The sensitivity of modern high-performance glazing systems to both the angle of incidence and the shape of the incident solar spectrum is examined using a glazing performance simulation program. It is found that as the spectral selectivity of the glazing system increases, the solar heat gain coefficient can vary as the incident spectral distribution varies. The variations can be as great as 50% when using several representative direct-beam spectra. These include spectra having low and high air masses and a standard spectrum having an air mass of 1.5. The variations can be greater if clear blue diffuse skylight is considered. It is recommended that the current broad-band shading coefficient method of calculating solar gain be replaced by one that is spectral based.

KEYWORDS: year 1996, spectra, windows, glazing, solar heat gain, calculating, solar radiation, solar control films, accuracy