Directional anisotropy of diffuse solar irradiance: impact assessment on the solar transmittance of common glazings.

Abstract

The solar transmittance of transparent glazings is a key factor in determining the solar gain and thermal balance of a building. The transmittance calculation must be made separately for the beam and diffuse components of the incident solar irradiance. Most simulation software uses an isotropic distribution for diffuse irradiance, approximation that can be inaccurate under clear or partially cloudy skies. An anisotropic distribution of diffuse irradiance is implemented in this work, its diffuse transmittance is evaluated for real sky conditions and compare against experimental data. The results show that the anisotropic model does not offer significant advantages over the isotropic one.