The solar radiation transmitted into a living space is less than the radiation that strikes the outside of a window because of losses associated with radiation reflected off of and absorbed by the glass. The manual presents data for windows with conventional, single-strength clear double glazing and a glass thickness of 0.125 in. Tables contain values for unshaded and shaded windows. Unshaded values are for windows with no external shading. Shaded values are for windows with no external shading.
Shaded values are for windows shaded by a roof overhang.
The roof overhang and window geometry are shown at the top of each data page. The overhang width and the vertical distance from the window to the overhang are given in dimensionless units for a window height of 1.0. For south-facing windows, the geometry balances the need for maximum heat gain during the heating season without creating unreasonable heat gain during the cooling season. The same shading geometry is used for all vertical windows for a station. As described in the Appendix, the shading geometry is generally a function of the station latitude but consideration is also given to heating and cooling requirements.