Energy Efficient Glass Façade for
building envelope
Sri Ram.N – IGBC AP; GRIHA Trainer
Saint Gobain Glass India
15th June 2011
Glass for building envelope
• Indispensible construction material
• Freedom from conventional building shapes, with
unmatched aesthetics.
• Transparent to visible light – daylighting of interiors
• Blending of interiors with exteriors
• Helps to maintain hygienic environment with easy
maintenance
• Glass is 100% recyclable – Sustainable building envelope
Consumption Pattern
Others
Television 10%
Lighting
28%
4%
Refrigeration
13%
RESIDENTIAL
Airconditioner
45%
Equipment
15%
Lighting
20%
Ventilation
5%
COMMERCIAL
Source: Res :UNEP SBCI & TERI Study, Comm:
IGDB Study
80 % of Building
Energy Consumption
Airconditioner
60%
Key Performance Factors
Lighting Energy
• Light Transmission
Cooling Energy
• Total Heat Gain / Heat Transmission
– SHGC or SF : Solar Heat Gain Coefficient or Solar Factor
– U Value
Performance Parameter
Light Factors
Visual Light Transmission (VLT)
• Percentage of incident light transmitted
• Percentage transmission depends Tint &
Coating
out
Light Transmitted
Factors affecting Visual Light Transmission (VLT)
Single Glazed
Unit
Single Glazed
Unit
Single Glazed
Unit
Single Glazed
Single Glazed
Clear
Unit
Green tint
Unit
Blue Tint
VLT = 89%
Clear - Solar control
VLT = 73%
Green - Solar control
VLT = 57%
VLT = 67% – 7%
VLT = 54% – 6%
Energy Performance Factors
Total Heat Gain / Heat Transferred
-SHGC
-U Value
Total Heat Gain
Electromagnetic Spectrum at Terrestrial Level
TOTAL HEAT GAIN
Amount of heat
Transferred due to
temperature difference
Heat Gain due to
direct solar radiation
Near Infra Red
UV Visible
.25 .38
.78
Far Infra Red
2.50
Wave Length
50 µ
Heat gain
due to Direct
solar radiation
directly +
re-emitted energy
= S F / SHGC
1#
2#
directly transmitted
energy
reflected
energy
re-emitted
energy
re-emitted
energy
Factors affecting SOLAR FACTOR (SF) or Solar Heat Gain Coefficient
(SHGC)
Single Glazed
Unit
Single Glazed
Unit
Clear
Green
SHGC = 0.84
SHGC = 0.56
Single Glazed
Unit
Blue
SHGC = 0.56
Single Glazed Unit
Single Glazed Unit
Clear –solar control
Green–solar control
SHGC = 0.15 – 0.68
SHGC = 0.16– 0.47
Shading Coefficient
Shading Coefficient (SC) =
Solar factor of Glass
Solar factor of 3.0mm Clear Glass (0.87)
• SC should be used if the solar value are through 3mm clear glass
• SF or SHGC should be used if it is direct solar value from sun Eg: Weather Files
Amount of heat
Transferred due to
temperature difference
U Value
Area = 1 m2
U = 5.7 W/sqm K
T1 = 1 oC
T2 = 0 oC
Factors affecting U value
Inert
Gas
Single Glazed Unit
Double Glazed Unit
Double Glazed Unit
Double Glazed Unit
U value = 5.8W/SqmK
U value = 2.9W/SqmK
Low-e
Low-e + inert gas
U value = 1.4 to 2 W/SqmK
U value = 1.0 to 1.3 W/SqmK
ECBC – [Energy Conservation Building Code]
Glazing Requirements for building
envelope
ECBC Compliance Approach
• Prescriptive: component based approach
(specs given for each)
– Low Flexibility
– Easy Approach
• Trade Off: system based approach (trade off
between performance of envelope)
– Moderate Flexibility
– Comparatively Tedious Approach
• Performance Method: Whole Building Design
Analysis Approach (overall building energy
efficiency)
– High Flexibility
– Tedious Approach – High Detailing
Prescriptive
Compliance Approach
Climatic
zone map of
India
WWR: Window to wall ratio
Z
Case 1 : WWR = X / Y
Z
Case 2 : WWR = (X+Z) / Y
• WWR = Net Glazing area / Gross wall area
– Net glazing area (window area minus mullions and framing) divided by
– Gross exterior wall area (e.g., multiply width of the bay by floor-to-floor height)
• Spandrel Glass & Glass in front of dead wall are not considered as glass area
Prescriptive
Requirements
Light Transmission
SHGC / U value
ECBC Prescriptive requirements
Glass Performance
Light
transmission
Solar Control
U Value
89%
73%
Greater than 20%
0.84
0.55
Less than 0.25
5.7 W/SqmK
5.7 W/SqmK
Clear Glass
Tinted Glass
Less than 3.3
W/SqmK
ECBC Requirements
Coated Glass with Solar / Thermal
Insulation
Coating Technology
- Glass Conforming to ECBC
Compliance
C
O
A
T
I
N
G
Online
Coating
T
E
C
N
O
L
O
G
Y
Offline
Coating
CVD Coating
Manufactured during manufacturing of glass it self.
