02440nas a2200157   4500008003900000245011900039210006900158520181800227653005202045653003202097653001602129653002502145100001902170700002102189856007202210       2013                          d00aAnnual daylighting performance of a passive optical light shelf in sidelit perimeter zones of commercial buildings0 aAnnual daylighting performance of a passive optical light shelf 3 a<p>Sunlight redirecting systems have the potential to significantly offset electric lighting energy use in deep perimeter zones of buildings where the windows are subject to high daylight availability. New Radiance modeling tools have recently been developed and validated, enabling accurate and timely simulation analysis of the annual energy and comfort performance of these optically-complex, anisotropic systems. A parametric study was conducted using these tools to evaluate the performance of a commercially-available passive optical light shelf (OLS) in a 17.4 m deep (57 ft), south-facing open plan office zone in three climates. Daylighting efficiency, discomfort glare, and lighting energy savings with continuous dimming and bi-level switching controls were determined at varying depths within the zone. The OLS decreased lighting energy use significantly throughout the depth of the space and achieved these savings with minimal discomfort glare in the area near the window. Annual lighting energy use intensity was reduced to 1.71-1.82 kWh/ft<sup>2</sup>-yr (22-27%) over the full depth of the perimeter zone across the three climates modeled (Phoenix, Washington DC, and Minneapolis) compared to a non-daylit zone at 2.34 kWh/ft<sup>2</sup>-yr. There was a greater occurrence of discomfort glare (3-7% during daytime work hours) if the occupant was in a seated view position looking at the window from the back of the room. The system is passive, needing no adjustment during the day and over the seasons and can be used as a retrofit measure in existing buildings. These results are encouraging and demonstrate how the primary daylit sidelit area can be extended well beyond the defined limits provided by the newly adopted ASHRAE 90.1-2010 code (i.e., 1.0 times the head height of the window).</p>10abidirectional scattering distribution functions10abuildings energy efficiency10adaylighting10aRadiance simulations1 aMcNeil, Andrew1 aLee, Eleanor, S.  uhttps://facades.lbl.gov/publications/annual-daylighting-performance