Solar Heat Gain Coefficient is the portion of directly transmitted and absorbed solar energy that enters through an architectural fenestration product.

It tells you how well the product blocks heat caused by sunlight. The lower a window’s solar heat gain coefficient, the less solar heat it transmits, and the greater its shading ability. It may be expressed in terms of the glass alone or may refer to the entire window assembly.

Units and Measures

It is a unitless measure. A simple way to explain solar heat gain coefficient is in terms of a ratio; where 1 is the maximum amount of solar heat gain that can come through a window and 0 is the least amount. A Solar Heat Gain Coefficient of 0.40 means that 40% of the available solar heat is coming through the window.

The most common angle of incidence is normal to the specimen while measuring solar heat gain coefficient. However, it is possible to test at any angle of incidence or with fixed specimen.


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