New Tools for the Evaluation of Daylighting Strategies and Technologies

The use of daylight for the illumination of building interiors has the potential to enhance the quality of the environment while providing opportunities to save energy by replacing or supplementing electric lighting. Moreover, it has the potential to reduce heating and cooling loads, which offer additional energy saving opportunities as well as reductions in HVAC equipment sizing and cost. All of these benefits, however, assume "proper" use of daylighting strategies and technologies, whose performance depends on the context of their application. On the other hand, "improper" use can have significant negative effects on both comfort and energy requirements, such as increased glare and cooling loads. To ensure proper use, designers need tools that model the dynamic nature of daylight and accurately predict performance with respect to all performance aspects affected, which extend beyond comfort and energy to include esthetics, cost, security, safety, etc.

Research and development efforts during the last twenty-five years have resulted in a number of computer-based tools, with varying degrees of modeling capabilities and prediction accuracy. Most of these tools, however, especially those with extended modeling capabilities and high degree of accuracy, are very expensive to use. In addition to extensive training, they require time-consuming preparation of input that describes the building and its context, and significant processing of the output to evaluate and analyze the predicted performance. In this paper, we present two software tools that will eventually contribute to faster and better evaluation of daylighting strategies and technologies.

The first tool is the Building Design Advisor (BDA), which facilitates the use of multiple simulation tools by automating the preparation of the required input and integrating the output in graphic displays that support multi-criterion, simultaneous evaluation of multiple design options. Through a "smart" default value mechanism, it allows use of simulation tools from the early, schematic phases of building design. Moreover, through links to a Web-based case studies database of actual buildings, it facilitates formulation of realistic performance targets and evaluation of alternative design schemes. The 1.0 version of the BDA is linked to two simplified simulation tools, one for the prediction of daylight work-plane illuminance and glare index in rectangular spaces, and the other for the prediction of energy requirements by end use and energy source, which also includes HVAC auto-sizing.

The second tool is the latest release of the RADIANCE day/lighting simulation and rendering program, which computes luminance and illuminance values for arbitrary space and fenestration configurations. In addition, RADIANCE produces photo-accurate images of the modeled environment. The added functionality in the new release supports post-processing of the computed images to make them closely correspond to the dynamic exposure and tone mapping of the human eye. It also supports the generation of animated walk-through and time sequences.

Our plans for the future include the development of links between a PC version of RADIANCE and the BDA. With the BDA also being linked to the DOE-2 building energy simulation program, we expect to integrate the use of simplified and sophisticated tools to address daylighting from the early, schematic phases of building design through the detailed specifications of building components and systems.