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Open Access Publications from the University of California

Evaluation of Annual Sunlight Exposure (ASE) as a Proxy to Glare: A Field Study in a NZEB and LEED Certified Office in San Francisco

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This thesis researches visual comfort and glare conditions using a field study approach. Its goal is to evaluate to what extent the Annual Sunlight Exposure (ASE) metric reflects visual comfort, as assessed from both qualitative and quantitative data collected in a NZEB and LEED Platinum certified office building. Results suggest that ASE does not adequately represent human experience and visual comfort through the illuminance plan view approach, and that future versions of this metric should use an integrated approach with luminance metrics for more accurate visual comfort and glare analysis. Ultimately, this study recommends further validation of the IES LM-83-12 and LEED v4 simulation requirements to increase confidence on the use of the ASE metric. The annual-climate-based daylighting metrics released by the Illuminating Engineering Society in 2012 and adopted by LEED in 2014 made a relevant advancement by introducing Spatial Daylight Autonomy (sDA) and Annual Sunlight Exposure (ASE) to predict daylight sufficiency and probability of glare, respectively. These new metrics address dynamic and temporal aspects of daylight not previously covered by other standards. However, the introduction of these metrics is still very recent, and current literature indicates an impending need for further refinement. To study these challenges, three objectives were delimited for this thesis: 1) Determine if ASE is a good proxy for visual comfort and glare in a field study of an existing high performance office space; 2) Categorize the daylighting performance and visual comfort in this same office space using a combination of occupant surveys and physical measurements; and, 3) Identify through a compilation of interviews with daylighting practitioners the challenges and benefits faced when applying these new metrics.In summary, this thesis examined the ASE metric and simulation requirements adopted by LEED v4 with comparative analysis involving occupant surveys, field measurements and simulation methods. While point-in-time glare and DGP analysis presented results in line with the occupant responses, ASE provided discrepant numbers in relation to annual DGP results. The conclusions indicate that ASE over-predicts glare occurrence due to unconfirmed thresholds definitions and simulation requirement limitations. Thus, this study suggests the review and fine-tuning of the ASE metric and simulation requirements for future LEED versions.

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