Calculating the Solar Heat Gain of Window Frames

Abstract

It is not practical to measure the solar heat gain of a window frame. It is more practical to do so by calculation. Typically, the frame solar heat gain is a small component of the total or is small in absolute terms so an approximate method is satisfactory. A simple approach for calculating the solar heat gain coefficient of any opaque window component is developed. The parameters appearing in the expression clearly identify the mechanisms of frame solar gain and indicate the ways in which it can be controlled. A particularly simple expression can be applied to any frame geometry for cases in which the solar radiation is incident normal to the window. This is especially useful because this condition is frequently used for energy rating purposes, code compliance, and design. It is shown that this expression is also valid for off-normal incidence as long as no part of the frame is shaded. An adjustment, based only on frame surface geometry, can be applied if the frame is partially shaded. Sample calculations closely reproduce the results of detailed two-dimensional numerical simulation.