Directional and hemispherical solar-energy transmittance of single and double glazing

摘要

Abstract: Solar and visual light transmittance, color appearance, thermal emissivity, and other optical properties of architectural glazing are in general angular dependent. Realistic computation of solar properties, therefore, requires the angular behavior to be known. Determination of these properties for normal or near-normal incidence according to the standards is part of a standard procedure for most laboratories, while experimental data on their angular behavior can, in general, only be obtained with great difficulty. An alternative way of determining angular properties is by calculation. This is possible using a model based upon Fresnel's equations and the optical constants of all optical media involved (glass and coatings). The optical constants (spectral complex refractive index) can be derived from the transmittance and reflectance spectra which are measured for normal or near-normal incidence. The paper discusses in detail both the measurement methods and the computer model for the determination of directional and hemispherical solar energy transmittance of single and double glazing. Results are given for single and double glazing with and without spectrally selective coating (SnO$-2$/). !10