Benchmark of methods for annual glare risk assessment

Abstract

Visual comfort in buildings has a critical impact on occupants' health and mental performance. Among the visual comfort functions, daylighting glare is the most complex phenomenon to assess by architects and practitioners. This paper aims to benchmark state-of-the-art methods for annual glare analysis and develop strategies to reduce the computational time (CPU time) without compromising the accuracy of glare calculations. The Radiance-based tool rtrace and the Radiance-based five-phase method (5pm) are applied to a single room. Analytical isotropic fabric systems are parametrized in terms of specular/diffuse scattering components and cut-off angle. Peak extraction considered by Radiance's aBSDF material primitive is key to having an accurate representation of the luminance maps and vertical illuminance at eye level and glare calculations. A minimum number of ambient bounces (ab parameter) of 4 when using Radiance's rtrace program achieves the best trade-off between accuracy in vertical illuminance and daylight glare probability (DGP), and CPU time. Based on semi-annual and five days per week simulations for visible sun positions, sampling strategies can decrease the CPU time for annual glare simulations up to 86% when considering clear sky conditions. The most suitable method for DGP simulations depends strongly on the Radiance parameters and the chosen sampling strategy.