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Evaluating daylighting effectiveness and occupant visual comfort in a side-lit open-plan office building in San Francisco, California

Abstract

The introduction of daylight to reduce electrical lighting energy consumption and to enhance Indoor Environmental Quality is one of the most common claims made for commercial office buildings promoted as “sustainable,” “energy efficient,” “green,” or “high performance.”  However, daylit buildings are rarely studied in use to examine the impact of design strategies on visual comfort, or to examine how occupant modifications to the facade may reduce daylighting effectiveness and visual connection to the outdoors.   This paper presents key findings from a post-occupancy study of a side-lit open-plan office building located in San Francisco, California.  The study examines daylighting performance over daily and seasonal changes in sun and sky conditions in core and perimeter zones of the building.  Daylighting performance is assessed through measurements of electrical lighting energy, observations of occupant modifications to the facade, and physical measurements of interior lighting conditions paired with occupant subjective assessments using novel desktop polling station devices.  Results show a high frequency of visual discomfort responses at both perimeter and core workspaces and observations reveal a large percentage of facade glazing covered by interior shading devices.   Despite the significant reduction in effective visible light transmission, occupants working in the perimeter zones generally considered the levels of available daylight to be sufficient, even when daylight levels were below recommended thresholds for daylight autonomy.  Issues related to the daylighting design strategies are discussed in regard to improving the performance of future daylit buildings and refining daylighting design criteria.

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