 should have
indicated some increase in the temperature of Dhaka city through this period, but it
did not increase because of a possibility that the process or system in which the
measurements data shown in table 4.2 were taken might not be inaccurate. It may be
mentioned that the readings were taken at different locations of the Dhaka city.
Initially it was at the old weather station situated at old Dhaka, and then it was
shifted to Kurmitola airport and was later undertaken by the civil aviation
department.
A new weather station was established at Agargaon.
Later, the
meteorological department began to continue supplying climatic data, even though
the measurements were taken from different locations. This might logically lead one
to believe, even though the above data have been collected from authentic sources,
they do not reflect the real picture. Nevertheless the data is interesting as it shows
that the general populace in this city has been experiencing and becoming habituated
to very steady average conditions over large period of time.
4.4
Previous Studies on Micro-Climates in Dhaka City
In the built-up areas with closely spaced tall buildings, there remains every
possibility that there would be stagnant air trapped in narrow gaps in between builtmasses. The air flowing through the open country might skip the built structures.
Cool air cannot enter in these areas and in addition heat trapped in narrow gaps
cannot escape. Water bodies, green trees, grasses etc. reduce heat by the process of
evaporation of water. In congested cities, these factors constantly go on decreasing.
Various gadgets used in houses; factories and vehicles contribute to increase of heat.
Due to such factors, some climatologists believe that heat island effect, which means
an increase of heat from the surrounding open country, has already taken place in
Dhaka city. In fact, any person moving from the bank of the river to congested old
Dhaka through busy markets to the less congested northern part might experience
77
numerous microclimates with differing temperature and humidity is now a common
experience.
Table: 4.3
Name of
the
researcher
1.
Karmokar
et. al’s,
1993
Karmokar et. al’s research methodology and findings.
Methodology
Findings
Study on the basis of about
30 years (1960-1990) data
regarding variability and
probabilistic extremities of
climates elements in Dhaka
researcher
made
the
observations of the findings.
(a) The mean temperature increases
from January to April, then remains
almost constant up to September, and
decreases up to January. The mean
minimum temperature is the lowest in
January, increases up to June and
remains fairly constant up to
September and decreases after that.
(b) The mean prevailing wind speed
is minimum in January and maximum
in April (No mention of directions).
(c) The mean rainfall increases
sharply from January and attains
maximum value in June and July,
after which it decreases.
(d) The mean relative Humidity has
higher values during the southwest
monsoon and then decreases sharply
up to March.
(e)The months of December, January
and February are the most
comfortable months in Dhaka, where
as April through October are
uncomfortable months.
78
Table: 4.4
Name of the
researcher
2. Hossain et
al’s
Hossain et al’s research methodology and findings.
Methodology
Findings
Discomfort
Index
for
measuring climatic comfort
Discomfort Index (D,I.)
was suggested by Thom's
as:D.I.= 0.4(Td +Tw)+15,
Where Td and Tw, stand
for Dry bulb and wet bulb
temperature respectively in
°F scale. In °C scale it
comes to be, D.I.= 0.72 (Td
+ Tw) + 40.6. The comfort
situation of Bangladesh in
terms of Discomfort Index
(D. I.) has been expressed
as the result of findings.
(a) MARCH TO MAY: At 6.00 AM
BST (Bangladesh standard time), for
whole Bangladesh is generally
comfortable. Evening Hours 6.00
PM BST Dhaka and northern half of
Bangladesh is generally comfortable.
In April, rest of the country falls
below discomfort zone with D.I value
exceeding 75.
(b) JUNE TO SEPTEMBER: At 6.00
AM BST for whole Bangladesh is
generally below discomfort. The
weather is hot and dry. 6.00 PM BST
for whole of Bangladesh is below
discomfort zone.
(c) OCTOBER TO NOVEMBER: At
6.00AM BST for whole Bangladesh
is generally under discomfort zone
and At 6.00PM is below partial
discomfort.
(d) DECEMBER TO FEBRUARY:
6.00 A.M BST: In January and
February Dhaka is below comfort
zone. 6.00 P.M.: Dhaka is below
comfort zone.
Note: For more details see appendix E.
79
Table: 4.5
Name of
the
researcher
3. Hossain
et al’s,
1991-1992
Hossain et al’s research methodology and findings.
Methodology
Findings
Study on general climate on
the basis of 40 years (19511990) climatic data of Dhaka
city researcher has prepared
the findings.
(a). After sunrise, the day
temperature increases at attains
maximum value at 3.00 P.M. BST.
The day temperature in urban area is
higher than sub-urban and rural
areas. The night temperature in
rural areas is lower than urban areas.
(b). The relative humidity decreases
at daytime and increases at night,
the minimum value being at 3.00
P.M. BST, when the day
temperature is maximum.
(c). Urbanization has profound
effect in reducing the wind speed.
(d). The heat island effect is less
prominent, the intensity being 2.5º
in April and 0.6º in July. The less
prominence is due to high humidity
and surface wind.
(e) Relative humidity is found
inversely related to the local
intensity of urban heat island in
Dhaka.
(f) Total incoming solar radiation in
Dhaka city is found about 12%
lower than that in the rural areas.
(g) The amount of precipitation is
higher in Dhaka city except in
August.
Note: For more details see appendix E.
80
Table: 4.6
Name of the
researcher
Khaleque et. al’s research methodology and findings.
Methodology
4. Khaleque Study on Micro-climate of
Dhaka city: One group of
et al’s,
researchers on the basis of
1993
their studies on Temperature
and Humidity conducted in
10
points,
viz.
(01)
Agargaon, (02) tejgaon, (03)
Motijheel,(04) Dhanmondi,
(05)
Nawabgonj,
(06)
Mirpur, (07) Kallyanpur,
(08) Gulshan, (09) Bakshi
bazaar and (10) Airport,
commented.
Findings
(a)
During
winter
month’s
maximum intensity of heat island
in the order of 3.8° C is observed.
(b) Two peaks of heat island
intensity are observed one at early
morning and another early night,
but the early morning heat island is
stronger.
(c) The heat island or warm
pockets found over the densely
populated residential and high-rise
building construction area. The
cool areas are found over the well
ventilated
planned
residential
areas.
(d) During summer months heat
island effect is insignificant.
(e) Humidity island has an inverse
relation to heat island whenever
moisture is less, but lower heat
island intensity whenever moisture
is high.
Note: For more details see appendix E.
4.5
Climatic Comfort
The ambient environment has both physical and environmental effect on
human being and is therefore of' principal importance in building design. One of the
architects/designers main tasks is to create a comfortable environment inside the
building, which is appropriate for all the human activities likely to take place there.
It is a challenge for the designers to strive towards the optimum of total comfort,
81
which may be defined as the sensation of complete physical and mental well being
(Koenigsberger et al 1973; Goulding et al 1992). Thus defined, it is only to a limited
extent within the control of the designer. The occupants' physical, biological, and
environmental characteristics also come into play. The individual members are
unlikely to be satisfied concurrently.
Although, the notion of a comfortable
environment for all would encompass the consideration of individual preference, still
there are a set of general conditions in which a majority of people would feel
comfortable where the determinants are air and radiant temperature, humidity,
airflow etc.
4.6
Definition and Concepts of Comfort
Comfort is not completely a sensory phenomenon but largely one of
perception (Fisher, 1978 (Bansal, 1994). While sensations like smell, sound, light,
temperature and pressure being at physiological level, the experiences do not
conclude at sensory level, but at the level of perception.
Perception of these
individual sensations are often subjected to short as well as long term conditioning,
caused by a wide range of influences. These influences may be developed from
psychophysical to socio-culture framework of an environment.
Therefore,
disparities in comfort perception are observed among the rural and urban population
and among developing and developed countries (Ahmed, l995).
Comfort is generally defined in terms of a number of environmental factors
like air temperature radiant temperature, airflow, relative humidity and their effect is
synergistic thermal comfort can be defined operationally as the range of climatic
conditions comfortable and acceptable inside buildings. It implies an absence of any
of thermal (heat or cold) discomfort (Givoni, 1998).
The definition of thermal comfort emphasize on the notion of thermal
neutrality i.e, the conditions under which the human body is in a state of thermal
equilibrium with its surroundings (Fanger, 1970; Burburry, 1983; Edholme et at
1985). But attainment of neutrality does not necessarily ensures comfort. For
82
example, a person who is exposed to an asymmetric radiant field may well be in
thermal neutrality but is unlikely to comfortable. In most situations encountered in
buildings, however, the two conditions will coincide (Goulding et al, 1992).
According to American Society of Heating, Refrigerating and AirConditioning Engineers (ASHRAE) after an extensive study defines thermal comfort
as that condition of mind, which expresses satisfaction with the thermal environment
(ASHRAE, 1958). Factors associated with olfactory, acoustic and visual
environment can considerably influence thermal comfort judgment (Nanda, 1989;
Ahmed, 1995)
The effects of different climatic variables on human comfort have been
slowly recognized through ages. The effect of temperature on human comfort was
mentioned by Vitruvius (Vitruvius, 1931) in the first century B.C. Leonardo Da
Vinci recognized the influence of Humidity in the fifteenth century. In 1733 John
Arbuthnot published "An Essay Concerning the Effect of Air Movement on Human
Bodies". Thomas Tredgold in 1824 in his book "Principles of Warming and
Ventilating Public Buildings, Dwelling Houses, etc." pointed out that the people
could be comfortable from the radiant heat of an open fire even when air temperature
was too low for comfort (Cowan, 1983).
4.7
Previous Researches on Indoor Comfort
The combination of temperature, humidity and air movement that gave equal
sensations of comfort was than designed as having the same effective temperature
(ET). The effective temperature is the dry bulb temperature in which group of equal
comfort sensations at which the relative humidity is 100% and air movement is zero
(Cowan, 1983; J.E.Hill, 1975) along with other climatologists prepared a
comparative study of various thermal indices and calculated their range of
application as shown in (Table 4.5).
83
Table: 4.7
Comparative study of various thermal indices and calculated their
range of application
Source: Cussed, Liz, Howell: A Proposed Concept for Determining the Need for AirConditioning Buildings Based on Building Thermal Response and Human Comfort. NBA.
Washington.
The experiments determining Effective Temperature (ET.) have been
progressively refined. The current standards are based on experiments carried out
under the auspices of ASHRAM at, Kansas University and published in 1973 (F.H.
Rohles, 1973). These experiments were conducted on college students wearing
clothing equivalent to 0.6 clo and sitting in the test room without doing any work.
The mean radiant temperature (MRT) was equal to the dry bulb temperature and the
air velocity was low, less than 0.17 m/s. The main variables were temperature and
humidity. The comfort zone as described by the subjects during the experiment was
then traced on a Psychometric Chart. The recommendation of the ASHRAE comfort
standard is limited between relative humilities, 60% and 20% and by the dry bulb
temperatures, 22.8° C and 25° C.
In 1975, energy conservation measures higher design temperatures were
recommended for summer, and lower ones for winter (Cowan, 1983). At this stage
the winter temperature was still considerably higher than that considered appropriate
in England before the energy crisis of 1973. The preferred range of temperature for
the British House of Commons in 1840 was 11° C to 22º C. Sir Douglas Galton in
his article on "Heating" recommended a temperature range for living room as 12° C
to 20° C and a temperature for bedrooms not less than 4° C (Encyclopedia, 9th
Edition,1880). Dr. Thomas Bedford conducted an inquiry in 1940 and recommended
84
a temperature range on 19.5° C to 20º C, which was found to be satisfactory.
Differences in comfort vote are due to the differences in amount of clothing
customarily worn and this varies with time and place; but they also reflect different
conceptions of comfort.
On the basis of 40 field studies conducted in a wide range of climatic
conditions Humphrey's (Humphreys, 1975) commented that neutral temperatures Tn
for adults range from 17° C to 35º C, depending on the mean temperature
experienced by the population, suggesting that acclimatization indeed affects the
temperature required for thermal neutrality. Normally band of 4° C (-+ 2° C)
centered on Tn comprises the comfort zone. If Tm is the mean temperature, then Tn
may be predicted from the equation:
Tn = 2.56 + 0.831 Tm (°C)
The standard error of prediction considered was 1.1º C. It is possible to
predict Tn for each month of the year by examining the average temperatures Tm for
the climate in question. The Neutral Temperature Tn and Comfort Zone in Dhaka
city for the hot months (April, May, June, July, August, September, October) for
twenty years average readings based on Humphrey's' equation was calculated by one
researcher (Ahmed, 1987). This has been presented in the (Table: 4.6).
Table 4.8
Discomfort index for Dhaka
HUMPHREYS MONTHLY NEUTRAL TEMPERATURE AND
COMFORT ZONE IN DHAKA IN 1987
MONTH
AVERAGE TEMP.
HUMPHREYS NEUTRAL TEMP
COMFORT ZONE
Tm°C
Tn°C
ºC - ºC
April
29.0
26.6
24.6
28.6
May
28.9
26.6
24.6
28.6
June
28.5
26.3
24.3
28.3
July
28.6
26.3
24.3
28.3
August
28.6
26.3
24.3
28.3
September
28.7
26.4
24.4
28.4
October
27.2
25.1
23.1
27.1
Source: Ahmed, ZN. 1987, unpublished M. Phil. Thesis on The Effects of Climate on the
Design and Location of Windows for Buildings in Bangladesh.
85
It may be relevant to summarize the findings of experiments regarding
comfort temperature in various periods and regions and to compare those against the
temperature and humidity of Dhaka city of contemporary period in the hot months.
The comparison has been presented in Table 4.7.
Table 4.9
Previous study of Indoor
ndoor comfort temperatures
REFERENCE
COMFORT TEMPERATURE
OTHER FACTORS
UNDER CONSIDERATION
01.British House of Commons
Recommendations 1840
02.Encyclopedia Britannica 1880
11° - 22° C
Not mentioned
12° - 20° C
Not mentioned
22.8° - 25° C
Rel. Humidity 60% - 20%
19.5° - 20° C
Not mentioned
27° C
At R.Humidity 80%,
03.ASHRAE comfort Standard
of 1974
04.Dr. Thomas Bedford 1940
05.ASHRAE experiment in
Singapore 1952
air velocity 0.4 m/s.
06.Humphrey's neutral Temp. Tn
15°-37°
Requires acclimatization
17° - 35°C ((based on 40
and variation of clothing
field studies)
and take into account
human behavioral
adaptations
07.Neutral Temp. for Dhaka
23.1º- 28.6º
Same
21.0-30.0
At R.Humidity 70%,
17.0-32
At R.Humidity 25%-80%,
24.0-32.0
At R.Humidity 50%-95%,
calculated by Ahmed on
Humphrey's Equation
(Average of April-October
Months) Tn 26.46°
08. Sharma & Ali (1986)
Summer season
09. Sharma & Ali (1986)
Winter season
10. Mallick (1994)
Summer season
still air condition
86
4.8
The Indoor Comfort Zone
The concept of comfort zone within all ambiences is described with respect
to a combination of environmental variables where a majority of people may feel
comfort. By virtue of this zone, comfort condition can be expressed in terms of
combination of factors like temperature, relative humidity, airflow etc. instead of a
single parameter, (Ahmed, 1995).
The ASHRAE comfort zone is drawn on a conventional psychometric chart.
It specifics boundaries of air temperature and humidity for sedentary people. It was
constructed mainly for use in air-conditioned office buildings but is also used in
evaluation indoor climates in residential buildings (Givoni, l998). Although the
psychometric is suitable to describe comfort condition where skin wetness is
important factors. It has limitation in humid conditions where higher velocity of air
is accepted and acclimatization is an important determinant (Ahmed, 1995; Olgay,
1963) first developed a bioclimatic chart below where the notion of comfort zone is
defined in terms of dry bulb temperature as ordinate and abscissa respectively.
The comfort zone is plotted on a chart. It is bounded by a fixed lower
temperature (21°C) and by a humidity dependent upper limit. At relative humidity
below 50 % tile upper comfort limit is 27.8 ºC. At relative humidifies above 50% the
upper temperature limit drops down gradually, until it intersects with die lower limit
at 90 % relative humidity (Givoni, 1998). Later the chart was modified by, Szokolay
(1984), Arens (1980) and Givoni (1982). Sharma and Ali (1986) in their study of
Indian subject suggested temperatures above 30ºC for comfort although upper limit
of relative humidity are restricted to 70 % (Mallick,1994) has developed summer
comfort zone for Bangladesh. For winter after Givoni (Figure 4.2), Sharma and Ali
suggested the temperature range for winter is from 17 ºC to 32 ºC while humidity
range is fixed in lower limit 25% to upper limit 80% (Mallick, 1994; Abu Mukim,
2002). According to Mallick for summer comfort temperature range is, the lower
and upper limit of comfort temperature is 24 ºC and 32 ºC while humidity ranges,
between 50% and 95%, in a condition with no air movement.
87
Figure 4.2
climate.
Olgyay’s Bio-climatic chat and Adaptation of comfort zone in warm
88
4.8.1
Summer Comfort Zone
The evaluation of comfort conditions is based on the analyses of air
temperature and relative humidity values. According to the research conducted by
Mallick (1994), air temperature for comfort with no air movement and for people
wearing normal summer clothing, engaged in normal household activity indoors are
within the range of 24 ºC and 32 °C and for relative humidity between 50% and 95%.
In still air condition people feel comfortable even in higher humidity, which is
expected response in a location where humidity is generally high for most of the
years. With the introduction of airflow relative humidity up to 95% is tolerated.
Little or slow air movement up to 0.1 -5.0 m/s makes very little difference to
comfort temperatures. The mean comfort temperature for, this range is 28.9ºC. For
higher velocities of 0.3 m/s to 0.45 m/s the upper and lower limits of comfort
temperature increase between 2-3 °C and mean comfort temperature increases to
31.2ºC. Summer comfort zone for Bangladesh is derived from the above findings,
which taken into account the climatic features like, air temperature, relative humidity
and air movement.
Figure 4.3:
Summer comfort zone for Bangladesh (after Mallick. 1994)
The lower and upper limit of comfort temperature is 24 ºC and 32 ºC while
humidity ranges, between 50% and 95%, in a condition with no air movement. The
regime of comfort temperature increases (higher limit) with the introduction of
89
airflow. People feel comfortable above 34 ºC with the introduction of air flow at the
rate of 0.30 m/s. Tolerance temperature can further increase to near 36 ºC with air
flow at the rate of 0.45 m/s.
The summer comfort zone (24 ºC- 34ºC; humidity range is 70%) Figure 4.3
as developed by Mallick (1994) and winter comfort zone (17ºC- 32 ºC; humidity
range is 25% -80%) was developed by Sharma and Ali (1986), are adapted as a
reference for comfort judgment and evaluation of thermal performance of traditional
house in Bangladesh at Dhaka during summer and winter season.
4.9
The Outdoor Comfort
The comfort criteria used in the evaluation of the urban microclimates was
based on survey in the hot and wet summer conditions in Dhaka. Survey results also
include significant number of instances with ambience at close to skin temperature
and relative humidity, corresponding with the hot-dry seasonal conditions. However,
comfort regime for the winter months has not been considered, as the persistent
environmental concern in the warm humid climate of Dhaka is overheating. The
following criteria for outdoor comfort in Dhaka city can be identified. Research on
outdoors comfort has been done by Sabbir Ahmed in 1995 in his PhD.
4.9.1
Air Temperature
The upper threshold of comfort air temperature for outdoors, under shade, is
32°C, under still conditions with 70% relative humidity. Beyond this temperature
the number of people dissatisfied with the ambience will progressively increase. The
average outdoor comfort temperature is 30.25°C = 30° C. The acceptable fluctuation
temperature around the comfort value for long stay spaces (such as chowk, squares
etc) is ±3°C and for short stay or transient spaces (such as streets) it was ±1°C.
90
4.9.2
Radiation
In almost all the situations observed, a significant number of' comfort votes
were associated with shaded conditions. For urban conditions solar shading is a
prerequisite to comfort. However, with increased air flow (1.5 m/s or above) and
ambient temperatures at 32°C or below, conditions of comfort have been reported
under exposed conditions. Radiant temperature is an effective descriptor of outdoor
comfort. The globe temperature range for comfort is between 28.7°C to 32.6°C with
an average relative humidity of 70%.
4.9.3
Relative Humidity
Tolerance to high relative humidity was observed to be notable in all cases.
In a number of instances, adaptation (i.e. reporting comfortable) to relative humidity
between 70% to 80% was observed in situations without airflow. Airflow with 2 m/s
velocity was observed to increase the tolerance to relative humidity as high as 95%.
