The shading coefficient (SC) is a single-number indicator used to characterise the solar radiant heat gain through fenestrations used in buildings. The shading coefficient is defined in terms of the solar heat gain factor (SHGF), the fraction of incident solar irradiance that is transmitted into the room as heat. The SC is the ratio of the SHGF of the fenestration in question to that of a standard reference glazing under specified standard conditions. The standard conditions include normal incidence and no interior shading. This paper develops an expression for modifying the shading coefficient to include the effects of interior shading when the shade is a simple, freestanding vertical sheet. It is shown that such interior shading can strongly affect the shading coefficient of the window/window shade combination.

KEYWORDS: indoor, shades, windows, solar radiation, models, solar heat gain, comparing, glazing.