 |
|
Summer
Time
U-Value
|
Summer
Time
R-Value
|
Shading
Coefficient
|
Solar
Heat Gain
Coefficient
|
Visible
Light
Transmission
|
Coolness
Index
|
Ultraviolet
Light
Transmission
|
Relative
Heata Gain
Btu/Hr/ft
|
|
Clear Single Pane
|
1.03
|
0.97
|
1.00
|
0.89
|
90%
|
0.90
|
71%
|
214
|
|
Clear IG
|
0.55
|
1.82
|
0.89
|
0.78
|
81%
|
0.91
|
58%
|
188
|
|
Gray IG
|
0.55
|
1.82
|
0.73
|
0.62
|
55%
|
0.75
|
39%
|
151
|
|
Bronze IG
|
0.55
|
1.82
|
0.74
|
0.63
|
62%
|
0.84
|
42%
|
155
|
|
Sunglass IG
|
0.55
|
1.82
|
0.72
|
0.63
|
76%
|
1.06
|
52%
|
152
|
|
Low E IG
|
0.44
|
2.27
|
0.85
|
0.72
|
75%
|
0.88
|
47%
|
176
|
|
Evergreen TM IG
|
0.57
|
1.75
|
0.59
|
0.51
|
69%
|
1.17
|
23%
|
176
|
|
EnviroShield IG
|
0.30
|
3.33
|
0.47
|
0.33
|
72%
|
1.53
|
16%
|
98
|
|
 |
| EvergreenTM is a registered trademark of Libbey-Owens-Ford, Toledo, OH |
| EnviroShield is a registered trademark of Enlight Industries L.L.C. - Houston, TX |
| Sources: American Flat Glass, Cardinal CG, Libbey-Owens-Ford. Data based on 3/4" IG, DSB (1/8") Glass, and 1/2" airspace |
|
|
U-Value
|
|
The amount of heat transmitted by the window. The lower the number, the more efficient the window in reducing winter and summer heating/cooling costs.
|
|
| R-Value |
|
Designates a window's resistance to heat flow. The number is the inverse of the U-Value, the higher the number, the more efficient the window in reducing winter and summer heating/cooling costs.
|
|
| Shading Coefficient |
|
The ratio of solar heat gain through a glazing to the solar heat gain through a single lite of 1/8" glass. The smaller the number, the better the glazing is at preventing solar gain. The shading coefficient is specific to normal incidence angle and is being phased out in favor of solar heat gain coefficient. The lower the number, the more efficient the window is at reducing summer cooling costs.
|
|
| Solar Heat Gain Coefficient |
| Is the fraction of incident solar radiation entering the home through the windows. The lower the number, the better the window is at preventing solar gain -- critical at reducing summer cooling costs. |
|
| Cooling Index |
|
Is the Visible Light Transmittance divided by the Shading Coefficient. It relates to the ability of glass to let light in but keep solar heat out, which helps reduce energy costs for both air conditioning and lighting. The greater the number, the better.
|
|
| Visible Light Transmission |
|
In the visible spectrum, (380 to 720 nanometers), the percentage of light that is transmitted through the glazing relative to the C.I.E. ( International Commission on Illumination ) standard observer.
|
|
| Ultraviolet Light Transmission |
|
The amount of ultraviolet light allowed to penetrate the glazing.
|
|
| Relative Heat Gain |
The total amount of heat gain through a glazing system at NFRC/ASHRAE specified summer conditions, incorporating the U-Value and the Solar Heat Gain Coefficient. The conditions are 230 Btu/hr/ft2 , outdoor temperature of 89 degrees F, and 7.5 mph wind. Expressed in terms of Btu/hr/ft2.
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