A method to evaluate glare risk from operable fenestration systems throughout a year

Abstract

Nowadays buildings are being designed with large glazed areas mainly due to aesthetics considerations but also to achieve daylit spaces. However, large glazed facades are prone to cause glare problems for building users. To mitigate this risk, it is important to predict existing glare metrics dynamically and reliably in the early stages of the design of a facade. Current evaluation methods for dynamic glare are either computationally too expensive or not suitable for operable façade systems. In this study, a new method is proposed to calculate the Daylight Glare Probability (DGP) index in a computationally efficient fashion, while allowing the fenestration system to switch states during the annual simulation. The method is based on a matrix formalism to calculate the vertical illuminance at a view position, and also on the calculation of a luminance map of the field of view solely from the direct component of the light sources. A first validation of the proposed method is presented. An office setup in Freiburg is monitored with a luminance camera for different weather conditions and different façade systems. Additionally, the calculation of the DGP index by the proposed method is compared with the calculation of the DGP by backward raytracing with high rendering parameters. The proposed method has been implemented in a building simulation program, called Fener. A case study is presented to illustrate the new possibilities offered by the Fener tool. The glare risk of three different textile roller blinds, with similar visible transmittance but different openness coefficient, is assessed.