Experimental and simulation analysis of daylight glare probability in offices with dynamic window shades

Publication date: May 2015
Source:Building and Environment, Volume 87
Author(s): Iason Konstantzos , Athanasios Tzempelikos , Ying-Chieh Chan
This paper presents an experimental and simulation study to evaluate daylight glare probability (DGP) in office spaces with roller shades. Roller shades can be controlled in various ways and have an openness, transmitting direct and diffuse light even when fully closed. Since DGP combines the overall brightness of the visual field and the perceived contrast of the scene in one metric, the development of glare protection guidelines is complex in this case. Full-scale experiments with an HDR camera in test offices were combined with a validated, integrated daylighting and glare model. Correlations between DGP and design parameters (work plane or vertical illuminance) were developed and the applicability of DGP and DGPs for closed and controlled shades is discussed. The results show that DGPs is not an accurate metric when the sun is within the field of view – even for low openness fabrics – while the DGP equation might need a correction for such cases, due to extreme values of the solar corona's luminance influencing the luminance term. DGP and work plane illuminance are not well correlated, except for the case of perfectly diffuse fabrics. However, for all instances when the sun is not visible by the occupant, DGPs can be used to approximate daylight glare, including cases with sunlight on various surfaces in the space, for any fabric openness and control type. This enables the development of model-based, real-time glare control shading operation, with vertical illuminance being the basic parameter. Simple sunlight protection strategies cannot prevent glare, despite maximizing daylight utilization.