Determining Off-Normal Solar Optical Properties of Roller Blinds

Abstract

Solar gain through fenestration constitutes a significant portion of peak cooling load and annual energy consumption in buildings. As such, any reduction in solar gain translates into savings associated with the cost of purchasing and operating cooling equipment. Shading devices in general, and roller blinds in particular, can be used to reduce solar gain appreciably. The performance of a roller blind is largely determined by its solar optical properties. In this study, an integrating sphere was used to obtain off-normal solar properties of six typical roller blind samples. Measurements were used to develop semi-empirical models for the off-normal beam-beam, beam-diffuse, and diffuse-diffuse solar optical properties. The models provide a means to calculate off-normal properties by adjusting known values of beam-beam transmittance (i.e., openness), beam-total transmittance, and beam-total reflectance measured at normal incidence. The properties that apply to normal incidence are readily obtained. Such models are valuable components of building energy simulation software.