Under still conditions relative humidity varying between 50% to 60% was associated
with comfort votes at air temperature between 32°C to 33.5°C.
4.9.4
Airflow
One of the most important contributors to outdoor comfort is airflow. The
significant effect of airflow is indicated by the increase in the number of people
thermally satisfied with an ambience, but without increasing the upper boundary of
comfort air temperature. Air velocity as low as 0.5 m/s contributes to the comfort
outdoor particularly under shaded conditions. It has been observed that the tolerance
to high relative humidity is considerably increased with air velocities above 1.0 m/s.
With regard to outdoor conditions, the cooling effect caused by airflow outweighs
the disturbance caused by high air velocities, such as hair blown, pressure against
face etc.
However, with air temperatures above 33°C, increasing air velocity
91
significantly reduces the number of people thermally satisfied with the ambience.
Therefore, during the periods with high ambient temperature, i.e. In the hot and dry
season (covering the months March, April and May), still and shaded conditions may
be favored against turbulent conditions with air temperatures at or above skin
temperature.
4.9.5
Comfort Zone for Outdoors
The comfort zone (in shade) shown in Figure 4.4 is derived by Sabbir Ahmed
in 1995; the field study conducted in summer conditions, hence the lower threshold
(i.e. minimum Temperature).
Figure 4.4:
1995).
Summer comfort zone graph for outdoor comfort (Sabbir Ahmed,
For comfort may vary in the winter season due to seasonal adaptation. The
zone is derived for people involved in activity of I Met, wearing 0.35-0.5 Cloy under
shaded conditions. The shaded area outlines the comfort zone under still conditions.
92
The comfort zone indicates the influence of airflow increasing the tolerance to
higher relative humidity.
4.10
Conclusion
This chapter on previous study of climate at Dhaka city has discussed in
general various aspects of climate including factors of climate, micro climate,
historical study on climate in Dhaka city, various factors responsible for climatic
comfort, etc. Most of the studies have been carried out by the climatologists, who
are mostly concerned with a climate of a large area. Some of the studies by the
climatologist revealed that numerous micro climates have already been generated in
Dhaka city and that the climates in these pocket areas widely varied from the rest or
adjacent areas. In urban areas it is a great problem especially in congested busy
cities micro climates vary quite rapidly. The construction of each building in a dense
area being about new change in micro climate due to its presents and associated
activities. The findings of the section have helped to develop an understanding of
the factors related to indoor comfort as observed in summer and winter condition in
Dhaka city and identifies a range for thermal comfort for indoor environment. Based
on the study of all researchers’ common observation, the following conclusion can
be drawn.
• April is the hottest month of the year
• January is the month of lowest temperature
• From April to October month the air temperature is uncomfortable.
• From June to September month the air temperature remains constant.
These findings form the basis for the evaluation of the thermal performance
of the traditional house in Bangladesh is presented in the next chapter.
CHAPTER 5
METHODOLOGY
5.1
Introduction
The arrangement of urban conditions of Dhaka is distributed over a
combination of natural and man-made landscape. This provides large opportunities
to study the complex of urban microclimates. Their effects are largely controlled by
local events. Therefore, it is not possible by regional climatic studies to register such
transient phenomena.
This study deals with the thermal performance of traditional house roof
section of Bangladesh with the special reference to Dhaka. A field study was
essential to evaluate the relationship between upper space and indoor comfort.
The following sections present the methodology of the fieldwork on thermal
performance of the traditional upper space carried out in a traditional house of
Bangladesh located in Dhaka city. The findings in this fieldwork are used for
analyzing the indoor climate of traditional houses of Bangladesh.
94
The Site
Figure 5.1:
Location of Test house area (Gulshan) in Dhaka city Map
Test House
Figure 5.2:
Physical condition of Test house area (Gulshan) in Dhaka city
95
5.2
Objective of the Field Study
It is a common practice in Bangladesh particularly among architects and
environmental engineers to use data recorded at the meteorological station for design
purpose. It is evident from the field study performed in Dhaka, that indiscriminate
use of meteorological data in the context of Dhaka city, of a considerable size and
diverse texture, is inherently inaccurate (Sabbir Ahmed, 1995; Bijon Behari Sharma,
2002; Abu Mukim Mirdha, 2002).
The environmental data recorded at the
meteorological station are affected by characteristics of that particular observation
site. Such measurement does not always account for the various characteristics of
the different urban sites, often leading to distinct micro-climates.
applicability for design purposes can be considerably limited.
Hence their
Although
environmental factors, such as relative humidity, radiant temperature and air flows
are indicative of these variations in the urban climate. Site air temperature has been
found to be the most notable indicator. This phenomenon has been demonstrated in
chapter six of this research. For this reasons this research’s field study decided to be
done on site physical measurements. The field study and the subsequent results were
based on the following objectives:
•
To record primary environment data in test house traditional house in
reference to the microclimate of the Dhaka city.
•
To understand the thermal performance of the traditional house by the
influence of the upper space.
•
To evaluate the indoor environments in terms of indoor comfort requirements
to judge the performance of the upper space in the test house.
5.3
Historical Background of the Test House
The test house was first built at the rural area Maowa in Bangladesh, 1955.
In rural area it was in a courtyard arrangement with other four units in one boundary.
The surrounding was open planning which provided cross ventilation. The selected
96
room which is master bed room has two doors, one was towards a courtyard and
another was towards kitchen units and toilet. But when the owner migrated to Dhaka
city, he then brought one unit house and rebuilt it Gulshan area. In Dhaka, the
surrounding situation changed for the density, lack of privacy, lack of safety and
security. According to their demand they extended the living space after ten years of
rebuilding.
Figure 5.3:
Traditional house (test house) in dense Gulshan area.
Figure 5.4:
Same type of traditional house in rural area Maowa
97
5.4
Selection of the Particular Test House
The primary criteria for the selection of the test house of the Bangladesh
traditional house are as follows,
•
Traditional house is effectively designed to establish approach towards
sustainability of worst urban environment.
So the test house which is
selected for this research is situated in the urban context in Dhaka city at
highly dense Gulshan area.
•
To justify the performance of the traditional house in an extreme
surroundings conditions within a urban micro climate.
•
53 years ago this house was built in rural area (Maowa, Bangladesh), 1955.
In 1975, the owner when migrating to at Dhaka city, brought this one unit
house and rebuilt it at Gulshan area. So there is no doubt that the particular
test house is the most appropriate as a traditional house, which have all
features of the traditional houses in Bangladesh.
5.5
Description of the Test House
The test house is surrounded by similar type of traditional house on the north
and south side within 0.6m and 1.5m gap at respective orientation. The west and
east sides are facing a 1.5m road.
98
Birds eye view of the surroundings of the Test House
A
Figure 5.5:
3.3 m
7m
Corrugated Iron Sheet
3.6 m
Test room
bedroom
bedroom
Wooden post ( .15m X .15m)
1.2 m
.6 m
Wooden Floor ( .37m thick, )
HOBO Data Logger
1.8 m
HOBO Data Logger
Sensor
A
N
Figure 5.6:
dining area
living area
Plan of the Test House
For collecting the indoor data the bedroom was selected which is occupying
the southwest corner of the house. The room height is 2.8m. The size of the
bedroom is 3.3m wide by 3.6m length. This room has two windows of 1m wide on
west and east side periphery and two doors. This room is connected to living area
through a door.
Walls are made with 150mm by 150mm wooden post and
corrugated sheets. The ceiling is made of 37.5mm thick wooden planks with 125mm
by 75mm wooden beams. Furniture of the room consists of a wooden double bed,
99
wooden wardrobe, wooden cabinet and a wooden study table with chair. The floor is
raised from the ground and made by wooden planks.
There are two 60 watt
florescent lights (one is regularly used and other is occasionally used) and one
ceiling fan in the test room.
Figure 5.7:
Interior of the Test House
There is another consideration in the selection of the test room. In the house
there are another two rooms, which are one small bedroom and one small living area.
The other bedroom is at the north side of the house and the living area is at the east
side. The selected test room is located at the southwest corner, which is the hottest
corner of the house according to user experience. The selected room receives solar
radiation for a longer period compared to other two rooms and also from a study of
Sharma, 2002 has been found that the relation between hot category rooms and
cardinal locations, the west side room took the highest position and southwest room
took the 2nd highest position in Bangladesh. This research selects the worst corner of
the test house to justify the thermal performance of the traditional house in
Bangladesh.
The outer surface of the upper space is made of corrugated iron sheets. It is
directly exposed to the sun. The extended roof protects the windows of upper space
from sun and rain. The upper space has four windows on west and east wall, which
are 1.25m by 1m wide. The window of north and south side of the upper space is
closed. The floor of the upper space is of wooden planks. In this area there is an
100
incandescent light, which is used occasionally. Generally upper space is used as a
store.
5.6
Instrumentation
Data loggers were installed in the test house for collection of air temperature
and relative humidity data. The remote data loggers recorded indoor air temperature
and relative humidity with the help of external sensor.
Thermal Data Logger and sensor
Figure 5.8:
External sensor of thermal Data Logger
Thermal Data Logger position in upper space and placement of
external sensor
Outdoor air temperature, humidity and upper air temperature and humidity
are also taken by the sensor of data loggers. Data were recorded at interval of five
minutes. The controlling software assigns range of the logger interval. The loggers
are initiated by software Box Car Pro 4.0.
The software is required for the
downloading of data from the data loggers and making the graph; exporting data to
excel file. Excel software was also used for data analyses.
101
Figure 5.9:
Thermal Data Logger position in upper space (left) and windows of
upper space (right).
The instruments used in field study were as follows
Thermal Data Logger (HOBO H08-007-02)
2 Nos.
External Sensor TM C6-HA
3 Nos.
USB cable
1 No.
The sensitivity of the manufacturer’s calibration of the data loggers were
compared with the metrological recording (under similar condition) in Agargaon
Metrological Office and found to be satisfactory.
A
102
3.3 m
7m
Corrugated Iron Sheet
HOBOData Logger
Tu
Wooden post ( .15m X .15m)
.6 m
HOBO Data Logger
Living area
2.8 m
Ti
To
Wooden Floor ( .37m thick, )
1.2 m
Upper space
Ceiling ( wooden plank .37 mthick)
5.76 m
bedroom
1.0 m
1.2m
3.6 m
Test room
bedroom
1.05 m
Upper window
Corrugated Iron Sheet
Test room
HOBOData Logger
Sensor
Corrugated Iron Sheet
Wooden post ( .15mX .15m)
Wooden Floor ( .37m thick, )
dining area
living area
A
N
0.45 m
1.8 m
HOBO Data Logger
Sensor
Figure 5.10: Thermal Data Logger position in indoor, upper space and outdoor in
test house plan and section
5.7
Installation of the Thermal Data Loggers
The thermal data loggers and sensors were installed in the test house in three
areas. One data logger (no.1) with two sensors was used for indoor and outdoor data
collection. Another data logger (no .2) with one sensor was placed in the upper
space for collecting data.
Sensor indoor
Thermal data
logger (no 1)
Indoor
Figure 5.11
Sensor outdoor
Sensor upper space
Thermal data
logger (no 2)
Upper space
Use of thermal data logger and sensors.
A thermal data logger and one sensor were used for collecting indoor data
(figure 5.11). Data and readings from one sensor and machine in indoor space are
generally the same. So for this research, sensor data (C*4 series, see appendix D)
was used for analysis.
103
Another sensor of the thermal data logger (no 1), which is placed in outdoor,
was used for outdoor data collection. This sensor was hanged to avoid any contact
of the wall surface and placed under shaded area for the protection from direct
weather effect during the data collection period. So for the outdoor only one data
(C*3, see appendix D) is used.
Another thermal data logger with one sensor was placed in upper space for
upper space data collection (figure 5.11). Data and readings from one sensor and
machine in upper space are generally the same. For this research sensor data (C*4,
see appendix D) series is used for analysis.
Position of one data logger and sensor in the upper space is at 1.2m from the
wooden ceiling level (figure 5.10). Thermal data loggers were mounted to the
wooden post with the help of hook, nails and steel net.
In the indoor, the data logger was hooked at 2.4 m from the floor level to
record immediate changes occurring between upper space to indoor space air
temperature (figure 5.9).
5.8
Methodology of Data Collection
The fieldwork was conducted in a test house of the Bangladesh traditional
house, which is located in the Dhaka city at the dense Gulshan residential area. Data
was taken for the most persistent and dominant two seasons are winter and summer.
At the same time the most extreme climatic value are registered during these periods.
General climatic conditions of the observation period is described the below table
5.1.
104
Table 5.1:
The seasons and months of Bangladesh with climatic condition
Dominant
Season
Gregorian Calendar
Months
Meteorological Seasons
Climatic
Condition
Summer
March
April
May
June
Pre-monsoon
Pre-monsoon
Pre-monsoon
Monsoon
hot-dry
hot-dry
hot-dry
hot-wet
Winter
January
February
Winter
Winter
cool-dry
cool-dry
From previous study it was identified that January is the coolest month and
April is the hottest month for Bangladesh. The mean maximum temperature over
Dhaka has its lowest value in January and progresses as the season progresses. It
becomes maximum in April with a decreasing tendency up to August. The mean
temperature increases from January to April, then remains almost constant up to
September, and decreases up to January. The mean minimum temperature is the
lowest in January, increases up to June and remains fairly constant up to September
and decreases after that (Karmokar et. al, 1993). Winter period in Bangladesh is
from December to February only for three months. For this reason in this research
the field study is carried out for winter in the month of January and February. For
the long summer season the selected month is March to June because April to
September remains almost constant.
Climatic data were collected by the help of HOBO thermal data loggers and
sensors for six months. To verify the air temperature of Dhaka city, five days data
was taken per minutes and was found that within eight to ten minutes air temperature
has no change (see in appendix D)..
For this reason data logger has been
programmed to collect data every five minutes interval. With this interval, the
loggers can take seven days data and 2030 nos. temperature and humidity data. For
that reason the collected data was downloaded after six or seven day’s interval from
105
the thermal data loggers. Data collecting was started from 10 January 2007 and it
was continued up to 20 June, 2007.
Hence, addressing environmental issue of these periods in terms of studying
thermal performance of the Bangladesh traditional house upper space. Following
details were obtained from the occupants of the traditional house.
•
The upper space is used normally as store. During winter season (January
and February) the weather is cold and dry, all the windows of the upper space
are closed for the protection from cold wind flow. From the practical use it
was found that if windows remain close in the winter season, indoor becomes
warmer than the outdoor air temperature.
•
In summer period (March to June) the weather is hot dry and hot wet.
According to user, during this time, all the windows of the upper space will
remain open for cross ventilation and for that reason the temperature of the
upper space and indoor living space remain less than the outdoor temperature.
In this research, the field study of this phenomenon is observed to justify the
thermal performance of Bangladesh traditional house’s upper space during
winter and summer season.
This research also verifies the thermal performance of the upper space. In
order to analysis the thermal performance the following methods were used for data
collections.
The percentage of opening of the upper space is different in different month.
Observation on environmental factors relate directly to thermal behavior of indoor
environment, air temperature and relative humidity.
106
Table 5.2:
Tabular output method of Climatic data for the test room of the
traditional house
Season
Winter
Month
Date
January
10th to
31st
1st to
28th
February
March
Summer
April
May
June
1st to 31st
1st to
30th
st
1 to 31st
1st to
20th
Collected Data ( Air Temperature)
Indoor
Upper(attic)
Outdoor
( Ti)
(Tu)
(To)
Indoor
Relative
Humidity
Opening of
window in
Attic
Ti
Tu
To
Rhi
0%
Ti
Tu
To
Rhi
0%
Ti
Tu
To
Rhi
0%
Ti
Ti
Tu
Tu
To
To
Rhi
Rhi
25%
75%
Ti
Tu
To
Rhi
75%
Figure 5.12: Window opening 25% of the upper space during construction (right
top) and 75% window opening (left bottom).
107
Corrugated Iron Sheet
HOBO Data Logger
Living area
2.8 m
Ti
To
Ceiling ( wooden plank .37 m thick)
5.76 m
Upper space
1.05 m
Upper window
1.0 m
1.2m
Tu
Test room
HOBO Data Logger
Sensor
Corrugated Iron Sheet
Wooden post ( .15m X .15m)
0.45 m
Wooden Floor ( .37m thick, )
Figure 5.13: Position of the Data loggers Ti = Temp indoor, To= Temp outdoor,
Tu = Temp upper space
5.9
Impact of the surrounding
The test house is densely surrounded by other traditional houses.
The
distance between other surrounded houses are East - West side 1.5m and NorthSouth side 0.6m. Temperature, humidity and wind velocity also varies depending on
the density of the surroundings built forms (Ahmed, 1995). Wind velocity does not
affect the indoor air temperature because of high density of the built forms. Highest
wind speed occurred in April 2.9m/s while lowest was November 1.3 m/s. The
prevailing wind direction was same as for last thirty years. Urban, suburban and
rural relative humidity exhibits a marked diurnal variation and generally decreases
towards city center.
108
During the afternoon in the dry seasons the difference may be as high as 12%
(Ogunloyinbo, 1984) and night temperature difference can be as high as 13% in the
same seasons.
Location of the test house
Figure 5.14: The site and surroundings of the test house and distance from other
houses
109
Rapid urbanization after 1980 plays a vital role in the reduction of wind
speed in Dhaka city (Sabbir, 1995). According to the above consideration, it is
identified that the wind speed does not affect the thermal performance of the
traditional house in this dense surroundings. Indoor cross ventilation does not work
successfully
Therefore, the wind velocity was not measured for this research. The reading
of the BMD data has shown variation in temperature data (1.47ºC to 3.09ºC)
difference from the field study temperature data. Furthermore, observation made by
Karmakar and Khatun (1993) and Hossain and Nooruddin (1993) indicates that
because of inexorable urban growth in Dhaka a noticeable variation is observed in
temperature in different part of the city. Sharma (2002) indicates the existence of
further micro-climate variation in the same locality.
5.10
Conclusion
The topics discussed in this chapter include methodology and the field study
procedure. There include how the various readings were taken and recorded, how
the data and information were transformed into tables and graphs to present
comprehensive picture of the findings. These findings and information shall be
analyzed in the following chapter for a better understanding of the thermal
performance of the traditional house in Bangladesh at Dhaka city.
CHAPTER 6
PERFORMANCE OF TRADITIONAL HOUSE AT DHAKA CITY
6.1
Introduction
This chapter discusses the result of field study on the comfort and to
evaluate thermal performance of traditional house in Bangladesh. The field study
were obtained for two different major climatic seasons prevailing in Bangladesh.
The intent of this field study is to justify the thermal performance of upper space
and the indoor living area of traditional houses in Bangladesh. In the evaluation
process, certain environmental criteria, which are directly influenced by the upper
space air temperature difference with indoor and outdoor in the test house, have
been considered. Indoor temperatures were compared with outdoor temperature to
evaluate the impact of the roof design on the internal thermal heat gains.
6.2
Comparative study of Field Measurement and Meteorological data
A comparative study was done between outdoor temperature of the field
measurement and Bangladesh Meteorological Department (BMD) data for Agargaon,
at Dhaka.
The evaluation is made on the basis of daily average of the field
measurement of outdoor temperature and daily average of the Bangladesh
111
Meteorological Department’s data. The comparisons were made for selected 10
days during each winter and summer seasons.
6.2.1
Winter Season
23.00
22.40
22.21
22.00
22.15
21.59
21.48
21.54
21.13
21.00
20.56
20.56
Outdoor Temperature ºC.
20.30
19.77
20.00
19.00
20.08
19.99
19.84
19.84
18.94
18.75
18.65
18.50
18.48
17.98
18.00
17.16
17.00
16.00
15.00
14.00
17-Jan
18-Jan
19-Jan
20-Jan
21-Jan
22-Jan
23-Jan
24-Jan
25-Jan
26-Jan
27-Jan
Days
Weather office data
Figure 6.1:
Field study data
Profile of daily average temperature of meteorological office data and
field study data of same days in winter season
The sensitivity of the manufacturer’s calibration of the data loggers were
compared with the meteorological department data recording in Agargaon
Meteorological Office and was found to be satisfactory. But on the site where the
data loggers were installed the outdoor air temperature varied from 1.47ºC to 3.09ºC
temperature difference and average temperature difference is 11% high from the
reading of the meteorological department record data at the same day.
