- SOME COMBINATIONS OR INSTALLATIONS MAY REQUIRE HEAT
TREATING TO PREVENT GLASS BREAKAGE FROM THERMAL STRESS
- Visible, Total Solar and UV data are based
on laboratory spectrophotometric measurements weighted by an appropriate
weighting function(s) using LBNL Window 5.2 software. The wavelength
ranges of the sun’s energy used to calculate properties:
Visible from 0.38 to 0.78 microns, Total Solar from 0.30 to 2.5
microns and UV from 0.30 to 0.38 microns.
- Transmittance- Percentage of normally incident
visible light or solar energy passing directly through the glazing.
- Reflectance- Percentage of normally incident
visible light or solar energy reflected away from the glazing.
- U-Value- (Btu/hr/sq-ft/degrees Fahrenheit)
- Measure of the heat gain or loss through glazing due to environmental
differences between the outdoor and indoor air. U-Values given
are center-of-glass values calculated using LBNL window 5.2. Winter
U-Values are based on an outdoor temperature of -0.4 degrees Fahrenheit
(-18 degrees Celsius), an indoor temperature of 69.8 degrees Fahrenheit
(21 degrees Celsius) and a 12.3 mph (5.5m/s) wind velocity with
no sun. Summer U-Values are based on an outdoor temperature of
89.6 degrees Fahrenheit (32 degrees Celsius), an indoor temperature
of 75.2 degrees Fahrenheit (24 degrees Celsius), a solar intensity
of 248.2 Btu/hr/sq-ft (783 W/sq-m) and a 6.3 mph (2.8 m/s) wind.
To obtain metric U-Value (W/sq-m/degrees Celsius), multiply by
5.678.
- Solar Heat Gain Coefficient or SHGC- The ratio
of the total solar heat gain through the glass relative to the
incident solar radiation. The solar heat gain includes both the
solar energy directly transmitted through the glass, plus the
solar energy absorbed by the glass and subsequently convected
and thermally radiated inward.
- Shading Coefficient or SC- The ratio of solar
heat gain through the glass relative to that through 1/8"
(3mm) clear glass at normal incidence. Note that Relative Heat
Gain or RHG (Btu/hr/sq-ft), which is the amount of heat gained
through the glass at assumed conditions, can be calculated using
the following equation: RGH = SC(200) + U-Value (14). To obtain
metric RHG (W/sq-m), multiply by 3.154.
- Sound Transmission Class or STC- A single number
rating derived from individual transmission losses at specified
test frequencies in accordance with ASTM E90 and ASTM E413.
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