Solar Heat Gain Coefficient

Solar gain (also known as solar heat gain or passive solar gain) refers to the increase in temperature (heat gain) in a space, object or structure that results from solar radiation. The amount of solar gain increases with the strength of the sunlight, and with the ability of any intervening material to transmit or resist the radiation.

Objects struck by sunlight absorb the short-wave radiation from the light and reradiate the heat at longer infrared wavelengths. Certain materials and substances, such as glass, are more transparent to the shorter wavelengths than the longer; when the sun shines through such materials, the net result is an increase in temperature — solar gain. This effect, the greenhouse effect, so called due to the solar gain that is experienced behind the glass of a greenhouse, has since become well known in the context of global warming.

When discussing the properties of windows, doors and shading devices, shading coefficients are commonly mentioned properties. Shading coefficients measure the solar energy transmittance through windows.

for all practical purposes especially in countries like India or rather within Asian zone where there is ample of sunlight & heat available, it is better to optimise solar factor i.e. to orient your glass with high solar factor such that you allow maximum sunlight to enter the interior of the structure.Hence if used in offices there is absolute no electricity consumption of artificial lights during day time and since they may be offices with huge working area which are closed during night time, the structure can count of light efficiency achievement of 100% with reducing the energy consumption of the structure accodingly.however for all south zone countries it is recommended not to exceed this value by 0.4 or 40%

g-values and SHGC values ranges from 0 to 1, a lower value representing less solar gain. Shading coefficient values are calculated using the sum of the primary solar transmittance (T-value) and the secondary transmittance. Primary transmittance is the fraction of solar radiation that directly enters a building through a window compared to the total solar insolation, the amount of radiation that the window receives. The secondary transmittance is the fraction of inwardly flowing solar energy absorbed in the window (or shading device) again compared to the total solar insolation.

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Wikipedia