Paper Conference

Proceedings of SimBuild Conference 2010: 4th conference of IBPSA-USA


Dynamic Radiance: Predicting Annual Daylighting with Variable Fenestration Optics Using BSDFs

Mudit Saxena, Greg Ward, Timothy Perry, Lisa Heschong, Randall Higa
Heschong Mahone Group, Gold River, CA
Anyhere Software, Albany, CA
Southern California Edison, Irwindale, CA

Abstract: Existing annual daylight simulation software fall short with respect to variable fenestration optics that change interior daylight distribution with sun position and/or operating schedule, thus limiting the ability to compare the performance of advanced fenestration systems. Many of these window or skylight systems can be described efficiently as a bidirectional scattering distribution function (BSDF), which characterizes their flux output as a function of input for a particular configuration. In this paper, we describe a new method that employs measured or simulated BSDFs to permit fast, matrix-based annual daylighting calculations. The matrices themselves are precomputed by Monte Carlo ray-tracing in a modified daylight coefficient approach we call Dynamic Radiance. The inner time-step loop then consists of multiplying the desired sky luminance vectors against three matrices in the general case, where a separate BSDF matrix permits dynamic fenestration control strategies. In this paper, the authors describe their implementation of the Dynamic Radiance method and demonstrate its application to a set of 61 real spaces modeled for a research project to determine new daylight metrics. We present results from these simulations and discuss advantages and limitations of the new approach.
Pages: 402 - 409