Evaluation of view clarity through solar shading fabrics

Abstract

There is extensive literature showing the effect of solar shading devices on energy savings, preventing overheating and achieving occupants’ visual comfort in highly glazed office spaces. Nevertheless, solar protection devices can also significantly diminish the visual contact with the outside. This work evaluates the view to the outside through exterior solar shading fabrics and provides new data for development of a revised View Clarity Index. 50 subjects evaluated their view to the outside through nine fabrics of different colors and openness factors (OF) mounted on windows of identical test cells. In parallel, interior and exterior vertical and horizontal illuminances were monitored along with fabric luminance during each experiment. It was observed that the view to the outside was highly influenced by the fabric OF and color. The higher the OF and the darker the fabric, the clearer the view to the outside. However, their combined effect is quite complex. Interestingly, view clarity through the dark-colored fabric with OF=3% was estimated better than that of the light-colored fabrics with OF=10%. Based on the new data, a revised formula for the View Clarity Index (VCI) is proposed for predicting view clarity through fabrics, based on the normal-normal and normal-diffuse light transmittance factors of the material. Finally, the new findings show that the current performance classification scheme of the European standard EN 14501 needs further refinement. New classes are proposed as valuable information towards accurate assessment of outside view through fabrics in future revisions of the standard.