Standard daylight coefficient model for dynamic daylighting simulations

Daylight coefficients are normalized contributions from discretized sky or ground segments, or preset solar positions, to solar quantities calculated at various building sensor points. Once generated, daylight coefficients can be folded against luminance efficacy and distribution models to calculate, for instance, time series of illuminances. Over about the last 25 years several daylight coefficient models have been published. The objective of this paper is to propose a standard daylight coefficient model for dynamic daylighting simulations (DDS), consolidating previously published methods. This entails the definition of a standard daylight coefficient data format and accompanying software concepts for dynamic simulation purposes; dynamic in this context meaning variable with time due to changing sky conditions and shading device settings, in contrast to static modelling concepts such as daylight factors. The DDS standard model defines daylight coefficient data independent of building location and scene orientation, and generated using either simulation or measurement. It provides functionality to take into account independently controlled daylighting sources (e.g. windows and skylights) and to query different daylighting quantities in a simulation context (e.g. illuminance at one or more sensors, annual daylight performance metrics). A Radiance-based intermodel comparison shows that DDS-based software outperforms the original validated Daysim approach, upon which DDS is based, notably in cases where sensors are subjected to sudden changes in solar exposure, e.g. in an urban canyon or for sensors located far from a window. The proposed DDS standard daylight coefficient model, including the data format and accompanying software concepts, can be adopted by daylighting and energy-simulation software as a common mechanism for efficiently sharing daylight coefficient data for simulation purposes.