A systematic method for selecting roller shade properties for glare protection

Currently, there is no methodical procedure for selecting solar-optical properties of roller shades, which affect the energy and indoor environmental performance of perimeter building zones. This paper presents anew systematic methodology for identifying the range of shading properties (openness factor and visible transmittance) that can significantly reduce the risk of glare. A model-that calculates angular beam-beam and beam-diffuse shading optical properties using minimum inputs is used within a hybrid ray-tracing and radiosity daylighting model, validated with full-scale experiments. The temporal variation of beam and total vertical illuminance is used to define the annual visual discomfort frequency and establish a process for selecting the range of acceptable shading properties for each set of external parameters (location, orientation, glazing visible transmittance, and buffer zone). The combined impact of visible transmittance and openness factor on discomfort frequency and daylight metrics is non-linear and complex. Recommendations for openness factors and visible transmittance values are made for different scenarios. Selecting the upper limits of suggested ranges can provide more daylight into the space and reduce the probability of high contrast. These guidelines may be used for selection of shading products, followed by considerations about energy savings and provision of outside view. (C) 2015 Elsevier B.V. All rights reserved.