What is a shading coefficient?


Quick Answer

The shading coefficient is a number derived by comparing total solar heat transmittance of glazed windows to that of clear glass having a total solar heat transmittance of 0.87. Lower shading coefficients mean windows allow less heat into buildings through direct sunlight, whereas higher shading coefficients mean more heat is present. Heat coefficients go from zero to one, with one being 100 percent transmission of the sun's heat through glass.

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Full Answer

Solar heat gain coefficients are other ways to measure how much heat windows absorb into structures. Solar heat gain coefficients have similar numbers to shading coefficients, except the number takes into account the fraction of solar radiation that enters a building through the entire window assembly. To convert the shading coefficient to solar heat gain, multiply the shading coefficient by 0.87.

A coefficient more than 0.8, or 80 percent, is typical for uncoated window panes. The darkest tinted windows often have shading coefficients of 0.2, or 20 percent. Other coefficients and percentages used for windows include solar transmittance, solar reflectance, visible light transmittance, total solar energy reflected and solar heat reduction.

Tinted windows and low-E coatings reduce the solar heat gain coefficient. Tints come in shades that include black, gray, blue, bronze, brown, gold and silver.

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