112
6.2.2
Summer Season
31.00
29.00
27.86
27.08
27.00
Outdoor temperatureºC
24.95
25.00
24.40
24.72
24.91
27.25
26.39
26.15
24.95
24.50
23.57
23.10
22.63
23.00
23.01
22.18
22.14
22.30
22.41
22.35
21.04
21.00
19.68
19.00
17.00
15.00
2-Mar
3-Mar
4-Mar
5-Mar
6-Mar
7-Mar
8-Mar
9-Mar
10-Mar
11-Mar
12-Mar
Days
Weather office data
Figure 6.2:
Field study data
Profile of daily average temperature of meteorological office data and
field study data of same days in summer season.
Comparison of data during summer season indicated that minimum
temperature difference is 0.48ºC and maximum temperature difference is 2.86ºC and
average temperature difference is 7.81% in the month of March. In a city wide
observation (Karmaokar and Khatun, 1993; Hossain and Nooruddin, 1993) notable
variation in temperatures has been recorded in different parts of the city. Sharma, in
2002 found the existence of the different variations at the same locality indicates the
existence of further micro-climate variations in the same locality. During field
investigation (Sharma, 2002) also found regarding variations of the site temperature
from meteorological office data. And the maximum variation is 3.3ºC and minimum
variation 1.74ºC.
The temperature pattern indicates the influence of the urban
density over the temperature profile of the area. It is evident from the field study
that the data from the meteorological station is not universally suitable for design
purposes, as there are exists a number of variations of the local climate in Dhaka city.
Account of the physical characteristics of an urban site in predicting a maximum
temperature for the site. It is more accurate than using data from the meteorological
station at predicting extremes air temperature within a particular climate of the site.
113
6.3
Field Study
Summer field study was carried out from March to June as a base case
to evaluate the performance of upper space of the selected traditional house. These
months are selected as they represent the monsoon or hot-wet period and
characterized by high values of humidity, temperature, cloud cover and radiation.
During summer periods in the context of Dhaka, monsoon is the most prolonged
season. (For more details see chapter three). In general, the upper space thermal
environment of the test house is controlled by different percentage of window
openings during summer seasons. The intent of the study is to justify the thermal
performance of the traditional house is upper space. Therefore, closed windows of
the upper space have been considered as a base case for this research, and the
different percentage of window openings of the upper space can be compared as in
table 6.1.
Table 6.1:
The seasons and the percentage of the window opening in upper space
Season
Winter
Summer
Date
10th to 31st January
1st to 28th February
1st to 31st March
1st to 30th April
1st to 31st May
1st to 20th June
Opening of window in upper space
0%
0%
0%
25%
75%
75%
However, during the winter the openings of the upper space are totally closed
along whole season.
The field measurements were obtained for January and
February as these two months characterized the cold and dry periods.
Data was collected in three locations of the traditional houses, namely upper
space between the roof and ceiling, the indoor living space between ceiling and floor
and the outdoor data.
114
6.4
Field Study Result : Comparative study of Air Temperature of the Test
House for Justify the role of Upper Space
This section describes the indoor thermal environment of the test house with
respect to upper space. As upper space is closely related with lightweight C.I. sheet
roof and also due to its physical positioning, any temperature fluctuation on C.I.
sheet roof directly and immediately affects the upper space temperature. Therefore,
temperature fluctuation in upper space is a significant factor to be considered for this
research. A comparative study was made to judge the thermal performance of the
traditional house during summer and winter season with respect to thermal comfort
temperature range.
The performance evaluation was made on the basis of
temperature difference between indoor, outdoor and upper space (Ti= indoor
temperature; To= outdoor temperature; Tu= upper space temperature) with comfort
zone analysis (according to Mallick for winter season is 17ºC to 32ºC and for
summer is 24 ºC to 32 ºC). For thermal performance evaluation is made with daily
maximum and daily minimum air temperature is preferable for this research because
daily maximum temperature is the highest value for day time and daily minimum is
the lowest value in night time temperature value.
6.4.1. Winter Season
The Himalayan mountain range and Tibet Plateau are situated in the north of
Bangladesh. During winter season every year, one or twice Himalayan cold wind
flows over the Bangladesh from the north. Common weather conditions of Dhaka in
the winter season of 2007 for based on Bangladesh Meteorological Department data
are described in table 6.2.
115
Table 6.2:
General weather condition of Dhaka in winter season (2007)
Ave. Wind
speed
(knots) &
Direction
Month
Ave.
Temp
ºC
Humidity
%
January
18.1
68
2.9
February
21.6
68
3.1
Cloud
Condition
(octas)
Rain
Fall
mm
NW
0.6
0
NW
2.2
31
Special Weather Condition
Himalayan cold wind flow 12th
to 18th January
Common winter condition
20 January to 28 February.
Within the above (table 6.2) weather condition of winter seasons at Dhaka,
2007, the field study was done with closed windows of the upper space. Three
weather conditions are considered for this research, and are described below:
•
Analyzing air temperature during Himalayan cold wind flow
period.
•
Analyzing air temperature during Termination of Himalayan
cold wind flow period.
•
Analyzing air temperature for selected days under common
weather condition.
6.4.1.1
Analyzing air temperature during Himalayan cold wind flow period
for selected Days (12 and 13 January)
During the Himalayan cold wind flow from 12th January to 18th January,
outdoor maximum temperature was 26.73ºC and minimum temperature was 17.14ºC.
The upper space air temperature is rapidly cooled down below ambient air
temperature at night because of lots of dew formed over the outer C.I. roof in winter.
Instead of heat gain from air by condensation of dew formed, the C.I. roof surface
temperature dropped significantly below the outdoor air temperature. When upper
space gains minimum temperature at 6am the indoor temperature was still higher
than upper space and outdoor temperature (table 6.3). The relationship between
indoor temperature (Ti), outdoor temperature (To) and upper space temperature (Tu)
can be derived as Ti>Tu<To. In this situation, upper space plays a vital role to
maintaining indoor temperature higher than the outdoor and upper space temperature
116
at night of winter season. This is a desirable finding for the traditional house with
closed window in winter night.
Table 6.3:
Air temperature difference during Himalayan cold wind flow period
for selected Days (12 and 13 January)
Winter Season
Date
12
Jan.
13
Jan.
Time
when
Upper
max
1:00
PM
6:00
AM
1:00
PM
6:00
AM
Collected Data
(Air Temp.)
Indoor Upper Outdoor
( Ti)
(Tu)
(To)
ºC
ºC
ºC
Opening of window in Upper is 0%
Air Temp. Difference
Relation
(%)
Relation
Between
Remark
Between
(Tu(Tu(ToTi, Tu, &
Ti,& To
Ti)
To)
Ti)
To
/Ti
/To
/To
23.02
29.37
23.60
27.58
24.45
2.46
Day Max.
Ti<Tu>To
Ti<To
18.95
15.65
18.28
17.41
14.39
3.67
Night Min
Ti>Tu<To
Ti>To
23.08
28.24
23.28
22.36
21.31
0.86
Day Max.
Ti<Tu>To
Ti<To
19.42
16.48
18.19
15.14
9.40
6.76
Night Min
Ti>Tu<To
Ti>To
During the Himalayan cold wind flow period at day time upper space has
been reacted as vise versa of night phenomenon. The trapped air in the upper space
works as a buffer. Still air is a poor conductor. Within two hours after sunrise upper
space starts to gain heat and the upper space air temperature became higher than
indoor and outdoor temperature. From figure 6.3, the temperature graph profile of
indoor and outdoor did not gain such high temperature like the upper space
temperature.
The relationship between indoor, outdoor and upper space temperature is
derived as Ti<Tu>To. So during winter day time upper space environment condition
is more comfortable with closed windows compared to indoor space. But indoor
environment also stay within comfort temperature range at the same time. From this
phenomenon it was observed that during day time the upper space with closed
windows store some heat, and after sunset the heat starts to transmit towards indoor
space. So indoor start to gain heat from the upper space and also from indoor
features such as bulb, equipment, etc after sunset and indoor become warmer than
upper space and outdoor.
117
32.00
31.00
30.00
29.00
28.00
27.00
Temperature ºC
26.00
25.00
24.00
23.00
22.00
21.00
20.00
19.00
18.00
17.00
16.00
15.00
0
3
6
9
12
15
18
21
24
27
30
33
36
39
42
45
48
51
Selected Days of the Month Per Hour
Outdoor
Figure 6.3:
Indoor
Upper
Profile of indoor, outdoor and upper space air temperature of the test
house during Himalayan cold wind flow period (12 and 13 January)
From table 6.3 for selected two days at night the average minimum air
temperature difference between indoor and outdoor was 5.21 % of outdoor range.
During day time average maximum air temperature difference was 1.66 % of
outdoor range.
At night upper space become drastically cooler because of
conduction of outer steel roof with cold wind.
The average air temperature
difference between upper and indoor at day time was 24.97 % and at night was 16.27
% of indoor range. During day time upper space, maximum air temperature become
higher than indoor living space maximum temperature but at night upper space
minimum temperature lower than indoor minimum temperature.
The average
humidity was 59.90 % for the selected days of January month. Humidity variation is
very low during this period. Therefore, indoor living space air temperature profile is
within comfort temperature range (17ºC to 32ºC, Sharma and Ali) for day and night
in winter season during Himalayan cold wind flow period, which is a desirable
condition in traditional houses.
118
6.4.1.2
Analyzing air temperature during the Termination of Himalayan
cold wind flow period for selected Days (18 and 19 January)
When cold wind flow stopped from 18th January 8 pm then the graph profile
starts to change compared to previous condition.
On 19th January night the
minimum outdoor temperature became much lower than upper space minimum
temperature, upper space temperature profile remained in middle range between
outdoor and indoor air temperature profile. Indoor temperature is higher than the
outdoor and upper space air temperature during night time. So the relation between
indoor, outdoor and upper space temperature is Ti>Tu<To at night. During day time
the outdoor temperature is higher than upper space and indoor temperature. So the
relationship between indoor, outdoor and upper space can be shown as Ti<Tu>To at
day time.
Table 6.4:
Air temperature difference during termination of Himalayan cold
wind flow period for selected Days (18 and 19 January)
Winter Season
Date
18
Jan.
19
Jan.
Time
Upper
max
3:00
PM
7:00
AM
1:00
PM
7:00
AM
Collected Data
(Air
Temp.)
Indoor Upper Outdoor
( Ti)
(Tu)
(To)
ºC
ºC
ºC
Opening of window in Upper is 0%
Air Temp. Difference
Relation
(%)
Relation
Between
Remark
Between
(Tu(Tu(ToTi,Tu, &
Ti,& To
Ti) / To) / Ti) /
To
Ti
To
To
21.55
25.66
22.54
19.07
13.84
4.39
19.04
18.76
19.42
1.47
3.40
1.96
23.82
25.5
24.76
7.05
2.99
3.80
19.36
17.52
16.35
9.50
7.16
18.41
Day
Max.
Night
Min
Day
Max.
Night
Min
Ti<Tu>To
Ti<To
Ti>Tu<To
Ti>To
Ti<Tu>To
Ti<To
Ti>Tu>To
Ti>To
The indoor temperature was less than the upper space temperature at day
time. Outdoor and indoor temperature difference became double (10.18 %) than the
previous day 18th January (during cold wind flow period). When Himalayan cold
wind flow stopped the outdoor air temperature became maximum in day time and
minimum at night. Where as previously during Himalayan cold wind flow the upper
space air temperature was maximum in day and minimum at night (Figure 6.4).
119
In this situation, the influence upper space can help to maintain indoor
temperature higher than the outdoor temperature at night. During the day time
indoor space temperature remains lower than the outdoor temperature.
32.00
31.00
30.00
29.00
28.00
27.00
Temperature ºC
26.00
25.00
24.00
23.00
22.00
21.00
20.00
19.00
18.00
17.00
16.00
15.00
0
3
6
9
12
15
18
21
24
27
30
33
36
39
42
45
48
Selected Days of the Month, Per hour
Outdoor
Figure 6.4:
Indoor
Upper
Profile of indoor, outdoor and upper space air temperature of the test
house during termination of Himalayan cold wind flow period (18
and 19 January)
From table 6.4 for selected two days at night the average minimum air
temperature difference between indoor and outdoor was 10.18 % compared to
outdoor range. During day time average maximum air temperature difference was
4.09 % of outdoor range. At night, the upper space becomes cool immediately after
sunset because of conduction of outer C.I sheet roof with cold wind flow. The
average air temperature difference between upper and indoor at day time was 13.06
% and at night was 5.84 % of indoor range.
During day time, the upper space air temperature is hotter than indoor air
temperature but at night it is cooler than indoor living space. The general
120
relationship between outdoor temperature and relative humidity is that when one
reach its peak temperature than other goes down. The humidity was 46.79 % for the
selected days of January month. Humidity variation is noticeable in this period.
Therefore, indoor temperature profile is also within comfort temperature range for
day and night in winter season after termination of Himalayan cold wind flow.
6.4.1.3
Analyzing air temperature for selected days under common weather
condition during winter season (20and 21 January, 10 February and 27
and 28 February)
The rest of the winter period remains under common weather condition
which is shown in table 6.2. From the month of January and February, five days
were selected (see 1.7 in chapter 1) in order to understand the general performance
of the traditional house during winter season at dense Dhaka city in Bangladesh.
Table 6.5:
Air temperature difference under common condition during rest of
winter period for selected days of January and February.
Winter Season
Date
20
Jan.
21
Jan.
10
Feb.
27
Feb.
28
Feb.
Time
Upper
max
3:00
PM
6:00
AM
3:00
PM
6:00
AM
3:00
PM
6:00
AM
4:00
PM
7:00
AM
3:00
PM
6:00
AM
Collected Data
(Air Temp.)
Indoor Upper Outdoor
(Ti)
(Tu)
(To)
ºC
ºC
ºC
Opening of window in Upper is 0%
Air Temp. Difference
Relation
(%)
Relation
Between
Between
Remark
(Tu(Tu(ToTi, Tu, &
Ti,& To
Ti)/
To)/
Ti)/
To
Ti
To
To
24.43
25.56
25.37
4.63
0.75
3.71
19.49
17.84
16.00
8.47
11.50
21.81
25.17
26.34
26.90
4.65
2.08
6.43
19.45
18.28
17.90
6.02
2.12
8.66
26.80
29.00
30.04
8.21
3.46
10.79
22.86
21.33
19.52
6.69
9.27
17.11
28.73
29.70
29.80
3.38
0.34
3.59
24.30
22.48
18.41
7.49
22.11
31.99
29.14
29.63
30.11
1.68
1.59
3.22
24.79
22.99
22.00
7.26
4.50
12.68
Day
Max.
Night
Min
Day
Max.
Night
Min
Day
Max.
Night
Min
Day
Max.
Night
Min
Day
max.
Night
Min
Ti<Tu>To
Ti<To
Ti>Tu>To
Ti>To
Ti<Tu<To
Ti<To
Ti>Tu>To
Ti>To
Ti<Tu<To
Ti<To
Ti>Tu>To
Ti>To
Ti<Tu<To
Ti<To
Ti>Tu>To
Ti>To
Ti<Tu<To
Ti<To
Ti>Tu>To
Ti>To
121
32.00
31.00
30.00
29.00
28.00
27.00
Temperature ºC
26.00
25.00
24.00
23.00
22.00
21.00
20.00
19.00
18.00
17.00
16.00
15.00
0
7
14
21
28
20 and 21 January
35
42
49
56
63
70
10 February
Per Hour
outdoor
Figure 6.5:
77
Indoor
84
91
98 105 112 119
27 and 28 February
126
133
140
Upper
Profile of indoor, outdoor and upper air temperature in common
weather condition of the test room without window opening in the
upper during winter season for selected days
From figure 6.5 the temperature profile during day time represents the per
hour air temperature that indicates an increase from the January 3rd week to February
last week and this tendency of increase of air temperature was observed as the
season progress.
Common condition for winter seasons at night is reflected by the outdoor
temperature becoming cooler than upper space temperature. For both day and night
the upper space temperature graph profile remained in the middle range between the
outdoor and indoor air temperature graph profile. Indoor temperature is higher than
the outdoor and upper space air temperature during night time. So at night time
when people stay in their houses, the indoor environment is warmer than outdoors
which is desirable during winter seasons.
During the day time, the outdoor
temperature is higher than the upper space and indoor temperature. But indoor
living space and upper space air temperature still remains within comfort range 17ºC
to 32ºC (Sharma and Ali).
122
It was summarized from table 6.5, for the selected five days at night the
average minimum air temperature difference between indoor and outdoor was
18.45% compared to outdoor range.
During day time average maximum air
temperature difference was 5.54% of outdoor range. At night the upper space
became cooler because of conduction of outer C.I sheet roof with cold wind flow.
The average air temperature difference between upper space and indoor at day time
was 3.71 % and at night was 4.28 % of indoor range.
As a conclusion of the field study in winter season, according to outdoor data
analysis the minimum outdoor air temperature is recorded at 15ºC which is below
2ºC of lower limit of the comfort temperature range (17ºC to 32ºC). The average
humidity was 62.82% for the selected days of January and February months. Along
with other previous research (Hossain & Nooruddin, 1993), this research also
indicates that winter season in Bangladesh is comfortable.
This research also
concludes that with closed windows, the upper space temperature is remaining
cooler than the outdoor temperature at day time and it becomes higher at night time.
For this reason the indoor temperature remains in the comfort temperature range
(17ºC to 32ºC). For better thermal environment in indoor living space during winter
periods it is recommended that window openings, of upper space need to be closed
throughout the winter seasons. So the Bangladesh traditional house has an ability to
create a indoor comfortable environment during winter seasons.
6.4.2. Summer Season
The pre-monsoon period covers the months of March, April and May and it
is characterized by occasional thunderstorms, and an average maximum temperature
of 34°C. The mean maximum temperatures reported in April with a decreasing
tendency up to August. The mean temperature increases from January to April, then
remains almost constant up to September, and decreases towards January (Hossain &
Nooruddin, 1993). The mean minimum temperature is lowest in January, increases
up to June and remains fairly constant up to September and decreases after that
(Karmokar et al, 1993). According to Karmokar’s and Hossain & Nooruddin’s study,
123
it was decided that the research field study be considered for summer season from
March to June. Within these months the common weather condition remains almost
same for the whole period. The field study was obtained in the summer season with
different percentage of window opening of the upper space to justify the indoor
living space air temperature of the traditional house within the worst condition at
dense Dhaka city in Bangladesh.
Table 6.6:
Month
Common weather condition of Dhaka in summer according to BMD
Ave.
Temp
ºC
Humidity
%
Ave. Wind
speed
(knots) &
Direction
Cloud
Condition
(octas)
Rain Fall
mm
March
25.4
54
4.2
NW
1.4
11
April
28.3
69
3.8
S
4.3
163
May
30.1
70
3.5
S
4.3
185
June
28.7
81
3.1
S
6.3
753
6.4.2.1
Special Condition
Common weather
condition
hot and Dry
Hot and wet
Field study result of 7th March and 8th March without any opening in
upper space during summer season
Indoor air temperature depends on certain external factors, where upper space
can play an important role. The significant findings of temperature data recorded
from field study for the indoor during selected day of March without window
opening of upper space are described below.
124
Table 6.7:
Air temperature difference, under common condition during summer
for selected days without window opening in the upper space
Summer Season
Date
Time
Upper
max
3:00
PM
7:00
AM
3:00
PM
8:00
AM
7
Mar.
8
Mar.
Collected Data
( Air Temp.)
Indoor Upper
Outdoor
( Ti)
(Tu)
(To)
ºC
ºC
ºC
Opening of window in Upper is 0%
Air Temp. Difference
Relation
(%)
Relation
Between
Remark
Between
(Tu(Tu(ToTi,Tu, &
Ti,& To
Ti) /
To)
Ti) /
To
Ti
/ To
To
27.29
30.71
30.91
12.53
0.65
11.71
23.47
21.30
20.25
9.25
5.19
15.90
27.65
30.74
30.88
11.18
0.45
10.46
22.92
20.73
19.49
9.55
6.36
17.60
Day
Max.
Night
Min
Day
Max.
Night
Min
Ti<Tu<To
Ti<To
Ti>Tu>To
Ti>To
Ti<Tu<To
Ti<To
Ti>Tu>To
Ti>To
32.00
31.00
30.00
29.00
28.00
27.00
Tempearture ºC.
