Evaluating Glare in Leed Certified Buildings to Inform Criteria for Daylighting Credits

Abstract

Extensive documentation has been developed to support the benefits of daylight for building occupants. Recently, the high performance building industry has shown a trend towards prioritizing better daylighting conditions. In response to this trend, the Leadership in Energy and Environmental Design (LEED) rating system now addresses daylighting and views as one of the criteria for compliance. However, effective daylighting has its challenges—most importantly addressing the issue of glare. This paper discusses the issue of glare and its relationship with requirements for effective daylighting within the criteria of the LEED rating system. In this study, a LEED certified building on Montana State University's campus was considered as a case study. This paper conducts an analysis by comparing the results obtained from compliance procedures for LEED with independent evaluations of glare using simulation and post occupancy evaluation surveys. This paper concludes that the ‘illuminance simulation’ option provided in the current version of LEED (LEED v4) for compliance does not adequately address the issue of glare. This paper provides recommendations to improve the LEED rating system for indoor environmental quality which include: the incorporation of glare assessment in the evaluation procedures of daylighting and views; the use of dynamic simulations that incorporate climatic conditions in the evaluation of daylighting; and evaluating glare in early stages of design by using simulation tools.

Daylighting Performance Simulation: Prediction Accuracy/Processing Speed Trade-Off

“…The daylight glare probability (DGP) was selected as the indicator for discomfort glare analysis [54,55]. DGP classifies the probability of glare under four categories:…”

Biomimicry as an Approach to Improve Daylighting Performance in Office Buildings in Assiut City, Egypt

“…The annual average lux values for the four main façades in a typical office building in Assiut City (namely, the northern, eastern, southern, and western facades), are 1662, 4714, 5747, 5021 lux, respectively. The southern facade has the highest average annual illumination value of 5747 lux, therefore, the highest glare and visual discomfort possibilities [3,33]. The WWR as well as the use of a proper shading system/s strongly affect the daylighting performance; and therefore, the glare level and visual discomfort [29,34].…”

“…Acceptable Annual Average Lux (AAl) range is assumed, according to the Daylight Availability and Useful Daylight Illuminance (UDI), to be between 300 lux and 3000 lux; satisfying LEED v4.1 requirements [3,33,49].…”

“…DGP index, developed by Wienold and Christofferen, measures the possible visual discomfort in the scene, being categorized into four levels of probability that a person would experience (i.e., imperceptible (DGP ≤ 34 %), perceptible (34 % < DGP ≤ 38 %), disturbing (38% < DGP ≤ 45 %) and intolerable glare (DGP> 45 %) [28,47]). ClimateStudio performs annual hourly glare simulations by sDG which is based on Daylight Glare Probability (DGP) [33]. sDG is the percentage of views, across the regularly occupied floor area, that experiences Disturbing or Intolerable Glare (DGP > 38%) for at least 5% of occupied hours [50].…”

“…AAl range is assumed to be between 300 lux and 3000 lux. sDG must achieve the lowest possible percentage [3,33,49,45].…”