Estimation of Solar Optical Properties for Windows

Abstract

To calculate dynamic solar heat gain in buildings, one must know solar optical properties, namely, incidence-angle-dependent solar-transmittance, absorptance and hence -reflectance of window systems. The properties may be estimated using procedures which use Fresnel equations and ray-tracing technique or matrix multiplication method. This paper presents a simple generalized procedure to estimate incidence-angle-dependent solar optical properties of clear, tinted and coated glass of any thickness. Knowing the solar optical property of a glass at normal incidence, incidence-angle-dependent solar optical property may be estimated from corresponding relative solar optical property. The estimated results for different window systems are compared with measured values of incidence-angle-dependent solar-transmittance and—absorptance and are discussed. It is observed that the calculated results are quite close to the corresponding measured ones (with maximum relative error of 11.18%) up to 70° incidence angle for various types of glazings considered. However, this relative error increases beyond this angle up to 80° and then starts decreasing.