Achieving daylighting credits for LEED
Creating the simulation and analysis
Simulation details include several items:
- The building is located in Northwest Chicago, Illinois. By closest approximation, the daylight model was located at a latitude 42 deg north and longitude 88 deg west.
- All of the assessment results in this study were conducted on an analysis plane positioned 30 in. above each finished floor. The date and times for the simulation were set on Sept. 21 (fall equinox) at 9 a.m. and 3 p.m.
- The luminance sky distribution set in AGi32 lighting simulation software was clear sky.
Surface properties: The visible light reflecting properties of the internal surface finishes and transmission properties of the glazing for the individual spaces were assigned according to the surface finish and glazing schedule provided by architects (see Table 1).
Space classification: The following are selected as regularly occupied areas (as defined by USGBC) because they are spaces where one or more individuals normally spend time (more than 1 hour per person per day on average) seated or standing as they work, study, or perform other focused activities inside a building.
Daylighting analysis, including:
- Building spaces: The combined floor area of the regularly occupied spaces in the building is approximately 1462 sq ft. Most of the regularly occupied offices in the building mainly face south or east. They receive direct daylight during the evaluation time and therefore have the highest daylight levels of the offices in the building.
- Iso-contour plan and calculation summary (see Figure 1).
Achieving the goal
The daylight levels for all regularly occupied spaces were assessed individually for Sept. 21 at 9 a.m. and 3 p.m. using architectural drawings and schedules for the opaque surface finishes and glazing. The sun position and sky distribution required for analyzing the probability of achieving LEED daylight and views credit is a good criterion for evaluating the overall daylighting performance because the sun is at low angles and it is a mid-season sun.
The daylighting performance of the prototype building is balanced with even daylight distribution. All the spaces analyzed were comprised of relatively small floor areas. In this example, the daylight analysis results show the building has 85% of the regularly occupied space floor area of 25 to 500 fc at 9 a.m. and 75% at 3 p.m. Because this result meets the minimum requirement for the LEED EQc8.1: Daylight and Views - Daylighting credit, the proposed design is anticipated to achieve 1 point for this credit.
Siva Haran is a senior electrical engineer and project manager at exp. He is an advisory member of Sustainable Lighting Committee of IES. He has extensive experience in designing lighting and electrical systems for commercial, institutional, light industrial, and residential projects.
See tips for analyzing daylighting, as well as a glossary/definitions below.