The Role of Metrics in Performance-Based Design

To evaluate the performance of buildings in use and to predict performance during design, it is necessary to identify what the appropriate measures of performance should be, when and how measures should be collected, and how results will be interpreted to determine success or failure. As noted in Chap. 1, one of the central barriers to effective daylighting is that daylighting performance is often defined differently by different stakeholders, leading to a fragmented approach to performance assessment in the design and operational life-cycle of buildings. While daylighting has most consistently been promoted as a means of electrical lighting energy reduction, greater understanding of the health benefits of daylight and views combined with greater awareness of discomfort glare and the mandate to minimize heating/cooling loads to achieve low and Zero Net Energy (ZNE) buildings has led to an expanding set of performance considerations. Existing metrics, performance criteria and methodologies for assessing daylit spaces have evolved largely from the legacy of metrics developed for the electrical lighting industry, and hold many of the same underlying assumptions. Therefore, it is import to identify and understand the strengths, weaknesses and limitations of these assumptions in assessing the dynamic qualities of daylight spaces. There are many indicators available for design teams to predict and assess the outcome of daylighting strategies, each with underlying assumptions for the lighting needs, preferences and behaviors of building occupants. This chapter presents a broad assessment of the energy and human-factors performance metrics that should be considered to achieve effectively daylit buildings. The chapter is divided into sections, each discussing a key performance objective. The chapter prioritizes discussion of metrics implemented in consensus-based green building rating systems, whole-building energy benchmarking frameworks and targets, and in softwarebased evaluation tools on the basis that these metrics are anticipated to have the greatest short-term influence on the design and evaluation of daylit buildings.