Process of manufacturing known as pyrolysis
Manufactured in a separate process (offline) by
Magnetron sputtering on to raw glass
Choosing “Correct” Glass
Energy Efficiency
Daylighting
Daylighting
Daylight Integration
Sunlight aids in,
– Reduction of Artificial lighting
– Increasing Vitamin D level
– Alleviate depression &anxiety
– Eliminates Claustrophobic effect
Glass,
– Allows abundant natural sunlight
– When compared to conventional
brick-mortar building, daylight
integration saves about 40 to 60%
of the energy used for lighting
– For a fixed lumen requirement,
sunlight generates lesser heat in
comparison to artificial lighting –
reduce the A/C bill
Light Heat ratio
Heat Built up
lumen
watts
Lumen / watts Hr
Indian Annual average
33330
364
91
Retrofits spiral CFLs
T5 luminaries
400
7
8
25
40
8
18
30
3
3
24
incandecent lamp
LED Lights
750
230
415
600
Clear Glass
Light Transmission
Average Lux Level
Peak Lux level
Outdoor Lux level : 9000Lux
Solar Control Coated Glass
89%
430 lux
1680 lux
Room Size : 4m X 5m
Light Transmission
Average Lux Level
Peak Lux level
30%
220 lux
670 lux
Window Size: 1.0mX 2.4m (WWR:20%)
Energy Efficiency
Air conditioned Spaces
Energy Analysis of air conditioned space
CASE
Solar
Factor
U Value
Light
W/m2K Transmis
sion
HVAC
Consumpt
ion kWh
Lighting
Consumpt
ion kWh
Total
kWh
Savings /
Year
kWh
1. Single Clear
0.83
5.7
89%
9574
551
10125
Base
3. Solar Control
0.30
5.7
30%
7017
595
7612
2513
Glass Performance on cooling & Lighting load
• Lower Solar Heat Gain coefficient significantly reduces the
cooling
•Optimized light transmission of glass reduces lighting energy
during daytime operation
Location: Mumbai
Floor area : 12000 Sqft WWR – 20%
Non - Air conditioned Spaces
Temperature Distribution
•
•
Case 1: Double Glazed Unit – Clear Glass
– Solar Factor
– U value
Case 2: Double Glazed Unit – Single silver Low-e
Glass
– Solar Factor
– U value
•
: 0.71
: 2.8W/SqmK
: 0.54
: 1.8W/SqmK
Case 3: Double Glazed Unit –Double silver Low-e
Glass
– Solar Factor
– U value
: 0.32
: 1.6W/SqmK
•
•
•
•
•
•
•
Location
:
Room Size
:
Glass Direction :
Glass Size
:
Over hang
:
Simulation
:
Simulation hours :
Mumbai
4m X 5m
South
1.9m X 4.6m
1.0m
Ecotect
8760 Hrs
Temperature Distribution
Duration
Comfort Temperature
Range
Double
Glazed Unit
Clear Glass
Double
Double
Glazed Unit
Glazed Unit
Single silvered
Double
low-e
silvered low-e
Temperature Range 20˚ – 30˚C
Hours
7457
7579
7756
%
86%
87.4%
88.5%
Increase in
comfort hours
Base
122 Hrs
299 Hrs
Temperature 32˚C
Discomfort Temperature
Range
Hours
1021
1007
957
%
11.7%
11.6%
10.9%
Temperature Range 34˚ – 36˚ C
Hours
282
174
47
%
3.25%
2.0%
0.53%
Go Green
• Do your little bit to the planet !
•
Every reduction in Unit of electricity (KwHr) means
1.4 kg (CO2e) per kWh*
• Every reduction in a single KWH, 1.4 Kg of CO2
emission is prevented
• Conversion factor includes GHG emission for handling, generation
& transportation loss
*Source: DEFRA – Dept of energy & climatic change