26.00
25.00
24.00
23.00
22.00
21.00
20.00
19.00
18.00
17.00
16.00
15.00
0
3
6
9
12
15
18
21
24
27
30
33
36
39
42
45
48
Per hour
Outdoor
Figure 6.6:
Indoor
Upper
Profile of indoor, outdoor and upper air temperature of the indoor
living without window opening in the upper space in selected days in
month of March (7 and 8 March)
From figure 6.6 the temperature profile of indoor, outdoor and upper space
indicates that the upper space air temperature was little bit higher than the outdoor
temperature at day and night time. From figure 6.6 the upper is 3ºC higher than the
indoor but almost same with the outdoor air temperature during day time. So 0%
125
opening in upper space trapped cold air works as a buffer to transmit the heat from
outdoor to indoor living space through the upper space at day time. Assumption
about traditional house without upper space, the indoor living space temperature will
be higher than the outdoor temperature. However, due to the closed windows of the
upper space the indoor temperatures remain cooler than the outdoor temperature at
day time. At night, the upper space temperature is lesser by 2ºC from the indoor
temperature and 1ºC from outdoor. It affects the indoor temperature by keeping it
warmer than the outdoor temperature. This temperature difference contributes to
elevate the ambient air temperature of the indoor living space and causes an
uncomfortable thermal environment. During summer season with 0 % window
openings of upper space during day time shows effectiveness in maintaining the
thermal comfort environment of the indoor environment. But at night, it creates
undesirable conditions in the indoor living space. Due to the hot trapped air in upper
space, heat is transmitted into the indoor space. Therefore, there is no potential of
cooling immediately at night time. The average indoor humidity was 42.36 % for
the selected days on March. March is the month of the end of cold and dry winter
seasons and the start of hot and dry summer seasons. During day time with closed
windows, the upper space helps to maintain the indoor temperature within
comfortable temperature range (24ºC to 32ºC). The relationship between indoor,
outdoor and upper space at night is Ti<Tu>To. So the upper space with closed
windows is playing a vital role to keep the indoor temperature within the comfort
temperature range only during day time in summer season.
For selected two days at night the average minimum air temperature
difference between indoor and outdoor was 16.75 % of outdoor range. During day
time, the average maximum air temperature difference was 11.08 % of the outdoor
range. The average air temperature difference between upper and indoor at day time
was 11.85 % and at night was 9.40 % of indoor range. At night with 0% percent
opening the upper space becomes cooler because of conduction of outer C.I sheet
roof but higher than outdoor temperature. The relationship between indoor, outdoor
and upper space at night is Ti>Tu>To. During night time with closed windows, the
upper space influences the indoor living space temperature by becoming warmer
than the outdoor temperature.
126
Field study results from 1st April to 2nd April with 25% (percent)
6.4.2.2
window openings in upper space
The significant findings of temperature data recorded from the field study for
the indoor living space during selected day of April with 25% window opening in
upper space are described below.
Table 6.8:
Air temperature difference under common condition during summer
periods for selected days with 25 % window opening in the upper space
Summer Season
Date
1st
Apr.
2nd
Apr.
Time
Upper
max
12:00
PM
6:00
AM
2:00
PM
6:00
AM
Collected Data
(Air Temp.)
Indoor Upper Outdoor
(Ti)
(Tu)
(To)
ºC
ºC
ºC
Opening of window in Upper is 25%
Air Temp.
Relation
Difference (%)
Relation
Between
Between
(Tu- (Tu- (To- Remark
Ti, Tu, &
Ti,& To
Ti)/
To)/ Ti)/
To
Ti
To
To
32.04
37.63
34.68
17.45
8.51
7.61
28.70
26.05
26.67
9.23
2.32
7.61
33.70
37.50
35.31
11.28
6.20
4.56
28.87
26.63
26.96
7.76
1.22
7.08
Day
Max.
Night
Min
Day
Max.
Night
Min
Ti<Tu>To
Ti<To
Ti>Tu<To
Ti>To
Ti<Tu>To
Ti<To
Ti>Tu<To
Ti>To
From figure 6.7 the upper space temperature profile is rapidly increased at
noon (37.63 ºC highest). And from 2pm the temperature starts to reduce rapidly.
After 5 pm the temperature profile of the upper space remains lower than indoor
living space temperature profile. At 9 pm the outdoor and upper space temperature
were recorded to be same and after 11pm the upper space temperature starts to
decrease and remain below outdoor temperature profile. Both the magnitude and
fluctuation of upper space temperature are higher than indoor temperature.
Temperature ºC.
127
40.00
39.00
38.00
37.00
36.00
35.00
34.00
33.00
32.00
31.00
30.00
29.00
28.00
27.00
26.00
25.00
24.00
23.00
22.00
21.00
20.00
0
3
6
9
12
1 April
15
18
21
24
27
30
33
36
39
2 April
42
45
48
Per hour
outdoor
Figure 6.7:
Indoor
Upper
Profile of indoor, outdoor and upper air temperature of the indoor
living space with window opening in the upper space in summer
season (1st and 2nd April)
With 25% window openings the upper space temperature is increased by
convection and radiation process during day time and at night allows long wave
radiation for cooling.
Therefore, window openings of the upper space are a
significant factor to be considered in this research. The upper space temperature was
higher than the outdoor temperature at day time. The convectional heat gain by
window and direct solar radiation heat gain by C.I sheet roof have influence the
increase of the temperature of the upper space. Indoor space temperature reached its
peak after three hours later than upper space maximum temperature. The upper
space is transmitting heat into indoor space during day time which creates an
uncomfortable indoor environment.
From 9am to 3pm the upper space air
temperature is rising and it remains higher than the outdoor temperature.
average humidity of indoor was 56.56 % for the selected days of April month.
The
128
For the selected two days, the average minimum air temperature difference
between indoor and outdoor was 7.34 % of outdoor range. During day and night
time average maximum air temperature difference was 6.08 % of the outdoor range.
The average air temperature difference between upper and indoor at day time was
14.36 % and at night was 8.49 % of indoor range. At night, the upper space
temperature decreased immediately after sunset.
The significant findings, during 25% window openings in upper space, are
suggested that, the upper space influence the increasing of the indoor temperature
during day time. But it is helpful for night cooling process, by long wave radiation
and convectional heat loss of upper space. This plays a vital role to keep the indoor
living space temperature within comfort temperature range (24ºC to 34ºC) during
night.
6.4.2.3
Field study result of 7th and 8th May, 14th and 15th June and 19th and
20th June with, 75% (percent) opening in upper space in summer
season
The significant findings of air temperature data recorded from the field study
for the test house during selected days of May and June with 75% (percent) window
openings of upper space are described in table 6.9.
129
Table 6.9:
Air temperature difference under common condition during summer
periods for selected days with 75 % window opening in the upper
space
Summer Season
Date
7
May.
8
May.
14
Jun.
15
Jun.
19
Jun.
20
Jun.
Time
Upper
max
3:00
PM
4:00
AM
3:00
PM
6:00
AM
1:00
PM
4:00
AM
3:00
PM
5:00
AM
4:00
PM
6:00
AM
12:00
PM
5:00
AM
Opening of window in Upper is 75%
Collected Data
(Air Temp.)
Air Temp. Difference
(%)
Indoor
( Ti)
ºC
Upper
(Tu)
ºC
Outdoor
(To)
ºC
(TuTi)/
Ti
(TuTo)/
To
(ToTi)/
To
35.70
37.88
36.57
6.11
3.58
2.38
29.10
26.34
27.52
9.48
4.29
5.74
34.85
37.44
35.27
7.43
6.15
1.19
28.70
26.73
27.12
6.86
1.44
5.83
32.59
37.48
33.87
15.00
10.66
3.78
27.52
27.52
27.52
0.00
0.00
0.00
33.35
35.55
34.90
6.60
1.86
4.44
28.70
27.52
27.85
4.11
1.18
3.05
33.98
38.36
36.47
12.89
5.18
6.83
29.50
29.03
28.67
1.59
1.26
2.90
33.24
37.88
35.24
13.96
7.49
5.68
29.60
28.54
28.41
3.58
0.46
4.19
Remark
Day
Max.
Night
Min
Day
Max.
Night
Min
Day
Max.
Night
Min
Day
Max.
Night
Min
Day
Max.
Night
Min
Day
Max.
Night
Min
Relation
Between
Ti, Tu, &
To
Relation
Between
Ti,& To
Ti<Tu>To
Ti>To
Ti>Tu<To
Ti<To
Ti<Tu>To
Ti>To
Ti>Tu<To
Ti>To
Ti<Tu>To
Ti<To
Ti=Tu=To
Ti=To
Ti<Tu>To
Ti<To
Ti>Tu<To
Ti>To
Ti<Tu>To
Ti<To
Ti>Tu>To
Ti>To
Ti<Tu>To
Ti<To
Ti>Tu>To
Ti>To
During the selected six days, the average minimum air temperature difference
between indoor and outdoor was 1.82 % of outdoor range at night. During day time
the average maximum air temperature difference between indoor and outdoor was
3.75 % of outdoor range. Upper space becomes cooler after the sunset. The average
air temperature difference between upper and indoor at day time was 9.22 % and at
night was 2.01 % of indoor range.
The general relationship between outdoor
temperature and relative humidity is that when one reaches its peak, the relative
humidity drops to its minimum and vise versa. The humidity range was 78.93 % for
the selected days of May and June.
130
40.00
39.00
38.00
37.00
36.00
35.00
Temperature ºC
34.00
33.00
32.00
31.00
30.00
29.00
28.00
27.00
26.00
25.00
24.00
0
7
14
21
28
35
7 and 8 may
42
49
Outdoor
Figure6.8:
56
63
70
77
84
14 and 15 june
Per Hour
91
98
105
Indoor
112 119 126
19 and 20 June
133
140
147
Upper
Profile of indoor, outdoor and upper air temperature of the test room
with 75% window opening in the upper space
When the window openings of the upper space is 75% during day time, then
upper space upper space temperature profile becomes higher than the outdoor
temperature, at the same time indoor temperature profile remains lower than the
outdoor temperature because upper space gains heat by convection and direct solar
radiation. During night time the upper space temperature and outdoor temperature
almost same but indoor temperature become higher than outdoor and upper space
because after sunset the heat transfer from upper space to indoor that effect the
indoor temperature to increase.
So the indoor air temperature profile exceeds the comfort range temperature
during day time (24ºC to 32ºC in still air condition). During 10am to 5pm (only 7 to
8 hours within 24 hours) the air temperature remains over 32ºC which is not
desirable for indoor thermal comfort environment. The high temperature of the
upper space is reduced slowly by emission of long wave radiation and consequently
by convective heat loss from 3pm in the afternoon. At 5pm the equilibrium is
established between heat gain and loss where the upper space, indoor and outdoor
remains at the same temperature. After 6pm the indoor space temperature starts to
131
decrease and remains within comfortable range.
This phenomenon creates a
desirable condition of the indoor living space in summer night
6.5
Performance Evaluation of Daily Maximum and Minimum Temperature
with respect to Thermal Comfort Temperature Range
The respective findings of the maximum and minimum air temperature data
recorded from the field investigation for the test room in summer and winter
season’s performance respect to comfort range temperature, are described below:
6.5.1
Evaluate Maximum and Minimum Air Temperature in Winter Season
In a wide range of climatic conditions for winter after Givoni (Figure 4.2),
Sharma and Ali suggested the temperature range is from 17 ºC to 32 ºC while
humidity range is fixed between lower limit 25% to upper limit 80% (Mallick, 1994;
Abu Mukim Mridha, 2002).
A comparative study is made to evaluate the thermal performance of upper
space with respect to maximum and minimum air temperature, and to understand its
impact on the indoor environment of the test house.
During the winter season the maximum and minimum indoor air temperature
was 30.78°C in February and 17.14°C in January was recorded during the period of
field data collection in the months of January and February which is within the
comfort range without any openings in the upper space. Outdoor maximum and
minimum temperature are also within the comfort range.
Upper space air
temperature maximum and minimum was recorded at 31.93°C and 14.09°C in
January because of the Himalayan cold wind flow.
132
The temperature difference between outdoor and indoor maximum clearly
indicates that outdoor is higher than indoor when the window opening of the upper
space is totally closed. During the period of Himalayan cold wind flow (12th to
18th of January) the magnitude of upper space temperature reaches over 31°C.
34.00
31.00
28.00
Temperature °C
25.00
22.00
19.00
16.00
13.00
10.00
0
3
6
9
10th to 27th January
12
15
18
21
9,10 27 and 28 February
24
Per Days
Outdoor Max
Indoor Max
Upper Max
Outdoor Min.
Indoor Min
Upper Min
Within the comfort temperature (17°C to 32°C)
Figure 6.9:
Profile of maximum and minimum air temperature of indoor, outdoor
and upper space from field study during winter season without
opening in the upper space (10-27 January and 9, 10, 27 & 28
February, 2007)
Not only the magnitude of outdoor and upper space maximum temperature is
higher than indoor temperature but also the temperature difference between upper
and indoor air temperature is high 4ºC to 8 ºC (Figure 6.9). On the other hand, when
the wind flow stopped, the temperature remains lower compared to previous
temperature in upper space. It is evident that indoor temperature fluctuation with
outdoor and upper space is low at day time and high at night. This phenomenon
justifies the fact that the introduction of 0 % window opening during winter season
133
in upper space not only increase indoor maximum air temperature to a comfortable
level but also obstructs the main passage of heat loss from the indoor environment at
night.
6.5.2
Evaluate Maximum and Minimum Temperature in Summer Season
In summer season the lower and upper limit of comfort temperature is 24 ºC
and 32 ºC (Mallick, 1994) while the humidity ranges, between 50% and 95%, in a
condition with no air movement. The range of comfort temperature is increased
(higher limit) with the introduction of airflow, and people feel comfortable above 34
ºC with air flow at the rate of 0.30 m/s. Tolerance temperature can further be
increased to 36 ºC with air flow at the rate of 0.45 m/s (Mallick, 1994).
A
comparative study is made to evaluate the thermal performance of upper space with
respect to maximum and minimum air temperature, and to understand its impact on
the indoor environment of the test house.
45.00
42.00
39.00
Temperature °C
36.00
33.00
30.00
27.00
24.00
21.00
18.00
15.00
0
7
14
21
0% window opening
28
35
42
49
25 % Window Opening
56
63
70
77
84
75 % window opening
91
98
105
Per Days
Outdoor Max
Indoor Max
Upper Max
Outdoor Min
Indoor Min
Upper Min
Within the comfort temperature (24ºC to 32 ºC)
Figure 6.10: Profile of maximum and minimum temperature of indoor, outdoor
and upper air temperature of the test house
134
During day time the upper space maximum temperature is rising with
increasing the percentage of window opening of upper space, because of
convectional heat gain from ambient air and direct solar radiation. Due to the dense
surroundings cross ventilation in upper and indoor living space is negligible.
Table 6.10:
Tabular format of indoor temperature within comfort range for
summer season
Season
Month
March
April
Summer
May
June
Window
opening of
upper space
0 % percent
25 % percent
75 % percent
75 % percent
Indoor temperature within comfort range
(%)
Day Max.
Night Min. Temp.
Temp
70
100
20
100
17.24
100
34
100
From analyzing table 6.10, it is visible that when window openings were
25%, the indoor maximum temperature becomes low. On the other hand, with
75% window openings during day time, the indoor maximum temperature
becomes lower during the same characterized period April and May which is hot
and dry. In the month of June which is characterized as hot and wet period, with
75% window openings, the percentage of indoor maximum temperature in respect
of comfort temperature becomes higher because of rainfall, which is negligible in
March. It is justified that during the summer season, the window openings of
upper space will become effective when it remain totally closed in the day time
and open at night time for better performance of thermal environment in indoor.
Outdoor and upper space maximum temperature is higher than indoor
maximum temperature and the temperature difference between indoor and outdoor is
greater (Figure 6.10) during summer season at day time when there is no window
openings in the upper space. Furthermore, when the window openings of the upper
space is 25% and 75%, then the upper space and outdoor temperature become almost
similar at night time and the temperature difference between indoor and outdoor
becomes low. It is evident that indoor temperature fluctuation with outdoor and
upper space is highest at day time and at night it remains lowest which is regulated
by opening the windows. This phenomenon justifies the fact that the opening the
135
windows during summer seasons of the upper space not only increase the indoor
maximum air temperature to a uncomfortable level but at night allows the main
passage of heat loss from the indoor living space to create a comfortable living
environment.
6.6
Comparative Study of Temperature difference between Indoor
maximum, Outdoor maximum and Upper maximum for selected days
7.00
6.50
6.30
6.00
0 % window opening
5.50
5.00
0 % window
opening
25 % window
opening
75 % window
opening
4.76
4.75
Tem perature ºC
4.50
3.92
4.00
3.61
3.50
3.50
3.22
3.00
2.80
2.59
2.50
1.98
2.00
1.75
1.55
1.50
1.33
1.24
1.31
1.26
0.81
1.00
0.44
0.50
0.00
19/1
10/2
1/4
7/5
14/6
Summer Season
Winter Season
Selected Day of the Months
Indoor-Outdoor
Figure6.11:
7/3
Outdoor-Upper
Indoor-Upper
Profile of maximum temperature difference of indoor, outdoor and
upper space air temperature of the test house in the selected days
Temperature difference between daily indoor maximum and outdoor
maximum is another indicator by which thermal performance of upper space can be
judged are as figure 6.11, clearly illustrates that cooling potential is pronounced with
increasing the percentage of openings of upper space.
136
In winter seasons, when the Himalayan cold wind flow occurs, the indoor
and outdoor temperature difference was high and when the cold wind flow ceased,
then the indoor and outdoor temperature difference become less. This phenomenon
is positive for comfortable indoor thermal environment.
In March, when the opening of upper space was 0%, the temperature
difference between outdoor and indoor maximum temperature is higher than the
whole summer season. Chronologically, this difference of temperature fluctuates
downward with the increase of the percentage of the window opening of upper space.
The temperature difference between indoor and upper space is becoming higher
comparatively with the temperature difference of indoor and outdoor when the
window openings were 25 % to 75%. Upper space with window openings works as
a heat storage at day time and influences the indoor temperature to rise.
By
increasing the percentage of window opening of upper space, the outdoor and indoor
maximum temperature difference becomes low whereas the indoor and upper space
maximum temperature difference becomes higher. These phenomena justifies the
fact that the upper space works as a buffer to obstruct the main passage of heat gain
of indoor environment when the window openings was closed at day time during
both seasons. With the increased of the percentage of window openings of upper
space in summer seasons, it improves the indoor comfort environment at night time.
6.7
Comparative study of Winter and Summer Season at 6.00 am and 6.00
pm
Comparative study between sunrise and sunset time according to BST 6.00
AM and 6.00 PM with humidity justifies the performances of traditional house at
day and night time during winter and summer seasons.
137
6.7.1
Winter Season with Closed Window in Upper Space
The winter sun rise and sunset is 5.30am and 5.30pm. After sunrise from
6.00am the temperature profile starts to increase and attains maximum value at
2.00pm to 3.00pm (BST). After sunset from 6.00pm the temperature starts to change.
Therefore comparing the temperature difference between day and night at 6.00 am
and 6.00 pm is important.
The general relationship between indoor air temperature and indoor relative
humidity is that inversely related each other. Relative humidity decrease at daytime
and increase night. The indoor minimum value of relative humidity is at 6.00 pm
when the indoor space remains maximum temperature. So relative humidity is
inversely related with temperature figure 6.12.
65.00
40.00
60.00
35.00
30.00
50.00
45.00
25.00
Temperature ºC
Relative Humidity %
55.00
40.00
20.00
35.00
15.00
0
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
30.00
6.00 AM
6.00 PM
RH
Per Hour
Indoor
6.00 AM
Outdoor
6.00 PM
Upper
Figure 6.12: Profile of temperature of indoor, outdoor and upper space air
temperature of the test house at 27th and 28th February, 2007
138
Table 6.11:
Date
27.
Feb
28.
Feb
Selected days temperature difference between 6am to 6pm
Time
6.00AM to 6.00PM (Day)
6.00PM to 6.00AM (Night)
6.00AM to 6.00PM (Day)
Temperature Difference
Indoor Upper Outdoor
3.94
6.33
10.01
3.62
5.72
6.39
3.75
5.49
Relation of
temperature change
6.69
Ti<Tu<To
Ti<Tu<To
Ti<Tu<To
The temperature of outdoor becomes two and half (10.01/3.94=2.55) times
more than indoor within 12 hours in the day time and at night becomes one and three
quarter (6.39/3.62=1.76) times more than indoor space. Upper space temperature is
one and three quarter (6.33/3.94=1.6) times more than indoor space at day time and
one and half (5.72/3.62=1.58) times more at night.
