Daylighting prediction software: comparative analysis and application

Daylighting is a beneficial design strategy since it may provide energy savings and contribute to a more sustainable design. In recent studies, daylighting has also been shown to increase staff and student productivity and to decrease absenteeism. The consulting engineer is often faced with the dilemma of how to design a daylighted building. What tools are available to predict the amount of daylighting? What are the design limitations and parameters? How much time is required? How does the data compare to the “real world”? The purpose of this paper is to answer these questions and provide useful information for the design of daylighted areas with the assistance of software-based simulation. A survey was made of the available software programs for the calibrated modeling of light scattered in enclosed spaces. These software packages used algorithms based on either total radiosity (flux transfer) computations or physically accurate ray tracing. A summary of this survey along with the selection criteria used in selecting a software program are presented. “Radiance”, a reverse ray tracing method software package, was chosen for use in the simulations. An existing school was modeled with the Radiance software and predictions of daylighting contributions were compared with actual data taken at the site location. The use of daylighting also requires a highly specialized lighting system. This system incorporates the use of controllable ballasts and lighting sensors to maximize the daylighting contribution to the overall required illumination. Some design criteria for this system is also discussed