Solar factor and shading coefficient

What is the difference between solar factor and shading coefficient?

The solar factor, often simply referred to as the ‘g value’, is the percent of solar energy incident on the glass that is transferred indoors both directly and indirectly through the glass. The direct gain portion is the solar energy transmittance, while the indirect is the fraction of solar energy incident on the glass that is absorbed and re-radiated or transmitted through convection indoors. For example, 3 mm uncoated clear glass has solar factor of approximately 0.87, of which 0.85 is direct gain (solar transmittance) and 0.02 is indirect gain (convection / re-radiation).

The Shading Coefficient (SC) is a measure of the heat gain through glass from solar radiation. Specifically, the Shading Coefficient is the ratio between the solar factor or a particular type of glass versus a 3 mm float glass with a g value of 0.87. A lower Shading Coefficient indicates lower solar factor. For reference, 3 mm clear glass has a value of 1.00.

In either case, a lower number indicates reduced levels of solar gain. For buildings with the potential to have a long air-conditioning season, it is most important to reduce solar gain and therefore reduce air-conditioning loads. In Europe, solar factor & shading coefficient are both calculated in accordance with EN 410.