During the winter season, comfort temperature range is 17 ºC to 32 ºC while
relative humidity range is fixed in 25% (lower limit) to 80% (upper limit). After
sunrise (6 am to 6 pm), the temperature changes from 6.69ºC to 10.01ºC at the
outdoor and within this time, the indoor space temperature changed from only
3.75ºC to 3.94ºC (table 6.11). So during day time when outdoor temperature change
rapidly the indoor space temperature did not change as the outdoor, because the
upper space temperature profile always remains the middle range of the outdoor and
indoor space temperature profile.
For day and night time the relationship of
temperature difference between indoor, outdoor and upper space is Ti<Tu<To. So
the upper space with closed window is working as buffer during winter season.
6.7.2
Summer Season, with 0% Window Opening of Upper Space
During summer months, when outdoor temperature starts to increase, the
indoor and upper space air temperature also increases as high as the outdoor
temperature condition when there is no opening at the upper space.
139
55.00
33.00
50.00
31.00
29.00
45.00
25.00
35.00
23.00
Temperature ºC
Relative Humidity %
27.00
40.00
30.00
21.00
25.00
19.00
17.00
15.00
15.00
0
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
20.00
6.00 AM
Per Hour
6.00 PM
RH
Indoor
6.00 PM
6.00 AM
Outdoor
Upper
Figure 6.13: Profile of temperature of indoor, outdoor and upper air temperature of
the test house at 7th and 8th March, 2007
Table 6.12:
Date
7 Mar
8 Mar
Selected days temperature difference at 6am and 6pm
Time
6.00AM to 6.00PM
6.00PM to 6.00AM
6.00AM to 6.00PM
Temperature Difference
Indoor
Upper
Outdoor
3.62
7.04
7.47
4.04
7.74
8.17
4.04
8.31
7.93
Relation of
temperature change
Ti<Tu<To
Ti<Tu<To
Ti<Tu>To
The temperature of outdoor becomes two (7.47/3.62=2.06) times more than
indoor space within 12 hours in the day time and at night also double (8.17/4.04=2.0)
than indoor space.
Upper space temperature is almost twice as much
(7.04/3.62=1.94) than indoors at day and night times. For day time it is beneficial
but for night it is difficult to lose heat from indoor space because the trapped hot air
temperature at upper space starts to be transmitted into the indoor space. Therefore,
indoor and outdoor temperature difference becomes consistently higher at night,
which is undesirable for summer nights.
During summer season, the comfort temperature range is between 24 ºC to 32
ºC while relative humidity range is fixed in 50% (lower limit) to 90% (upper limit).
Indoor temperature conditions after sunrise (6.00am to 6.00pm), 9 hours (10am to
6pm) indoor temperature is lower than outdoor temperature and after sunset (6pm to
140
6am), 12 hours indoor living space is hotter than outdoor ambient environment in
summer season. So the upper space with closed windows during summer season at
day time is desirable but for night it is not for indoor comfort in the traditional house
in Bangladesh.
6.7.3
Summer Season with 75% Window Opening in Upper Space
During summer when outdoor temperature starts to increase, indoor air
temperature also increases as high as the outdoor temperature condition and upper
space air temperature become higher than outdoor temperature during day time after
sun rise. But after sunset the upper space and outdoor temperature profile become
almost the same and they remain lower than indoor space temperature profile.
Indoor relative humidity decreases at daytime and increases at night. The
minimum value of Rh is around 3.00pm, when the temperature of the day reached its
peak and Rh is inversely related with temperature.
40.00
90.00
85.00
35.00
75.00
30.00
70.00
25.00
65.00
Temperature ºC
Relative Humidity %
80.00
60.00
20.00
55.00
15.00
0
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
50.00
6.00AM
6.00PM
RH
Per Hour
Indoor
6.00AM
Outdoor
6.00PM
Upper
Figure 6.14: Profile of temperature of indoor, outdoor and upper air temperature of
the test house at 19th and 20th June, 2007
141
Table 6.13:
Date
Selected days temperature difference at 6am and 6pm
Time
19.
Jun
6.00AM to 6.00PM (Day)
6.00PM to 6.00AM (Night)
20.
Jun
6.00AM to 6.00PM (Day)
Temperature Difference
Indoor Upper Outdoor
2.74
3.18
2.31
2.94
3.67
2.57
2.71
3.87
3.11
Relation of
temperature change
Ti<Tu>To
Ti<Tu>To
Ti<Tu>To
The temperature variation in outdoor becomes more than three quarter
(2.31/2.74=0.85) times than indoor space within 12 hours in the day and night.
Upper space temperature variation is one and quarter (3.18/2.74=1.16) times more
than indoor space at day time and more than one and quarter (3.67/2.94=1.24) times
more at night. During day time the indoor and outdoor temperature variations are
almost the same which is undesirable for indoor comfort environment. But at night
the indoor and outdoor temperature variation is at its minimum which is suitable for
thermal comfort environment of indoor living spaces. The upper space with 75%
window openings influences the upper spaces through quick heat loss by convection
and long wave radiation. During day time, the upper space gains heat by convection
and direct solar radiation. Within 24 hours, only 7 hours during day time from 10am
to 5pm the indoor temperature of traditional house exceeds the comfort temperature
range. Before sunset around 4pm the indoor and upper space temperature falls
below the outdoor temperature as the long wave radiation began to exceed the
convective gain.
Duration time and hour of indoor thermal comfort temperature range (24ºC to
32ºC in summer, 17ºC to 32ºC in winter) of the traditional house in Bangladesh, for
the selected days according to different percentage of window openings in the upper
space are describe in table 6.14.
142
Table 6.14:
Tabular format of duration time and hour of indoor space thermal
comfort environment
Season
Winter
Summer
Month
Date
January
February
March
12 Jan.
10 Feb.
7 Mar.
April
1 Apr.
May
7 May.
June
14 Jun.
Uncomfortable
Time & hours
none
none
none
12pm to 8pm
(8 hours)
10am to 6pm
(8 hours)
12pm to 5pm
(6 hours)
Window
opening of upper
space
Comfortable
hours within
24 hours
Comfortable
hours
%
0 % percent
0 % percent
0 % percent
24
24
24
100
100
100
25 % percent
16
66
75 % percent
16
66
75 % percent
18
75
From the table 6.14 information, it can be summarized that the traditional
house in Bangladesh has a better ability to provide thermal comfort in indoor
environment during night time for both summer and winter seasons. During summer
day time if the window opening of upper space increases, then indoor space become
uncomfortable for 7-8 hours starting from 10am to 6pm when maximum activity
done in outside of the house. But after sunset the indoor environment temperature
drops within comfort temperature range. At the night time when people stay at home
for longer periods, the indoor space temperature remains within comfortable range,
which is desirable.
6.8
Study of Comfort Zone Analysis of Winter and Summer Seasons
Comfort zone (further details in chapter Four) is outlined on the basis of
indoor air temperature, indoor relative humidity and air flow, particularly devised for
summer comfort. In still air situation, the boundary conditions for air temperature are
between 24-32 ºC and upper limit is increased to slightly over 34 ºC with 0.3 m/s air
speed and nearly 36 ºC with 0.45 m/s air speed (Mallick, 1993). For winter after
Givoni (Figure 4.2), Sharma and Ali (1986) suggested the temperature range is from
17 ºC to 32 ºC while humidity range is fixed in lower limit 25% to upper limit 80%
(Mallick, 1994; Abu Mukim Mridha, 2002).
143
Temperature ºC
6.8.1
Evaluation of Indoor Comfort During Summer Seasons
40.00
39.00
38.00
37.00
36.00
35.00
34.00
33.00
32.00
31.00
30.00
29.00
28.00
27.00
26.00
25.00
24.00
23.00
22.00
21.00
20.00
19.00
18.00
17.00
16.00
15.00
14.00
air movement
0.45 m/s
0.30 m/s
30
40
50
60
70
80
90
100
Relative Humidity (%)
Figure 6.15: Plotting of the indoor temperature and the indoor relative humidity of
the indoor living space within summer comfort zone.
Relationship between daily average indoor relative humidity and daily
average indoor temperature of the indoor space with superimposing summer comfort
zone on the figure 6.15, certain thermal comfort information can be traced out.
Scatter diagrams show some points almost 9% are outside of the comfort zone in still
air situation according to temperature and almost 91% are inside the comfort
temperature range. Whereas the concentrated majority of points are between 40% 85% relative humidity and temperature 25ºC-34ºC. From the figure 6.16, it is
indicated that March month is dry and May is the hottest month according to this
research. However, with the increase of air flow 0.3m/s, the comfortable condition
of indoor living thermal environment can be achieved successfully in the traditional
house in Bangladesh in the context of Dhaka city. Evaluation of the diagram for the
comfort zone analysis for the test house in different months is discussed below,
144
April month
Temperature ºC
Temperature ºC
March month
40.00
39.00
38.00
37.00
36.00
35.00
34.00
33.00
32.00
31.00
30.00
29.00
28.00
27.00
26.00
25.00
24.00
23.00
22.00
21.00
20.00
19.00
18.00
17.00
16.00
15.00
14.00
30
40
50
60
70
80
90
40.00
39.00
38.00
37.00
36.00
35.00
34.00
33.00
32.00
31.00
30.00
29.00
28.00
27.00
26.00
25.00
24.00
23.00
22.00
21.00
20.00
19.00
18.00
17.00
16.00
15.00
14.00
30
100
40
50
60
50
60
70
Relative Humidity (%)
Temperature
90
100
80
90
100
June month
Temperature ºC
Tem perature ºC
May month
40.00
39.00
38.00
37.00
36.00
35.00
34.00
33.00
32.00
31.00
30.00
29.00
28.00
27.00
26.00
25.00
24.00
23.00
22.00
21.00
20.00
19.00
18.00
17.00
16.00
15.00
14.00
40
80
Temperature
Temperature
30
70
Relative Humidity(%)
Relative Humidity(%)
80
90
100
40.00
39.00
38.00
37.00
36.00
35.00
34.00
33.00
32.00
31.00
30.00
29.00
28.00
27.00
26.00
25.00
24.00
23.00
22.00
21.00
20.00
19.00
18.00
17.00
16.00
15.00
14.00
30
40
50
60
70
Relative Humidity (%)
Temperature
Figure 6.16: Plotting of the indoor space temperature and indoor the relative
humidity of the indoor living space of the test house, within summer
comfort zone according month (March, April, May and June).
March remains within comfort temperature range. From the figure 6.16
majority points of March are located at low humidity zone with the comfort
temperature in summer season. April and May is the hottest month in Bangladesh,
during this period in May very few points are located out of upper limit of comfort
temperature zone (24ºC-32ºC, in still air condition) but below the highest tolerance
range 36ºC with air flow 0.45 m/s (Mallick, 1994). In June when climatic conditions
are hot and wet, some points started to scatter towards higher regime of Rh 90%
because of rainfall increased from this month. And only 2% points (as half month
data taken up to 20 June) are outside of the upper limit of comfort zone (relative
humidity 50% to 95%). Relative humidity chronologically increases from March to
June, which also influences to improve the indoor comfort environment.
145
From the above findings it is evident that the thermal performance of upper
space and better thermal comfort quality of indoor living environment in traditional
house of Bangladesh is acceptable. So in the context of Dhaka city within a very
worst situation, the comfort thermal condition at the traditional house is still
tolerable.
6.8.2
Evaluation of the Indoor Comfort during Winter Season
TemperatureºC
Winter season
40.00
39.00
38.00
37.00
36.00
35.00
34.00
33.00
32.00
31.00
30.00
29.00
28.00
27.00
26.00
25.00
24.00
23.00
22.00
21.00
20.00
19.00
18.00
17.00
16.00
15.00
14.00
20
30
40
50
60
70
80
90
Relative Humidity (%)
Figure 6.17: Plotting of the indoor temperature and indoor relative humidity of the
indoor living space within winter comfort zone (January and February)
Winter is a very short period (only three months) in Bangladesh. According
to climatic condition winter is cool and dry. According to previous climatic study
winter season generally remains within comfort temperature range in Bangladesh
(Hossain and Nooruddin, 1993).
The diagram for comfort analysis for the tested Bangladesh traditional house
at Dhaka city illustrates that, concentrated points are scatter within the comfort zone.
A concentration can be traced between 45%-70% relative humidity and 19.5ºC to
23ºC temperature.
From the above analyses it is evident that the thermal performance of upper
space, with different percentage of window openings in upper space provides a better
146
thermal comfort quality of indoor living environment in traditional houses is also
acceptable in winter season.
6.9
Role of Upper space During Winter and Summer Season
6.9.1
Winter Season during Himalayan Cold Wind Flow.
The upper space plays a vital role for controlling the indoor living space
temperature within a comfort range. From the table 6.3 (when the Himalayan cold
wind flow in winter season) according to air temperature difference the relationship
between outdoor temperature (To), upper space temperature (Tu) and indoor
temperature (Ti) derive that, during day time Ti<Tu>To and at night time Ti>Tu<To.
In the month of January when Himalayan cold wind blows, night becomes
very misty. During this period a lot of dew formed over the outer C.I sheet roof, in
every night of experiment. At night upper space losses heat because of the C.I sheet
roof surface temperature dropped significantly below the ambient air temperature.
This phenomenon influences the upper space air temperature. So the upper space is
cooler than indoor living spaces and outdoors.
147
Ti<Tu>To
Figure 6.18
Ti>Tu<To
Heat flow pattern, during day and night when Himalayan cold wind
flow occur in winter (Ti= indoor temperature, Tu= upper space
temperature, To= outdoor temperature)
During day time, Tu become hotter than Ti and To then heat flows from Tu
to Ti and To because of solar radiation and clear sky (0.6 octas, cloud coverage).
During this period in day time, Ti is lower than Tu but remains within comfort
temperature range.
At night when Tu becomes minimum, then Ti and To remain warmer than
upper space temperature. From the table 6.3 it is realized that at 6am the air
temperature become the minimum. During day time heat is stored in the upper space
and at night upper space starts to transmit the heat towards the indoor and outdoor.
By this process the indoor becomes hotter than the upper space, which is desirable
for winter nights.
6.9.2
Winter Season during Common Weather Condition.
From the table 6.5 (which is common weather condition of winter season)
according to air temperature difference, the relationship between outdoor, upper
148
space and indoor indicates that, during day time Ti<Tu<To and at night time
Ti>Tu>To.
During day time it was observed that the increase of To (outdoor temperature)
influences the Tu (upper temperature). Tu is hotter than Ti (indoor temperature)
which means heat flow from Tu to Ti. So during day time the closed windows of the
upper space, worked as a buffer in winter seasons, which gain heat from outdoor and
store the heat for a long time. The heat is then transmitted into the indoor living
space and that makes the indoor environment in comfortable range.
Ti<Tu<To
Figure 6.19
Ti>Tu>To
Heat flow pattern during day and night in general weather condition
in winter
For better performance this research assumes that during winter season if the
window openings in upper space is open after sunrise and closed before sunset, then
the indoor thermal environment of the Bangladesh traditional house will be more
comfortable. Because of windows are closed during day time the upper space did
not gain heat by convection from outdoor. Upper space becomes hottest at 3pm. So
when upper space windows were opened, the conduction and convection heat flow
influence the upper space to be hot during day time and it can store heat for winter
night.
149
After sunset when To cool down then Tu is hotter than To and Ti. So at that
time, heat starts to transmit to the indoor space from upper space. After sunset the
indoor gain heat from upper space, which helps the indoor environment warmer than
outdoor till to sunrise (6 am) and this phenomena is desirable for winter night.
6.9.3
Summer Season during 0% Window Opening in Upper Space
In summer season during day time when upper space windows are used for
cooling process, prevention of incoming solar radiation through window is done by
closing windows in the day. For closed windows, heat gain by convection becomes
less in upper space. So Tu is hotter than Ti. During this period only conduction heat
flows from direct solar radiation. And it passed through To to Tu and from Tu to Ti
and chronologically heat loss by night trapped cool air in upper space and wooden
ceiling of the test house.
Ti<Tu<To
Figure 6.20
Ti>Tu>To
Heat flow pattern during day and night 0% opening condition in
summer
So in summer day time, Ti is smaller then To. This is a desirable condition
for comfort environment in summer day time. Upper space is influenced by solar
radiant temperature, as it obstructs the major passage of incoming heat through the
150
upper space to the indoor space and help to reduce radiant temperature to ensure
thermal comfort in indoor living space of traditional house.
At night, upper space with closed window acts as heat storage. So it will take
a long time to be cooled down and the upper space influences the indoor temperature
to rise for longer time in winter.
For this reason when outdoor ambient air
temperature becomes cooler at the same time Ti and Tu are hotter than To. Because
of closed windows in upper space, this creates a buffer to heat loss by long wave
radiation and convectional heat loss.
6.9.4
Summer Season during 25% and 75% Opening in Upper Space
In the summer season, when upper space window openings are used for
cooling process then during day time, the upper space and indoor living space
thermal environment become hotter than thermal environment of upper space with
closed windows because of incoming solar radiation through C.I sheet roof and by
windows convectional heat gain from ambient air from outdoor, influence the indoor
space temperature to increase. With the increase of opening percentage of upper
space (25% to 75%) the indoor air temperature also becomes warmer than outdoor
ambient environment.
Ti<Tu>To
Figure 6.21
Ti>Tu<To
Heat flow pattern during day and night condition in summer
151
Table 6.15
Relation between temperature difference of indoor, outdoor and upper
space with different percentage of window opening in upper space
Season
Month
window
opening of
upper space
March
0 % percent
April
25 % percent
Summer
May
June
75 % percent
75 % percent
Condition
Day Max
Night Min
Day Max
Night Min
Day Max
Night Min
Day Max
Night Min
Temp.
diff.
Ti & To
%
10.46
17.60
4.56
7.08
2.38
5.74
6.83
2.90
Relation
Between
Ti,& To
Ti<To
Ti>To
Ti<To
Ti>To
Ti>To
Ti<To
Ti<To
Ti>To
Relation
Between
Ti, Tu, &
To
Ti<Tu<To
Ti>Tu>To
Ti<Tu>To
Ti>Tu<To
Ti<Tu>To
Ti>Tu<To
Ti<Tu>To
Ti>Tu>To
From the relationship between Ti<Tu>To and according to table 6.15 during
day time with 25% and 75% opening the temperature relationship of indoor, outdoor
and upper space are same.
During summer night, with 25% and 75% openings, the relationship is
Ti>Tu<To can be expected for most of the period at night when upper space radiant
temperature is below than outdoor ambient air temperature. With 75% window
openings in the upper space this creates more comfortable indoor environment
compare to 25% opening of windows in the upper space. More openings allow more
convectional heat loss with ambient air and long wave radiation cooling at night. So
at night Tu become cooler than To and Ti. However, Tu takes heat from Ti and
makes indoor comfortable.
6.10
Conclusion
The above mentioned findings established that the traditional house in
Bangladesh with upper space attains more comfortable indoor environment in the
context of dense Gulshan area at Dhaka city. A number of important phenomenons
have been found from the analysis and have been presented mostly in graph form for
152
easy understanding. However, before those may be taken accepted and useful for the
built-form designers, there is a need to recheck those especially on the context of
dense Dhaka city in which those were achieved. These will be addressed in the next
chapter to prove then the results of analysis and findings have a strong and scientific
base.
CHAPTER 7
CONCLUSION
This chapter concludes the research 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
setout in chapter 1. Finally, further investigations related to this study are suggested.
7.1
Review of Thesis Objectives and Research Questions
The aim of the study is to investigate the performance of traditional house
roof section with the following objective:
It is also to evaluate the thermal performance of traditional house roof section
of Bangladesh with different percentage of window openings of upper space during
winter and summer season in the context of Dhaka city. The following questions
were addressed in this thesis:
1. How upper space plays a vital role with diurnal variation of ambient
environment?
2. What is the thermal performance of traditional house in Bangladesh which is
influenced by the upper space during winter and summer season with
different percentage of window opening?
154
3.
Does the traditional house provide thermal comfort in context of dense
environment of Dhaka city?
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:
7.2.1
The Vital role of Upper Space with Diurnal Variation of Ambient
Environment
The characteristic of the traditional house, according to climatic responses
are done through the use of lightweight materials, window opening in upper space,
house orientation and layout. The thermal environment in the test house with respect
to upper space is closely related with lightweight C.I. sheet roof and also its physical
position, any temperature fluctuation on C.I sheet roof directly and immediately
affects the upper space air temperature.
The outer C.I sheet roof is directly exposed to sky. In winter season during
night time the upper space works as heat storage. Because when windows of upper
space are totally closed, during day time the upper spaces work as buffer and it
absorbs heat from direct solar radiation and at night it influences indoor to be warm
up quickly after sunset and the upper spaces transmit heat to indoors.
