Solar shading of windows: A simple photographic analysis

Solar gains through windows provide an important contribution to the space heating of a house. However, nearby obstructions may produce considerable shading. This is likely to be greatest in winter when the sun is low in the sky, but when the heat is most needed. This note describes a technique for the measurement of solar shading in existing houses. Photographs are taken out of each window, using a camera fitted with a wide angle lens. The camera must be level, and the compass bearing of a prominent reference point noted. Sun path diagrams may then be sketched on the photographic prints, using a programmable calculator to calculate solar positions. In this way, times of appearance and disappearance of the sun can be very rapidly estimated, and compared with the maximum possible sunshine duration that would exist in the absence of any obstructions. The advantage of this method compared with existing techniques is that it requires the very minimum of special equipment: a wide angle camera fitted with a spirit level, and a hand bearing compass. The camera may be used without a tripod, making it convenient for rapid surveys in occupied houses. A simple mount is described, which may be used with a compact 35 mm camera.