Wisconsin's Solar Energy Sensing Δ 3rd of January 2014 Ω 6:00 AM

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«Solar Sensing of U.S.	Θ	Θ
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~ Daylighting Collaborative

»Daylighting Collaborative

DAYLIGHTING METRICS—Defining Successful Daylighting
ξ Daylighting has been recognized as a key strategy to reducing building energy use
ξ Yet very few buildings have a comprehensive daylighting strategy that saves energy
ξ Why not? Most designers answer that they do not have a clear definition of what successful daylighting is or performance goals their designs must achieve.
ξ Metrics would provide a path to defining effective daylighting and move us closer to realizing its potential energy savings and related environmental benefits.

AVAILABILITY OF SUFFICIENT DAYLIGHT
ξ There are minimum requirements for illumination within a space depending on occupancy, special tasks/needs and local codes.
ξ A daylit space should rely on natural light as the primary light source during daytime hours.
ξ This metric would determine if sufficient daylight is available to allow reduced use or no use of electric lighting.
ξ If sufficient daylight is available to provide adequate illumination, the space would qualify as daylit.

QUALITY OF VISUAL ENVIRONMENT
ξ This is the subjective component of daylighting design and the most difficult to assess with a single metric.
ξ This metric must consider the most significant issues regarding quality of lighting: glare and veiling reflections.
ξ Glare results when contrasts within the visual field are too great for the eye to adapt to comfortably.
ξ Veiling reflections result in the inability to see details due to reduced contrast.
ξ The difficulty in developing this metric is the fact that different tasks require different illumination levels.

ENERGY IMPACTS
ξ Daylighting strategies should be considered a failure if there is no attempt or an unsuccessful attempt to turn off or reduce electric light use when natural light is available.
ξ This metric should be tied to the energy impacts on whole building energy use
ξ to determine whether the daylighting is a performance benefit or a design amenity.
ξ This metric must consider both energy use reduction (kWh) as well as demand reduction (kW).
ξ Metrics incorporating the above elements would not define design strategies
ξ but performance goals for successful daylighting.
ξ Performance goals allow for variation in design approaches necessitated by various climates, regions, building types, etc.
ξ Once these metrics have been established, they will most likely be incorporated into LEED™ and other green building rating systems.
ξ The metrics will be used to determine points awarded for daylighting, replacing the existing Glazing Factor and Daylight Factor
ξ which have been difficult for design teams to effectively design to and calculate.
ξ Not only will these metrics be included in green building rating systems,
ξ they will help move daylighting towards standard design practice.
ξ Metrics may also help move daylighting into building codes across the county in the future
ξ some states, including California already have code language for daylighting design
ξ There currently are two efforts underway to develop daylighting metrics. The

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