This
phenomenon works as a warming system for winter season in Bangladesh traditional
house at Dhaka city.
During summer, the upper space has to be insulated from the sun and hot
ambient air during daytime (with close window) which results in minimization of
heat gain from the outdoor environment and night time by long wave radiation and
155
convection with ambient air, the upper spaces emit the heat quickly to the outdoors
and indoors.
So the indoors become uncomfortable which is undesirable. This
undesirable condition depends on the percentage of window openings which when
more are opened in upper space, then the indoor is more uncomfortable. Therefore,
this system has to be incorporated by the opening the windows closing them at the
upper spaces, which is opened during night and remain close in day time for better
thermal performance during summer.
At night time with 0% window openings, the upper space acts as a hot
storage in both summer and winter seasons and it increases the indoor temperature.
This condition is effective for the winter seasons to maintain the indoor thermal
comfort at night time but not acceptable for summer nights.
But at night in
traditional house, window opening of upper space functions as a cold storage which
is needed for summer seasons and it is more effective for summer seasons but it is
not preferred for winter nights.
The upper space of the traditional house in Bangladesh has a provision of
operable windows which can perform as an efficient combined radiator and as
cooing element. So the upper space has a natural successful implementation of
cooling concept.
7.2.2
The thermal performance of traditional house in Bangladesh which
influenced by the upper space during winter and summer season with
different percentage of window opening.
The upper space contains C.I. sheet in outer surface and wooden planks in the
base and air gap height between them is 2.1m.
This combination shows a
phenomenon that have optimize to the thermal performance of traditional houses in
Bangladesh. The exterior roofs and walls of the house are enveloped in C.I. sheets
which has a low thermal capacity and immediately gains heat and with low time lag.
It is alternately heated during day and cooled at night by long wave radiation. Part
of the heat absorbed during the day warms the mass of the house and only the
156
remainder passes to the interior. During the summer and in warm regions, the
external surface (particularly C.I. sheet roof) temperature is above the internal level
(wooden plank) during day time and it becomes lower at night. Here, in addition to
its quantitative effect on heat exchange, the temperature between outdoors and
indoors may also have a qualitative influence on the direction of heat flow.
Therefore, the upper space performance was evaluated by temperature disparity
between upper space and indoor temperature. One of the intensions of providing
percentage of upper opening was to reduce storage of heat in the upper space at day
time so there was less possibility of heat emission to indoor environment. According
to thermal performance summary, mean maximum and mean minimum of upper,
outdoor and indoor temperature in summer of the test house are shown in table 7.1.
Table 7.1
Tabular format of minimum and maximum temperature in both
seasons of indoor, outdoor and upper space
Season
Location
Temp. Max. ºC
Temp. Min. ºC
Winter
Outdoor
Indoor
Upper
27.71
26.57
27.28
19.6
19.07
18.83
Summer
Outdoor
Indoor
Upper
36.29
33.63
35.51
25.11
26.54
25.55
.
It is evident from the table 7.1, that mean maximum temperature difference
between indoor and outdoor in winter season, indoor living space is almost 1ºC
lower than outdoor during day time and during night time indoor temperature is
almost 1ºC higher than outdoor. In summer seasons indoor is almost 3 ºC lower than
outdoor in day time and during night time indoor temperature is almost 1ºC higher
than outdoor but it is within comfort temperature range. So for summer days,
traditional houses are more effective for indoor comfort environment but outdoor
and upper space temperature remains out of comfort temperature range. Indoor is
also 1ºC higher than comfort temperature range which can be tolerable with
increasing air flow. The mean minimum temperature profile at night for both
summer and winter remains are within comfort temperature range.
157
Table 7.2
Daily Maximum and minimum temperature difference with different
percentage of upper space window opening in winter and summer season
Season
Month
January
12th
Winter
February
10th
Window opening
of upper space
0 % percent
Himalayan wind
cold flow
0 % percent
Common
condition
March
8th
0 % percent
April
2nd
25 % percent
May
7th
75 % percent
Summer
June
19th
75 % percent
Condition
Temp. diff.
(To-Ti)/ To
%
Relation
Between
Ti,& To
Relation
Between
Ti, Tu, &
To
Day Max
2.46
Ti<To
Ti<Tu>To
Night Min
3.67
Ti>To
Ti>Tu<To
Day Max
3.22
Ti<To
Ti<Tu<To
Night Min
12.68
Ti>To
Ti>Tu>To
Day Max
10.46
Ti<To
Ti<Tu<To
Night Min
17.60
Ti>To
Ti>Tu>To
Day Max
4.56
Ti<To
Ti<Tu>To
Night Min
7.08
Ti>To
Ti>Tu<To
Day Max
2.38
Ti>To
Ti<Tu>To
Night Min
5.74
Ti<To
Ti>Tu<To
6.83
2.90
Ti<To
Ti<Tu>To
Ti>To
Ti>Tu>To
Day Max
Night Min
From the table 7.2 it is summarized that when upper space window opening’s
percentage increases than indoor and outdoor temperature difference decreases
during summer day time. But the upper space temperature chronologically becomes
higher in respect of percentage increasing of upper space window opening. The
difference between indoor and outdoor temperature decrease because of heat starts to
transmit from hot upper spaces to cool indoor living spaces. According to this
phenomenon from the tabulation, it is indicated that it has sufficient difference
between indoor and outdoor temperatures during summer nights. So the upper space
influences the indoor living space for heat gain and heat loss. Finally, it is suggested
for better performance of the traditional house in Bangladesh during summer seasons,
the window of upper spaces should be closed before sunrise and should be opened as
early as possible after sunset. During winter season closed window in upper space is
desirable for better thermal performance.
158
7.2.3
The traditional house in context of dense Dhaka city still Comfortable
for Summer and Winter
In a wide range of climatic conditions for winter after Givoni (Figure 4.2),
Sharma and Ali (1986) suggested the temperature range is from 17 ºC to 32 ºC while
humidity range is fixed in lower limit 25% to upper limit 80% (Mallick, 1994;
Mridha, 2002).
The evaluation of indoor comfort zone for summer season in Bangladesh is
based on analyses of temperature and Rh value. The comfort temperature range is
24ºC to 32ºC while humidity range is 50% to 95%, in a condition with no air
movement (Mallick, 1994; Mridha, 2002).
The thermal performance of traditional house capability was indicated by,
long period of thermal comfort duration in indoor of the traditional house is justified
by considering sunrise and sunset times as discussed in table 7.3
Table 7.3
The tabular format of thermal comfort duration in indoor of
traditional house
Season
Winter
Month
Time
Window
Opening
Comfortable
hours within 12
hours
comfortable
range in %
January
After sunrise to sunset
0%
12
100
12
100
12
100
12
100
12
100
12
100
4
33
12
100
4
33
12
100
6
50
12
100
After sunset to sunrise
February
After sunrise to sunset
0%
After sunset to sunrise
March
After sunrise to sunset
0%
After sunset to sunrise
April
Summer
After sunrise to sunset
25%
After sunset to sunrise
May
After sunrise to sunset
75%
After sunset to sunrise
June
After sunrise to sunset
After sunset to sunrise
75%
159
From table 7.3, it is summarized that the traditional house of Bangladesh has
a better ability to provide a thermal comfort environment in indoor living space
during night time for summer and winter season. During day time if the window
opening of upper space increases then indoor become uncomfortable for 7-8 hours
starting from 10am to 5pm when maximum activity is done outside of the house.
According to winter comfort zone (Mallick, 1994; Abu Mukim Mridha, 2002)
relation between indoor air temperature and relative humidity of the test house with
winter comfort zone of only 2% temperature points are out of the comfort zone and
according to summer comfort zone (Mallick, 1994) only 9% temperature points are
out of comfort zone. The compactness of surroundings was affecting the traditional
houses and in uncomfortable hot in Dhaka. So it is evident, that a more desirable
environmental condition exists in the traditional house. By keeping the originality of
the traditional house, it can contribute to providing the natural thermal comfort for
people although the house lies in the high density environment during both summer
and winter season.
7.3
Research result
The research found that the Bangladesh traditional houses still have a better
ability in providing the thermal comfort especially at a dense environment such as
Dhaka city in Bangladesh. It is proved that the indoor living space environment is
comfortable in both summer and winter seasons during night time. Research results
further more indicate that to achieve better thermal performance in Bangladesh for
traditional houses, during winter season, windows of upper space for both day and
night time used to be closed. During the summer seasons, the window openings of
upper space need to be kept closed as early as possible after sunrise and open after
sunsets. This study concludes that the use of upper spaces in Bangladesh traditional
houses has a significant impact on the thermal performance and thus it makes the
traditional house more efficient and sustainable.
160
7.4
Suggestions for Further Research
It is evident from all above circumstances that traditional houses of
Bangladesh has interesting natural climate controlling features such as upper spaces.
In this research, the upper space demonstrates a better thermal performance with
respect to its different percentage of window opening control in different seasonal
environmental conditions are better in terms of comfort in the test room. During
summer daytime, upper space influences the indoor to an uncomfortable
environment (7-8 hours, from 10am to 5 pm) but after sunset, indoor becomes
comfortable in a very short time. Performance evaluation between the summer and
winter seasons with different percentage of openings and without openings confirms
that upper plays a vital role to controlling the indoor thermal comfort environment of
the traditional house in Bangladesh for both summer and winter seasons in Dhaka.
For better performance of the traditional house this research has few potential areas
of concern.
1)
Influence of window openings during winter seasons.
2)
The thermal performance on other types of traditional house in
Bangladesh.
3)
The thermal performance of the traditional house by open the window
opening of upper space during the winter seasons.
4)
The evaluation of height of the upper space by simulation process for
better performance of traditional houses.
5)
The material of roofs and walls for better performance of traditional
houses.
6)
Implementation of the upper space as the roof of contemporary
building.
161
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xxv
APPENDICES
A
Equipment Details
166
B
Data From HOBO Data Logger
171
C
Bangladesh Meteorological Department Weather
184
Data
D
Per mints Temperature Data
187
E
Previous Study
192
F
Publications
198
166
Appendix A
167
168
169
170
171
Appendix B
From Hobo Data Logger download Graphical file of January.
From Hobo Data Logger download Graphical file of February.
172
From Hobo Data Logger download Graphical file of January per week.
From Hobo Data Logger download Graphical file of January per week.
173
From Hobo Data Logger download Graphical file of January per week.
From Hobo Data Logger download Graphical file of February per week.
From Hobo Data Logger download Graphical file of February per week.
174
From Hobo Data Logger download Graphical file of February per week.
175
From Hobo Data Logger download Graphical file of February per week.
From Hobo Data Logger download Graphical file of February per week.
176
From Hobo Data Logger download Graphical file of March per week.
From Hobo Data Logger download Graphical file of March per week.
177
From Hobo Data Logger download Graphical file of March per week.
From Hobo Data Logger download Graphical file of March per week.
178
From Hobo Data Logger download Graphical file of March per week.
From Hobo Data Logger download Graphical file of April per week.
179
From Hobo Data Logger download Graphical file of April per week.
From Hobo Data Logger download Graphical file of April per week.
180
From Hobo Data Logger download Graphical file of April per week.
From Hobo Data Logger download Graphical file of May per week.
181
From Hobo Data Logger download Graphical file of May per week.
From Hobo Data Logger download Graphical file of May per week.
182
From Hobo Data Logger download Graphical file of May per week.
From Hobo Data Logger download Graphical file of June per week.
183
From Hobo Data Logger download Graphical file of June per week.
184
Appendix C
From Bangladesh Meteorological department data of Yearly Cloud Amount
From Bangladesh Meteorological department data of Yearly Average Dry bulb
Temperature
185
From Bangladesh Meteorological department data of Yearly Average Humidity
From Bangladesh Meteorological department data of Yearly Average wind
speed
186
From Bangladesh Meteorological department data of Yearly Total Rain fall
187
Appendix D
OUTDOOR TEMPARATURE
Date/Time
01/08/07
19:30:22.0
01/08/07
19:31:22.0
01/08/07
19:32:22.0
RH
(%)
c:1 2
Temperature
(*C) c:*3
UPPER TEMPARATURE
Date/Time
20.95
01/08/07
19:30:00.0
48.4
20.95
01/08/07
19:31:00.0
49
20.95
01/08/07
19:32:00.0
47.8
01/08/07
19:33:22.0
49.6
20.95
01/08/07
19:33:00.0
01/08/07
19:34:22.0
50.3
20.95
01/08/07
19:34:00.0
RH
(%)
c:1 2
Temperature
(*C) c:*4
INDOOR TEMPARATURE
Date/Time
RH
(%)
c:1 2
Temperature
(*C) c:*4
20.57
01/08/07
19:30:22.0
47.8
20.95
59.6
20.19
01/08/07
19:31:22.0
48.4
20.95
58.2
20.19
01/08/07
19:32:22.0
49
20.95
56.5
20.19
01/08/07
19:33:22.0
49.6
20.95
55.2
20.19
01/08/07
19:34:22.0
50.3
20.95
59
01/08/07
19:35:22.0
51.1
20.95
01/08/07
19:35:00.0
55.5
19.81
01/08/07
19:35:22.0
51.1
20.95
01/08/07
19:36:22.0
51.9
20.95
01/08/07
19:36:00.0
56.2
19.81
01/08/07
19:36:22.0
51.9
20.95
01/08/07
19:37:22.0
52.7
20.95
01/08/07
19:37:00.0
56.7
19.42
01/08/07
19:37:22.0
52.7
20.95
57.3
19.42
01/08/07
19:38:22.0
53.1
20.95
57.8
19.42
01/08/07
19:39:22.0
53.4
20.95
53.8
20.95
54.4
20.57
01/08/07
19:38:22.0
53.1
20.95
01/08/07
19:38:00.0
01/08/07
19:39:22.0
53.4
20.95
01/08/07
19:39:00.0
58.3
19.04
01/08/07
19:40:22.0
58.8
19.04
01/08/07
19:41:22.0
01/08/07
19:40:22.0
53.8
21.33
01/08/07
19:40:00.0
01/08/07
19:41:22.0
54.4
20.95
01/08/07
19:41:00.0
01/08/07
19:42:22.0
55
20.95
01/08/07
19:42:00.0
59.2
19.04
01/08/07
19:42:22.0
55
20.57
01/08/07
19:43:22.0
55.4
20.95
01/08/07
19:43:00.0
59.4
19.04
01/08/07
19:43:22.0
55.4
20.57
01/08/07
19:44:22.0
55.6
20.95
01/08/07
19:44:00.0
60
19.04
01/08/07
19:44:22.0
55.6
20.57
60
19.04
01/08/07
19:45:22.0
55.9
20.57
60.3
19.04
01/08/07
19:46:22.0
56.3
20.57
01/08/07
19:45:22.0
55.9
20.95
01/08/07
19:45:00.0
01/08/07
19:46:22.0
56.3
20.95
01/08/07
19:46:00.0
60.6
19.04
01/08/07
19:47:22.0
56.8
20.57
60.9
19.04
01/08/07
19:48:22.0
57
20.57
01/08/07
19:47:22.0
56.8
20.95
01/08/07
19:47:00.0
01/08/07
19:48:22.0
57
20.95
01/08/07
19:48:00.0
01/08/07
19:49:22.0
57.4
20.95
01/08/07
19:49:00.0
61.2
19.04
01/08/07
19:49:22.0
57.4
20.19
01/08/07
19:50:22.0
57.5
20.95
01/08/07
19:50:00.0
61.2
19.04
01/08/07
