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European U-Value (formerly K-Value) Based on ISO-DP10292 draft standard conditions. It is based on an outdoor temperature of 5.5°C, and indoor temperature of 20.5°C and a 4.8 m/s outdoor air velocity
Light to Solar Gain Ratio (LSG)The ratio is equal to the Visible Light Transmittance divided by the Solar Heat Gain Coefficient. The Department of Energy's Federal Technology Alert publication of the Federal Energy Management Program (FEMP) views and LSG of 1.25 or greater to be Green Glazing/Spectrally Selective Glazing
R-ValueThermal resistance is expressed in ft^2/hr/°F/BTU. It is the reciprocal of U-value. The higher the R-value, the less heat is transmitted through the glazing material.
Relative Heat Gain (RHG)The amount of heat gained through glass taking into consideration the effects U-value and shading coefficient. Using the NFRC standard, relative heat gain is calculated as follows: English System: RHG = (Summer U-value x 14°F) + (Shading Coefficient x 200). Metric System: RHG = (Summer U-value x 7.8°C) + (Shading Coefficient x 630). The lower the RHG, the more the glass product restricts heat gain.
Shading CoefficientShading coefficient is the ratio of solar heat gain through a specific type of glass that is relative to the solar heat gain through a 1/8" (3mm) ply of clear glass under identical conditions. As the shading coefficient number decreases, heat gain is reduced, which means a better performing product.
Solar Heat Gain Coefficient (SHGC)The portion of directly transmitted and absorbed solar energy that enters into the building's interior. The higher the SHGC, the higher the heat gain.
Solar ReflectanceThe percentage of solar energy that is reflected from the glass surface(s)
Solar TransmittanceThe percentage of ultraviolet, visible and near infrared energy (300 - 3000 nanometers) that is transmitted through the glass
U-ValueA measure of heat gain or heat loss through glass due to the differences between indoor and outdoor temperatures. These are center pane values based on NFRC standard winter nighttime and summer daytime conditions. U-values are given in BTU/hr/ft^2/°F for the English system. Metric U-values are given in W/m^2/°C. NFRC winter nighttime U-values are based on an outdoor temperature of 0°F (-17.8°C), an indoor temperature of 70°F (21°C) and a 12.3 mph (19.8 km/h) outdoor air velocity. NFRC summer daytime U-values are based on an outdoor temperature of 89°F (32°C), an indoor temperature of 75°F (24°C), a 6.2 mph (10.1 km/h) outdoor air velocity and a solar intensity of 248 BTU/hr/ft^2/°F (782 W/m^2).
Ultraviolet Light (UV)The name of the invisible portion of the light spectrum with wavelengths shorter than 390 nanometers. The damaging effects on long-term UV exposure results in fabric fading and plastic deterioration.
Visible Light ReflectanceThe percentage of light that is reflected from the glass surface(s)
Visible Light TransmittanceThe percentage of visible light (380 - 780 nanometers) that is transmitted through the glass. (Visible light is the only portion of the solar spectrum visible to the human eye.)
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