G-VALUE

When discussing the properties of fenestration (e.g. windows and patio doors) and shading devices, the 'G-value' is a commonly mentioned property. It is the sum of the primary transmittance (T-value) and the secondary transmittance. The secondary transmittance is the ratio of the inwardly flowing fraction of the solar energy absorbed in the window (or shading device) to the solar insolation.
In North America, the g-value is called the Solar Heat Gain Coefficient (SHGC).
The T-value is the primary energy transmittance. It is the ratio of the transmitted insolation through the window (or shading device) to the solar insolation.
The difference between the g-value and the T-value is the percentage of the solar insolation which is absorbed in the window (or shading device) which reaches the room through heat transport.

Contents

G value - The number of molecules produced or destroyed for each 100 eV spended on ionization or irradiation of substance.