19:50:22.0
57.5
20.19
01/08/07
19:51:22.0
57.8
20.95
01/08/07
19:51:00.0
61.5
19.04
01/08/07
19:51:22.0
57.8
20.19
61.9
19.04
01/08/07
19:52:22.0
57.8
20.19
61.9
19.04
01/08/07
19:53:22.0
58
20.19
01/08/07
19:52:22.0
57.8
20.95
01/08/07
19:52:00.0
01/08/07
19:53:22.0
58
20.95
01/08/07
19:53:00.0
62
19.04
01/08/07
19:54:22.0
58
20.19
62.3
19.04
01/08/07
19:55:22.0
58
20.57
01/08/07
19:54:22.0
58
20.95
01/08/07
19:54:00.0
01/08/07
19:55:22.0
58
20.57
01/08/07
19:55:00.0
62.3
19.04
01/08/07
19:56:22.0
58.6
20.57
62.6
19.04
01/08/07
19:57:22.0
59.7
20.57
01/08/07
19:56:22.0
58.6
20.57
01/08/07
19:56:00.0
01/08/07
19:57:22.0
59.7
20.19
01/08/07
19:57:00.0
01/08/07
19:58:22.0
60.3
19.42
01/08/07
19:58:00.0
62.6
19.04
01/08/07
19:58:22.0
60.3
20.57
01/08/07
19:59:22.0
60.9
19.04
01/08/07
19:59:00.0
63
19.04
01/08/07
19:59:22.0
60.9
20.57
01/08/07
20:00:22.0
61.5
19.04
01/08/07
20:00:00.0
63
19.04
01/08/07
20:00:22.0
61.5
20.57
63
19.04
01/08/07
20:01:22.0
61.9
20.19
63.3
19.04
01/08/07
20:02:22.0
62.2
20.19
62.6
20.19
63
20.19
01/08/07
20:01:22.0
61.9
19.04
01/08/07
20:01:00.0
01/08/07
20:02:22.0
62.2
18.66
01/08/07
20:02:00.0
63.3
19.04
01/08/07
20:03:22.0
63.3
19.04
01/08/07
20:04:22.0
01/08/07
20:03:22.0
62.6
18.66
01/08/07
20:03:00.0
01/08/07
20:04:22.0
63
18.66
01/08/07
20:04:00.0
01/08/07
20:05:22.0
63
18.28
01/08/07
20:05:00.0
63.3
19.04
01/08/07
20:05:22.0
63
20.19
01/08/07
20:06:22.0
63.3
18.66
01/08/07
20:06:00.0
63.3
19.04
01/08/07
20:06:22.0
63.3
20.19
01/08/07
20:07:22.0
63.3
18.28
01/08/07
20:07:00.0
63.3
19.04
01/08/07
20:07:22.0
63.3
20.19
63.3
19.04
01/08/07
20:08:22.0
63.7
20.19
63.7
19.04
01/08/07
20:09:22.0
63.7
20.19
01/08/07
20:08:22.0
63.7
18.28
01/08/07
20:08:00.0
01/08/07
20:09:22.0
63.7
18.28
01/08/07
20:09:00.0
63.7
19.04
01/08/07
20:10:22.0
63.7
20.19
63.7
19.04
01/08/07
20:11:22.0
63.7
20.19
01/08/07
20:10:22.0
63.7
18.28
01/08/07
20:10:00.0
01/08/07
20:11:22.0
63.7
18.66
01/08/07
20:11:00.0
63.7
19.04
01/08/07
20:12:22.0
63.7
20.19
63.7
19.04
01/08/07
20:13:22.0
63.7
20.19
19.04
01/08/07
20:14:22.0
64.1
20.19
01/08/07
20:12:22.0
63.7
18.28
01/08/07
20:12:00.0
01/08/07
20:13:22.0
63.7
18.66
01/08/07
20:13:00.0
18.66
01/08/07
20:14:00.0
01/08/07
20:14:22.0
64.1
63.7
188
01/08/07
20:15:22.0
64.1
18.28
01/08/07
20:15:00.0
63.7
19.04
01/08/07
20:15:22.0
64.1
20.19
01/08/07
20:16:22.0
64.1
18.28
01/08/07
20:16:00.0
64.1
19.04
01/08/07
20:16:22.0
64.1
20.19
01/08/07
20:17:22.0
64.1
18.28
01/08/07
20:17:00.0
64.1
19.04
01/08/07
20:17:22.0
64.1
20.19
01/08/07
20:18:22.0
64.1
18.28
01/08/07
20:18:00.0
64.1
19.04
01/08/07
20:18:22.0
64.1
20.19
01/08/07
20:19:22.0
64.1
18.66
01/08/07
20:19:00.0
64.1
19.04
01/08/07
20:19:22.0
64.1
20.19
64.1
19.04
01/08/07
20:20:22.0
64.1
20.19
64.1
19.04
01/08/07
20:21:22.0
64.5
20.19
01/08/07
20:20:22.0
64.1
18.28
01/08/07
20:20:00.0
01/08/07
20:21:22.0
64.5
18.28
01/08/07
20:21:00.0
64.1
19.04
01/08/07
20:22:22.0
64.5
20.19
64.1
19.04
01/08/07
20:23:22.0
64.1
20.19
01/08/07
20:22:22.0
64.5
18.66
01/08/07
20:22:00.0
01/08/07
20:23:22.0
64.1
18.28
01/08/07
20:23:00.0
01/08/07
20:24:22.0
64.1
18.28
01/08/07
20:24:00.0
64.1
19.04
01/08/07
20:24:22.0
64.1
20.19
01/08/07
20:25:22.0
64.1
18.28
01/08/07
20:25:00.0
64.1
19.04
01/08/07
20:25:22.0
64.1
20.19
01/08/07
20:26:22.0
64.1
18.28
01/08/07
20:26:00.0
64.1
19.04
01/08/07
20:26:22.0
64.1
20.19
64.1
19.04
01/08/07
20:27:22.0
64.5
20.19
64.1
19.04
01/08/07
20:28:22.0
64.5
20.19
01/08/07
20:27:22.0
64.5
18.28
01/08/07
20:27:00.0
01/08/07
20:28:22.0
64.5
18.28
01/08/07
20:28:00.0
64.1
19.04
01/08/07
20:29:22.0
64.5
20.19
64.1
19.04
01/08/07
20:30:22.0
64.5
20.19
01/08/07
20:29:22.0
64.5
18.28
01/08/07
20:29:00.0
01/08/07
20:30:22.0
64.5
18.28
01/08/07
20:30:00.0
64.1
19.04
01/08/07
20:31:22.0
64.5
20.19
64.1
19.04
01/08/07
20:32:22.0
64.5
20.19
01/08/07
20:31:22.0
64.5
18.28
01/08/07
20:31:00.0
01/08/07
20:32:22.0
64.5
18.28
01/08/07
20:32:00.0
01/08/07
20:33:22.0
64.1
18.28
01/08/07
20:33:00.0
64.1
19.04
01/08/07
20:33:22.0
64.1
20.19
01/08/07
20:34:22.0
64.1
18.28
01/08/07
20:34:00.0
64.1
19.04
01/08/07
20:34:22.0
64.1
20.19
01/08/07
20:35:22.0
64.5
18.28
01/08/07
20:35:00.0
64.1
19.04
01/08/07
20:35:22.0
64.5
20.19
64.1
19.04
01/08/07
20:36:22.0
64.5
20.19
64.5
19.04
01/08/07
20:37:22.0
64.1
20.19
01/08/07
20:36:22.0
64.5
18.28
01/08/07
20:36:00.0
01/08/07
20:37:22.0
64.1
18.28
01/08/07
20:37:00.0
64.5
19.04
01/08/07
20:38:22.0
64.5
20.19
64.5
19.04
01/08/07
20:39:22.0
64.5
20.19
01/08/07
20:38:22.0
64.5
18.28
01/08/07
20:38:00.0
01/08/07
20:39:22.0
64.5
18.28
01/08/07
20:39:00.0
01/08/07
20:40:22.0
64.2
17.9
01/08/07
20:40:00.0
64.5
19.04
01/08/07
20:40:22.0
64.2
20.19
01/08/07
20:41:22.0
64.2
17.9
01/08/07
20:41:00.0
64.5
19.04
01/08/07
20:41:22.0
64.2
19.81
01/08/07
20:42:22.0
64.1
17.9
01/08/07
20:42:00.0
64.5
19.04
01/08/07
20:42:22.0
64.1
20.19
64.9
19.04
01/08/07
20:43:22.0
64.2
19.81
64.9
19.04
01/08/07
20:44:22.0
64.2
19.81
01/08/07
20:43:22.0
64.2
17.9
01/08/07
20:43:00.0
01/08/07
20:44:22.0
64.2
17.9
01/08/07
20:44:00.0
64.9
19.04
01/08/07
20:45:22.0
63.8
19.81
64.9
19.04
01/08/07
20:46:22.0
64.2
19.81
01/08/07
20:45:22.0
63.8
17.9
01/08/07
20:45:00.0
01/08/07
20:46:22.0
64.2
17.9
01/08/07
20:46:00.0
64.9
19.04
01/08/07
20:47:22.0
64.2
19.81
64.9
19.04
01/08/07
20:48:22.0
64.2
19.81
01/08/07
20:47:22.0
64.2
18.28
01/08/07
20:47:00.0
01/08/07
20:48:22.0
64.2
17.9
01/08/07
20:48:00.0
01/08/07
20:49:22.0
64.2
17.9
01/08/07
20:49:00.0
65
19.04
01/08/07
20:49:22.0
64.2
19.81
01/08/07
20:50:22.0
64.6
17.9
01/08/07
20:50:00.0
65
19.04
01/08/07
20:50:22.0
64.6
19.81
01/08/07
20:51:22.0
64.6
18.28
01/08/07
20:51:00.0
65
19.04
01/08/07
20:51:22.0
64.6
19.81
64.9
18.66
01/08/07
20:52:22.0
64.6
19.81
65
19.04
01/08/07
20:53:22.0
64.2
19.81
01/08/07
20:52:22.0
64.6
17.9
01/08/07
20:52:00.0
01/08/07
20:53:22.0
64.2
17.9
01/08/07
20:53:00.0
65
19.04
01/08/07
20:54:22.0
63.8
19.81
65
18.66
01/08/07
20:55:22.0
63.8
19.81
01/08/07
20:54:22.0
63.8
17.9
01/08/07
20:54:00.0
01/08/07
20:55:22.0
63.8
17.9
01/08/07
20:55:00.0
01/08/07
20:56:22.0
63.8
17.9
01/08/07
20:56:00.0
65
18.66
01/08/07
20:56:22.0
63.8
19.81
01/08/07
20:57:22.0
63.8
17.9
01/08/07
20:57:00.0
65.4
18.66
01/08/07
20:57:22.0
63.8
19.81
01/08/07
20:58:22.0
63.4
17.9
01/08/07
20:58:00.0
65.4
18.66
01/08/07
20:58:22.0
63.4
19.81
65
18.66
01/08/07
20:59:22.0
63.4
19.81
65.4
18.66
01/08/07
21:00:22.0
63.4
19.81
01/08/07
20:59:22.0
63.4
17.9
01/08/07
20:59:00.0
01/08/07
21:00:22.0
63.4
17.9
01/08/07
21:00:00.0
65.4
18.66
01/08/07
21:01:22.0
63.4
19.81
65.4
18.66
01/08/07
21:02:22.0
63.4
19.81
63.4
19.81
63.4
19.81
01/08/07
21:01:22.0
63.4
17.9
01/08/07
21:01:00.0
01/08/07
21:02:22.0
63.4
17.9
01/08/07
21:02:00.0
65.4
18.66
01/08/07
21:03:22.0
65.4
18.66
01/08/07
21:04:22.0
01/08/07
21:03:22.0
63.4
17.9
01/08/07
21:03:00.0
01/08/07
21:04:22.0
63.4
17.9
01/08/07
21:04:00.0
189
01/08/07
21:05:22.0
63.4
17.9
01/08/07
21:05:00.0
65.4
18.66
01/08/07
21:05:22.0
63.4
19.81
01/08/07
21:06:22.0
63.4
17.9
01/08/07
21:06:00.0
65.4
18.66
01/08/07
21:06:22.0
63.4
19.81
01/08/07
21:07:22.0
63.4
17.9
01/08/07
21:07:00.0
65.4
18.66
01/08/07
21:07:22.0
63.4
19.81
01/08/07
21:08:22.0
63.4
17.9
01/08/07
21:08:00.0
65.4
18.66
01/08/07
21:08:22.0
63.4
19.81
01/08/07
21:09:22.0
63.4
17.9
01/08/07
21:09:00.0
65.4
18.66
01/08/07
21:09:22.0
63.4
19.81
65.4
18.66
01/08/07
21:10:22.0
63.1
19.81
65.4
18.66
01/08/07
21:11:22.0
63.4
19.81
01/08/07
21:10:22.0
63.1
17.9
01/08/07
21:10:00.0
01/08/07
21:11:22.0
63.4
17.9
01/08/07
21:11:00.0
65.4
18.66
01/08/07
21:12:22.0
63.4
19.81
65.8
18.66
01/08/07
21:13:22.0
63.4
19.81
01/08/07
21:12:22.0
63.4
17.9
01/08/07
21:12:00.0
01/08/07
21:13:22.0
63.4
17.9
01/08/07
21:13:00.0
01/08/07
21:14:22.0
63.1
17.9
01/08/07
21:14:00.0
65.8
18.66
01/08/07
21:14:22.0
63.1
19.81
01/08/07
21:15:22.0
63.1
17.9
01/08/07
21:15:00.0
65.8
18.66
01/08/07
21:15:22.0
63.1
19.81
01/08/07
21:16:22.0
63.4
17.9
01/08/07
21:16:00.0
65.8
18.66
01/08/07
21:16:22.0
63.4
19.81
65.8
18.66
01/08/07
21:17:22.0
63.4
19.81
65.8
18.66
01/08/07
21:18:22.0
63.4
19.81
01/08/07
21:17:22.0
63.4
17.9
01/08/07
21:17:00.0
01/08/07
21:18:22.0
63.4
17.9
01/08/07
21:18:00.0
65.8
18.66
01/08/07
21:19:22.0
63.8
19.81
65.8
18.66
01/08/07
21:20:22.0
63.8
19.81
01/08/07
21:19:22.0
63.8
17.9
01/08/07
21:19:00.0
01/08/07
21:20:22.0
63.8
17.9
01/08/07
21:20:00.0
65.8
18.66
01/08/07
21:21:22.0
63.8
19.81
65.8
18.66
01/08/07
21:22:22.0
64.2
19.81
01/08/07
21:21:22.0
63.8
17.9
01/08/07
21:21:00.0
01/08/07
21:22:22.0
64.2
17.9
01/08/07
21:22:00.0
01/08/07
21:23:22.0
63.8
17.9
01/08/07
21:23:00.0
65.8
18.66
01/08/07
21:23:22.0
63.8
19.81
01/08/07
21:24:22.0
64.2
17.9
01/08/07
21:24:00.0
65.8
18.66
01/08/07
21:24:22.0
64.2
19.81
01/08/07
21:25:22.0
64.2
17.9
01/08/07
21:25:00.0
65.8
18.66
01/08/07
21:25:22.0
64.2
19.81
65.8
18.66
01/08/07
21:26:22.0
64.2
19.81
65.8
18.66
01/08/07
21:27:22.0
63.9
19.81
01/08/07
21:26:22.0
64.2
17.9
01/08/07
21:26:00.0
01/08/07
21:27:22.0
63.9
17.9
01/08/07
21:27:00.0
65.8
18.66
01/08/07
21:28:22.0
64.2
19.81
65.8
18.66
01/08/07
21:29:22.0
64.2
19.81
01/08/07
21:28:22.0
64.2
17.9
01/08/07
21:28:00.0
01/08/07
21:29:22.0
64.2
17.9
01/08/07
21:29:00.0
01/08/07
21:30:22.0
64.2
17.9
01/08/07
21:30:00.0
65.8
18.66
01/08/07
21:30:22.0
64.2
19.81
01/08/07
21:31:22.0
64.2
17.9
01/08/07
21:31:00.0
65.8
18.66
01/08/07
21:31:22.0
64.2
19.81
01/08/07
21:32:22.0
64.2
17.9
01/08/07
21:32:00.0
65.8
18.66
01/08/07
21:32:22.0
64.2
19.81
66.2
18.66
01/08/07
21:33:22.0
64.2
19.81
66.2
18.66
01/08/07
21:34:22.0
64.2
19.81
01/08/07
21:33:22.0
64.2
17.9
01/08/07
21:33:00.0
01/08/07
21:34:22.0
64.2
17.9
01/08/07
21:34:00.0
66.2
18.66
01/08/07
21:35:22.0
64.2
19.81
66.2
18.66
01/08/07
21:36:22.0
64.2
19.81
01/08/07
21:35:22.0
64.2
17.9
01/08/07
21:35:00.0
01/08/07
21:36:22.0
64.2
17.9
01/08/07
21:36:00.0
66.7
18.66
01/08/07
21:37:22.0
64.2
19.81
66.2
18.66
01/08/07
21:38:22.0
64.2
19.81
01/08/07
21:37:22.0
64.2
17.9
01/08/07
21:37:00.0
01/08/07
21:38:22.0
64.2
17.9
01/08/07
21:38:00.0
01/08/07
21:39:22.0
64.6
17.9
01/08/07
21:39:00.0
66.2
18.66
01/08/07
21:39:22.0
64.6
19.81
01/08/07
21:40:22.0
64.6
17.9
01/08/07
21:40:00.0
66.7
18.66
01/08/07
21:40:22.0
64.6
19.81
01/08/07
21:41:22.0
64.6
17.9
01/08/07
21:41:00.0
66.7
18.66
01/08/07
21:41:22.0
64.6
19.81
66.7
18.66
01/08/07
21:42:22.0
64.6
19.81
66.7
18.66
01/08/07
21:43:22.0
64.6
19.81
01/08/07
21:42:22.0
64.6
17.9
01/08/07
21:42:00.0
01/08/07
21:43:22.0
64.6
17.9
01/08/07
21:43:00.0
66.7
18.66
01/08/07
21:44:22.0
64.6
19.81
67.1
18.66
01/08/07
21:45:22.0
64.6
19.81
01/08/07
21:44:22.0
64.6
17.9
01/08/07
21:44:00.0
01/08/07
21:45:22.0
64.6
17.9
01/08/07
21:45:00.0
01/08/07
21:46:22.0
64.6
17.9
01/08/07
21:46:00.0
66.7
18.66
01/08/07
21:46:22.0
64.6
19.81
01/08/07
21:47:22.0
64.6
17.9
01/08/07
21:47:00.0
66.7
18.66
01/08/07
21:47:22.0
64.6
19.81
01/08/07
21:48:22.0
64.6
17.9
01/08/07
21:48:00.0
67.1
18.66
01/08/07
21:48:22.0
64.6
19.81
67.1
18.66
01/08/07
21:49:22.0
64.6
19.81
67.2
18.66
01/08/07
21:50:22.0
65
19.81
01/08/07
21:49:22.0
64.6
17.9
01/08/07
21:49:00.0
01/08/07
21:50:22.0
65
17.9
01/08/07
21:50:00.0
67.2
18.66
01/08/07
21:51:22.0
65
19.81
67.2
18.66
01/08/07
21:52:22.0
65
19.81
65
19.81
65
19.81
01/08/07
21:51:22.0
65
17.9
01/08/07
21:51:00.0
01/08/07
21:52:22.0
65
17.9
01/08/07
21:52:00.0
67.2
18.28
01/08/07
21:53:22.0
67.2
18.28
01/08/07
21:54:22.0
01/08/07
21:53:22.0
65
17.9
01/08/07
21:53:00.0
01/08/07
21:54:22.0
65
17.9
01/08/07
21:54:00.0
190
01/08/07
21:55:22.0
65
17.9
01/08/07
21:55:00.0
67.2
18.28
01/08/07
21:55:22.0
65
19.81
01/08/07
21:56:22.0
65
17.9
01/08/07
21:56:00.0
67.2
18.28
01/08/07
21:56:22.0
65
19.81
01/08/07
21:57:22.0
65
17.9
01/08/07
21:57:00.0
67.2
18.66
01/08/07
21:57:22.0
65
19.81
01/08/07
21:58:22.0
65
17.9
01/08/07
21:58:00.0
67.2
18.66
01/08/07
21:58:22.0
65
19.81
01/08/07
21:59:22.0
65
17.9
01/08/07
21:59:00.0
67.2
18.66
01/08/07
21:59:22.0
65
19.81
67.2
18.28
01/08/07
22:00:22.0
65
19.81
67.2
18.28
01/08/07
22:01:22.0
65
19.81
01/08/07
22:00:22.0
65
17.9
01/08/07
22:00:00.0
01/08/07
22:01:22.0
65
17.9
01/08/07
22:01:00.0
67.2
18.28
01/08/07
22:02:22.0
65
19.81
67.2
18.28
01/08/07
22:03:22.0
65
19.81
01/08/07
22:02:22.0
65
17.9
01/08/07
22:02:00.0
01/08/07
22:03:22.0
65
17.9
01/08/07
22:03:00.0
01/08/07
22:04:22.0
65
17.52
01/08/07
22:04:00.0
67.2
18.28
01/08/07
22:04:22.0
65
19.81
01/08/07
22:05:22.0
65
17.52
01/08/07
22:05:00.0
67.7
18.28
01/08/07
22:05:22.0
65
19.81
01/08/07
22:06:22.0
65
17.9
01/08/07
22:06:00.0
67.7
18.28
01/08/07
22:06:22.0
65
19.81
68.2
18.28
01/08/07
22:07:22.0
65
19.81
68.2
18.28
01/08/07
22:08:22.0
65
19.81
65
19.81
65
19.81
01/08/07
22:07:22.0
65
17.9
01/08/07
22:07:00.0
01/08/07
22:08:22.0
65
17.9
01/08/07
22:08:00.0
68.7
18.28
01/08/07
22:09:22.0
68.7
18.28
01/08/07
22:10:22.0
01/08/07
22:09:22.0
65
17.9
01/08/07
22:09:00.0
01/08/07
22:10:22.0
65
17.52
01/08/07
22:10:00.0
68.7
18.28
01/08/07
22:11:22.0
65
19.81
68.7
18.28
01/08/07
22:12:22.0
65.4
19.81
01/08/07
22:11:22.0
65
17.52
01/08/07
22:11:00.0
01/08/07
22:12:22.0
65.4
17.52
01/08/07
22:12:00.0
01/08/07
22:13:22.0
65.4
17.52
01/08/07
22:13:00.0
68.7
18.28
01/08/07
22:13:22.0
65.4
19.81
01/08/07
22:14:22.0
65
17.52
01/08/07
22:14:00.0
68.7
18.28
01/08/07
22:14:22.0
65
19.81
01/08/07
22:15:22.0
65
17.52
01/08/07
22:15:00.0
68.7
18.28
01/08/07
22:15:22.0
65
19.81
68.7
18.28
01/08/07
22:16:22.0
65.4
19.81
68.7
18.28
01/08/07
22:17:22.0
65.4
19.81
01/08/07
22:16:22.0
65.4
17.52
01/08/07
22:16:00.0
01/08/07
22:17:22.0
65.4
17.9
01/08/07
22:17:00.0
68.7
18.28
01/08/07
22:18:22.0
65.4
19.81
69.2
18.28
01/08/07
22:19:22.0
65.4
19.81
01/08/07
22:18:22.0
65.4
17.9
01/08/07
22:18:00.0
01/08/07
22:19:22.0
65.4
17.52
01/08/07
22:19:00.0
01/08/07
22:20:22.0
65.4
17.52
01/08/07
22:20:00.0
69.2
18.28
01/08/07
22:20:22.0
65.4
19.81
01/08/07
22:21:22.0
65.4
17.52
01/08/07
22:21:00.0
69.2
18.28
01/08/07
22:21:22.0
65.4
19.81
01/08/07
22:22:22.0
65.4
17.52
01/08/07
22:22:00.0
69.2
18.28
01/08/07
22:22:22.0
65.4
19.81
69.2
18.28
01/08/07
22:23:22.0
65.4
19.81
69.2
18.28
01/08/07
22:24:22.0
65.4
19.42
01/08/07
22:23:22.0
65.4
17.52
01/08/07
22:23:00.0
01/08/07
22:24:22.0
65.4
17.52
01/08/07
22:24:00.0
69.2
18.28
01/08/07
22:25:22.0
65.4
19.42
69.2
18.28
01/08/07
22:26:22.0
65.4
19.42
01/08/07
22:25:22.0
65.4
17.52
01/08/07
22:25:00.0
01/08/07
22:26:22.0
65.4
17.52
01/08/07
22:26:00.0
69.2
18.28
01/08/07
22:27:22.0
65.4
19.42
69.8
18.28
01/08/07
22:28:22.0
65.4
19.42
01/08/07
22:27:22.0
65.4
17.52
01/08/07
22:27:00.0
01/08/07
22:28:22.0
65.4
17.52
01/08/07
22:28:00.0
01/08/07
22:29:22.0
65.4
17.52
01/08/07
22:29:00.0
69.2
18.28
01/08/07
22:29:22.0
65.4
19.42
01/08/07
22:30:22.0
65.4
17.52
01/08/07
22:30:00.0
69.2
18.28
01/08/07
22:30:22.0
65.4
19.42
01/08/07
22:31:22.0
65.4
17.52
01/08/07
22:31:00.0
69.2
18.28
01/08/07
22:31:22.0
65.4
19.42
69.2
18.28
01/08/07
22:32:22.0
65.4
19.42
69.8
18.28
01/08/07
22:33:22.0
65.4
19.42
01/08/07
22:32:22.0
65.4
17.52
01/08/07
22:32:00.0
01/08/07
22:33:22.0
65.4
17.52
01/08/07
22:33:00.0
69.8
18.28
01/08/07
22:34:22.0
65.4
19.81
69.8
18.28
01/08/07
22:35:22.0
65.4
19.42
01/08/07
22:34:22.0
65.4
17.52
01/08/07
22:34:00.0
01/08/07
22:35:22.0
65.4
17.52
01/08/07
22:35:00.0
01/08/07
22:36:22.0
65.4
17.52
01/08/07
22:36:00.0
69.8
18.28
01/08/07
22:36:22.0
65.4
19.42
01/08/07
22:37:22.0
65.4
17.52
01/08/07
22:37:00.0
69.8
18.28
01/08/07
22:37:22.0
65.4
19.42
01/08/07
22:38:22.0
65.4
17.52
01/08/07
22:38:00.0
69.8
18.28
01/08/07
22:38:22.0
65.4
19.42
69.8
18.28
01/08/07
22:39:22.0
65.4
19.42
69.2
18.28
01/08/07
22:40:22.0
65.4
19.42
01/08/07
22:39:22.0
65.4
17.52
01/08/07
22:39:00.0
01/08/07
22:40:22.0
65.4
17.52
01/08/07
22:40:00.0
69.3
18.28
01/08/07
22:41:22.0
65.4
19.42
69.2
18.28
01/08/07
22:42:22.0
65.4
19.42
65.4
19.42
65.4
19.42
01/08/07
22:41:22.0
65.4
17.52
01/08/07
22:41:00.0
01/08/07
22:42:22.0
65.4
