Determining Off-Normal Solar Optical Properties of Drapery Fabrics

Abstract

The determination of off-normal solar optical properties of drapery fabrics is particularly useful in modelling the effective solar optical properties of pleated drapery. Special sample holders were designed and fabricated to facilitate measurements using an integrating sphere installed in a commercially available spectrophotometer. Measurements were taken for eight of the nine fabric designations documented in the ASHRAE Handbook – Fundamentals. Measurements were also obtained for a sheer fabric which does not fall into any of the customary fabric designations. Semi-empirical models were developed to quantify the variation of solar optical properties with respect to incidence angle. Given solar optical properties obtained at normal incidence, these models can be used to characterize the off-normal beam-beam and beam-diffuse properties of a drapery fabric. The fabric models comprise a useful component of pleated drapery models and, in turn, a valuable tool for building energy simulation. The measurement technique described in this study can be used to obtain the off-normal solar optical properties of additional flat shading devices such as roller blinds and insect screens.