Evaluation of Directional Shading Fabric Composites with Application to Improved Daylighting

Abstract

This paper documents research toward the development of an advanced, prototype shade fabric composite designed to improve daylighting and control solar heat gain. The textiles and directional elements used reflect a portion of the incoming, broadband-average, solar radiation while redirecting light up to the ceiling, thus reducing glare and the amount of artificial light needed. An apparatus was built to measure the biconical transmittance distribution of beam radiation to test the performance of designs under consideration. Initially, based on directional elements that included clear acrylic plastic rods and fiber optic cables, we qualitatively evaluated conceptual designs* that incorporate the refraction and diffusion characteristics of the acrylic plastic rods, combined with a reflective element to redirect light upwards. Then, using a miniblind as a model, we explored a fabric design with a Z-pleat cross section and a variable-pitch reflecting tape attached to a fabric substrate. We measured the biconical transmittance distributions of several configurations to evaluate various fiber cross sections and pleat aspect ratios. This led to a composite with a round fiber cross section, an aspect ratio of 1.5 to 1, and a specular reflecting tape. The exploratory design was refined by determining the effects on the transmittance distribution of variations in pleat scale, reflecting tape tilt angle, and shade orientation. The resulting prototype design allows occupants to trade-off daylighting enhancement against shading performance, depending on time of day, season, and window orientation.