17.52
01/08/07
22:42:00.0
69.2
18.28
01/08/07
22:43:22.0
69.3
18.28
01/08/07
22:44:22.0
01/08/07
22:43:22.0
65.4
17.52
01/08/07
22:43:00.0
01/08/07
22:44:22.0
65.4
17.52
01/08/07
22:44:00.0
191
01/08/07
22:45:22.0
65.4
17.52
01/08/07
22:45:00.0
69.9
18.28
01/08/07
22:45:22.0
65.4
19.42
01/08/07
22:46:22.0
65.4
17.52
01/08/07
22:46:00.0
69.9
18.28
01/08/07
22:46:22.0
65.4
19.42
01/08/07
22:47:22.0
65.4
17.52
01/08/07
22:47:00.0
70.5
18.28
01/08/07
22:47:22.0
65.4
19.42
01/08/07
22:48:22.0
65.4
17.52
01/08/07
22:48:00.0
69.9
18.28
01/08/07
22:48:22.0
65.4
19.42
01/08/07
22:49:22.0
65.4
17.52
01/08/07
22:49:00.0
69.9
18.28
01/08/07
22:49:22.0
65.4
19.42
69.9
18.28
01/08/07
22:50:22.0
65.4
19.42
69.9
18.28
01/08/07
22:51:22.0
65.4
19.42
01/08/07
22:50:22.0
65.4
17.52
01/08/07
22:50:00.0
01/08/07
22:51:22.0
65.4
17.52
01/08/07
22:51:00.0
70.5
18.28
01/08/07
22:52:22.0
65.4
19.42
70.5
18.28
01/08/07
22:53:22.0
65.4
19.42
01/08/07
22:52:22.0
65.4
17.52
01/08/07
22:52:00.0
01/08/07
22:53:22.0
65.4
17.52
01/08/07
22:53:00.0
01/08/07
22:54:22.0
65.4
17.52
01/08/07
22:54:00.0
71.1
18.28
01/08/07
22:54:22.0
65.4
19.42
01/08/07
22:55:22.0
65.4
17.52
01/08/07
22:55:00.0
70.5
18.28
01/08/07
22:55:22.0
65.4
19.42
01/08/07
22:56:22.0
65.4
17.52
01/08/07
22:56:00.0
70.5
18.28
01/08/07
22:56:22.0
65.4
19.42
71.1
18.28
01/08/07
22:57:22.0
65.4
19.42
70.5
18.28
01/08/07
22:58:22.0
65.4
19.42
01/08/07
22:57:22.0
65.4
17.52
01/08/07
22:57:00.0
01/08/07
22:58:22.0
65.4
17.52
01/08/07
22:58:00.0
70.5
18.28
01/08/07
22:59:22.0
65.4
19.42
70.5
18.28
01/08/07
23:00:22.0
65.4
19.42
01/08/07
22:59:22.0
65.4
17.52
01/08/07
22:59:00.0
01/08/07
23:00:22.0
65.4
17.52
01/08/07
23:00:00.0
70.5
18.28
01/08/07
23:01:22.0
65.4
19.42
70.5
18.28
01/08/07
23:02:22.0
65.4
19.42
01/08/07
23:01:22.0
65.4
17.52
01/08/07
23:01:00.0
01/08/07
23:02:22.0
65.4
17.52
01/08/07
23:02:00.0
01/08/07
23:03:22.0
65.5
17.52
01/08/07
23:03:00.0
70.5
18.28
01/08/07
23:03:22.0
65.5
19.42
01/08/07
23:04:22.0
65.5
17.52
01/08/07
23:04:00.0
71.1
18.28
01/08/07
23:04:22.0
65.5
19.42
01/08/07
23:05:22.0
65.4
17.52
01/08/07
23:05:00.0
71.1
18.28
01/08/07
23:05:22.0
65.4
19.42
71.1
18.28
01/08/07
23:06:22.0
65.5
19.42
71.1
18.28
01/08/07
23:07:22.0
65.4
19.42
01/08/07
23:06:22.0
65.5
17.52
01/08/07
23:06:00.0
01/08/07
23:07:22.0
65.4
17.52
01/08/07
23:07:00.0
71.7
18.28
01/08/07
23:08:22.0
65.4
19.42
71.7
18.28
01/08/07
23:09:22.0
65.4
19.42
01/08/07
23:08:22.0
65.4
17.52
01/08/07
23:08:00.0
01/08/07
23:09:22.0
65.4
17.52
01/08/07
23:09:00.0
01/08/07
23:10:22.0
65.5
17.52
01/08/07
23:10:00.0
71.7
18.28
01/08/07
23:10:22.0
65.5
19.42
01/08/07
23:11:22.0
65.5
17.52
01/08/07
23:11:00.0
71.7
18.28
01/08/07
23:11:22.0
65.5
19.42
01/08/07
23:12:22.0
65.5
17.52
01/08/07
23:12:00.0
71.7
18.28
01/08/07
23:12:22.0
65.5
19.42
71.7
18.28
01/08/07
23:13:22.0
65.5
19.42
71.1
18.28
01/08/07
23:14:22.0
65.5
19.42
01/08/07
23:13:22.0
65.5
17.52
01/08/07
23:13:00.0
01/08/07
23:14:22.0
65.5
17.52
01/08/07
23:14:00.0
71.1
18.28
01/08/07
23:15:22.0
65.5
19.42
71.1
18.28
01/08/07
23:16:22.0
65.5
19.42
01/08/07
23:15:22.0
65.5
17.52
01/08/07
23:15:00.0
01/08/07
23:16:22.0
65.5
17.52
01/08/07
23:16:00.0
71.1
18.28
01/08/07
23:17:22.0
65.5
19.42
71.1
18.28
01/08/07
23:18:22.0
65.5
19.42
01/08/07
23:17:22.0
65.5
17.52
01/08/07
23:17:00.0
01/08/07
23:18:22.0
65.5
17.52
01/08/07
23:18:00.0
01/08/07
23:19:22.0
65.5
17.52
01/08/07
23:19:00.0
70.5
17.9
01/08/07
23:19:22.0
65.5
19.42
01/08/07
23:20:22.0
65.5
17.52
01/08/07
23:20:00.0
70.5
17.9
01/08/07
23:20:22.0
65.5
19.42
01/08/07
23:21:22.0
65.5
17.52
01/08/07
23:21:00.0
70.5
17.9
01/08/07
23:21:22.0
65.5
19.42
70.5
17.9
01/08/07
23:22:22.0
65.5
19.42
70.5
17.9
01/08/07
23:23:22.0
65.5
19.42
01/08/07
23:22:22.0
65.5
17.14
01/08/07
23:22:00.0
01/08/07
23:23:22.0
65.5
17.14
01/08/07
23:23:00.0
71.1
17.9
01/08/07
23:24:22.0
65.5
19.42
71.1
17.9
01/08/07
23:25:22.0
65.5
19.42
01/08/07
23:24:22.0
65.5
17.14
01/08/07
23:24:00.0
01/08/07
23:25:22.0
65.5
17.14
01/08/07
23:25:00.0
01/08/07
23:26:22.0
65.5
17.14
01/08/07
23:26:00.0
71.1
17.9
01/08/07
23:26:22.0
65.5
19.42
01/08/07
23:27:22.0
65.5
17.14
01/08/07
23:27:00.0
71.1
17.9
01/08/07
23:27:22.0
65.5
19.42
01/08/07
23:28:22.0
65.5
17.14
01/08/07
23:28:00.0
71.1
17.9
01/08/07
23:28:22.0
65.5
19.42
71.1
17.9
01/08/07
23:29:22.0
65.5
19.42
71.1
17.9
01/08/07
23:30:22.0
65.5
19.42
01/08/07
23:29:22.0
65.5
17.14
01/08/07
23:29:00.0
01/08/07
23:30:22.0
65.5
17.14
01/08/07
23:30:00.0
192
Appendix E
(i) Karmokar et. al’s study on the basis of about 30 years (1960-1990) data
regarding variability and probabilistic extremities of climates elements in Dhaka
(Karmokar,et al,1993) researcher made the following observations:
(a) The mean maximum temperature over Dhaka has its lowest value in
January and progresses as the season progresses. It becomes maximum in April with
a decreasing tendency up to August. The mean temperature increases from January
to April, then remains almost constant up to September, and decreases up to January.
The mean minimum temperature is the lowest in January, increases up to June and
remains fairly constant up to September and decreases after that.
(b) The mean prevailing wind speed is minimum in January and maximum in
April (No mention of directions).
(c) The mean rainfall increases sharply from January and attains maximum
value in June and July, after which it decreases.
(d) The mean relative Humidity has higher values during the southwest
monsoon and then decreases sharply up to March.
(e) The probabilistic high values of monthly highest maximum temperature
in April are 39.1°, 40.2° and 41.0° C in one year out of 4, 10 and 25 years
respectively. The probabilistic low values of monthly lowest minimum temperature
are 7.4°, 6.40 and 5.6° C in the same scale.
(f) The probabilistic high values of maximum wind speed in 1 case out of 25
cases are 108 kph, 123 kph and 100 kph in March, April and May respectively (no
mention of directions).
(g) The months of December, January and February are the most comfortable
months in Dhaka, where as April through October are uncomfortable months.
193
(ii). Hossain et al’s study on Discomfort Index for measuring climatic
comfort Discomfort Index (D,I.) was suggested by Thom's as:
D.I.= 0.4(Td +Tw)+15,
where Td and Tw, stand for Dry bulb and wet bulb temperature respectively in °F
scale. In °C scale it comes to be,
D.I.= 0.72 (Td + Tw) + 40.6.
The comfort situation of Bangladesh in terms of Discomfort Index (D. I.) has been
expressed as the result of one researcher in the following way:
(a) MARCH TO MAY: Regarding time, the original work was done using
UTC, which
corresponds to GMT and is less than Bangladesh Standard Time BST
by six hours. For easy understanding Bangladesh Standard Time BST has been used
here).
At 6.00 A.M. BST, Dhaka (whole Bangladesh) is generally comfortable. Evening
Hours 6.00 P.M. BST: Dhaka (and northern half of Bangladesh) is generally
comfortable. In April, rest of the country falls under discomfort with D.I value
exceeding 75.
(b) JUNE TO SEPTEMBER: 6.00 A.M. BST: Dhaka (whole Bangladesh) is
generally under discomfort with D.I. Index exceeding 75. The weather is hot and
dry,
6.00 P.M. BST: Dhaka (whole of Bangladesh) is under discomfort, with D.1. Index
exceeding 80.
(c) OCTOBER TO NOVEMBER: 6.00 A.M. BST: Dhaka (whole
Bangladesh) is generally under discomfort with D. I. Index exceeding 75. 6.00 P.M.
BST. Dhaka (whole of Bangladesh) is under partial discomfort, with high value in
D.I. Index.
(d) DECEMBER TO FEBRUARY: 6.00 A.M BST: In January and February
Dhaka is under comfort zone with low D.I. Index. 6.00 P. M.: Dhaka is under
comfort zone with low D.I. Index.
194
The D.I. Index of Dhaka city calculated by using Thorn's index and using
climatic data from the meteorological Department at different months at specified
time has been shown in Tables 4.3 and Table 4.4below:
Table 4.3
Discomfort index for Dhaka at 6.00 am
DISCOMFORT INDEX FOR DHAKA FOR 1991-92 AT 6.00 A.M.
BANGLADESH STANDARD TIME
MONTH
TIME
D.I. INDEX
COMMENT
January
6.00 A. M. BST
60
Within comfort range
February
6.00 A. M. BST
69
Within comfort range
March
6.00 A. M. BST
70
Within comfort range
April
6.00 A. M. BST
74
Within comfort range
May
6.00 A. M. BST
76
Uncomfortable
June
6.00 A. M. BST
79
Uncomfortable
July
6.00 A. M. BST
79
Uncomfortable
August
6.00 A. M. BST
79
Uncomfortable
September
6.00 A. M. BST
78
Uncomfortable
October
6.00 A. M. BST
76
Uncomfortable
November
6.00 A. M. BST
68
Within comfort range
December
6.00 A. M. BST
62
Within comfort range
Source: HUMAN COMFORT IN THE URBAN AREAS OF BANGLADESH in Technical
Conference on Urban Tropical Climates 1993.
195
Table 4.4
Discomfort index for Dhaka at 6.00 pm
DISCOMFORT INDEX FOR DHAKA FOR 1991-92 AT 6.00 P.M.
BANGLADESH STANDARD TIME
MONTH
TIME
D.I. INDEX
COMMENT
January
6.00 P. M. BST
60
Within comfort range
February
6.00 P.M. BST
72
Within comfort range
March
6.00 P.M. BST
77
Uncomfortable
April
6.00 P.M. BST
79
Uncomfortable
May
6.00 P. M. BST
81
Uncomfortable
June
6.00 P.M. BST
82
Uncomfortable
July
6.00 P.M. BST
81
Uncomfortable
August
6.00 P.M. BST
81
Uncomfortable
September
6.00 P.M. BST
80
Uncomfortable
October
6.00 P.M. BST
79
Uncomfortable
November
6.00 P.M. BST
74
Within comfort range
December
6.00 P.M. BST
67
Within comfort range
Source: Hossain, Akram. Paper: HUMAN COMFORT IN THE URBAN AREAS OF
BANGLADESH in Technical Conference on Urban Tropical Climates 1993.
(iii) Hossain et al’s study on general climate on the basis of 40 years (19511990) climatic data of Dhaka city researcher has prepared the following information
(Ershad et al, 1993):
(a). After sunrise, the day temperature increases at attains maximum value at
3.00 P.M. BST. The day temperature in urban area is higher than sub-urban and
rural areas. The night temperature in rural areas is lower than urban areas.
(b). The relative humidity decreases at daytime and increases at night, the minimum value being at 3.00 P.M. BST,
when the day temperature is maximum.
196
(c). Urbanization has profound effect in reducing the wind speed.
(d). The heat island effect is less prominent, the intensity being 2.5º in April
and 0.6º in July. The less prominence is due to high humidity and surface wind.
(e) Relative humidity is found inversely related to the local intensity of urban heat
island in Dhaka.
(f) Total incoming solar radiation in Dhaka city is found about 12% lower
than that in the rural areas.
(g) The amount of precipitation is higher in Dhaka city except in August.
(iv) Khaleque et al’s study on Micro-climate of Dhaka city: One group of
researchers on the basis of their studies on Temperature and Humidity (Khaleque,
1993) conducted in 10 points, viz. (01) Agargaon, (02) tejgaon, (03) Motijheel,(04)
Dhanmondi, (05) Nawabgonj, (06) Mirpur, (07) Kallyanpur, (08) Gulshan, (09)
Bakshi bazaar and (10) Airport, commented:
(a). On January 03, 1992 at 6.00 A.M. BST several warm pockets were
discovered at Tejgaon Industrial Area, Motijheel Commercial and congested part of
old Dhaka.
(b). The cool areas were at Agargaon, Dhanmondi and Zia International
Airport.
(c). The maximum intensity of heat island or warm pocket was found in the
order of 3.8° C in Old Dhaka and Motijheel Commercial Area.
(d). During summer months (June 08,1992) heat island intensity was in the
order of 0.08° C.
197
From the above observations they drew the following deductions:
(a) During winter month’s maximum intensity of heat island in the order of
3.8° C is observed.
(b) Two peaks of heat island intensity are observed one at early morning and
another early night, but the early morning heat island is stronger.
(c) The heat island or warm pockets found over the densely populated
residential and high-rise building construction area. The cool areas are found over
the well ventilated planned residential areas.
(d) During summer months heat island effect is insignificant.
(e) Humidity island has an inverse relation to heat island whenever moisture
is less, but lowed heat island intensity whenever moisture is high.
198
Appendix F
PUBLICATIONS
Conference Paper 1
Rumana Rashid, Prof. Dr. Mohd. Hamdan Bin Ahmed and Dr.Dilshan
Remaz Ossen, (2007). “Thermal performance by the Traditional Roof Section in
Bangladesh” 8th Senvar & 2nd Malay Architecture Conference, Sustainability in Rain,
Sun and Wind, 23rd -24th,August, 2007,Surabaya, Indonesia.
Abstract
Traditional house reflects socio-cultural heritage of peoples and also encapsulate
traditional forms values. Traditional houses are influencing by the local available
materials and climate to achieve comfort. Bangladesh is an agricultural country. So
culturally people need to store their corns and other necessary households during the
monsoon period. According to solve this problem people made a double layer roof
section in the traditional house, which is known as locally ‘Upper’ or ‘Dartala’. This
roof section plays a vital roll to create a comfortable environment in indoor of the
house. During the summer time, the contemporary architecture of Bangladesh
becomes very uncomfortable to stay in the top floor. On the other hand, in the
traditional houses, roof section is used in which the outer roof material is made of
corrugated iron sheet and the internal roof material is of wooden planks. During
daytime, this roof section becomes hot but after sunset, it becomes cool in a very
short time. Currently, set of HOBO data logger was installed in one model of
traditional Bangladesh house in Dhaka for collecting data. This paper highlights the
methodology of thermal performance of the traditional roof section in the context of
Dhaka during summer and winter season.
Keyword: roof section, thermal comfort
199
Conference Paper 2
Rumana Rashid, Prof. Dr. Mohd. Hamdan Bin Ahmed and Dr.Dilshan
Remaz Ossen,, (2007). “Traditional House of Bangladesh : Typology of House
According to Material and Location”,
Virtual Conference on Sustainable
Architectural Design and Urban Planning, Asia Sustainability Net.upc.edu., 15th 24th ,September, 2007.
Abstract
Traditional Houses represent the heritage of a country and also reflects traditional
forms and values, fundamental to the culture of the people of that country. It
possesses distinct characteristics as regards planning, use of materials and location.
Like urban architecture, traditional house is also subject to change but in Bangladesh
traditional house has clung to tradition. It has not really changed until recently. For
centuries traditional house has been using locally available materials. It is only from
that late 19th century that traditional house began to change in the use of housing
materials. Traditional architecture in Bangladesh was largely built without formally
trained professionals. Buildings were built by construction workers. Any architect or
planner never designed traditional house. The full planning concept has been
developed by the people according to need. This traditional house has been changed
along with time to fulfil the demand of the user. At the same time planning concept
was constant. The aim of this paper is to get natural design principles of different
type of traditional houses in Bangladesh according to availability of local materials.
The different kinds of house are developed in different regions of Bangladesh such
as mud house, bamboo house, stilts house and timber house. Many designer are now
interested in adapting traditional feature to modern design but such attempts have
had limited success because traditional house design have themselves not been
clearly understood. This study can help to convey a good understanding by analysing
different types of traditional house in Bangladesh.
Keywords: traditional house, typology, local materials, location, climate.