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Integration is Critical
The presence of daylight influences design of electric lighting and control systems. In the daylit zones, controls are necessary to maximize energy savings.

At the 47,000-sq-ft Dena Boer Elementary School in Salida, Calif., a Kenneth K. Kaestner & Associates (Modesto, Calif.) design incorporates deep overhangs at vertical windows and triple-glazed prismatic, spectrally selected acrylic skylights. Prisms refract light throughout classrooms, offices, multi-purpose rooms and the school library. Daylight alone is capable of providing 100 percent of the school’s lighting needs (at up to 250 foot-candles) for much of the year.

The spectrally selective glazing allows visible light into the school interior while rejecting most ultra-violet and long-wave radiation that produces heat, but no light.

Electric louvers control the amount of light from the skylights, but other daylight controls are absent. The addition of dimmable electronic ballasts and a photocell-based control system offer the potential for up to $9,000 (1.85 kWh/sq ft-yr) in additional energy savings annually, says Kaestner.

At the Gymboree Corporation’s 270,000-sq-ft distribution center in Dixon, Calif., 360 4 ft X 8 ft prismatic skylights, are controlled by photosensors that send signals to controllers to dim or turn off electric lights. Occupancy sensors in about 60 percent of the building and bi-level controlled high-intensity discharge luminaires contribute to annual energy savings of about $28,000, 1.2 kWh/sq ft-yr.

Cost Effectiveness of Daylighting
To be cost-effective, the savings on lighting and cooling must offset the costs of buying, installing, and operating daylighting features in a reasonable amount of time. Typically, and depending upon the percentage of the total construction budget devoted to daylighting, the payback period is from two to five years, say industry sources.

The amount of energy savings depends on climate, location, energy load, and design of the building. Gains or losses in worker productivity are more difficult to quantify.

Perhaps, surprisingly, says Loisos, daylighting can reduce overall construction costs—through dramatic reductions of mechanical system costs. Loisos says an unsuccessful entry (by Barcelona-based Benedetta Tagliabue) in the competition for the $170-million California Department of Transportation’s downtown Los Angeles headquarters (now in design by L.A.-based Thomas Mayne) would have done just that. The system designed by Loisos and Tagliabue incorporated the latest iteration of prismatic, light-redirecting glazing to overcome the common problem of glare resulting from direct sunlight in working areas. “It was the most sophisticated façade we ever designed,” Loisos says.

The use of direct, diffuse, or reflected sunlight to provide full or supplemental lighting combined with energy-efficient lighting and electronic ballasts, has the potential to reduce the lighting power density, often the measurement of lighting efficiency, in office buildings from 2.2 W/sq ft to 0.88 W/sq ft, according to a 2001 study by the Paris-based International Energy Agency (IEA). (To measure lighting power density, add all of the potential power requirements for lighting in the building and divide that sum by the total usable floor area of the building.) The agency, which partnered with California’s Lawrence Berkeley National Laboratory to show the potential of new daylighting technologies, says that while the correlation between daylighting and energy savings is clear, “robust models for integrated evaluation of daylighting concepts are not yet available.”

The Weidt Group estimates its design of a high-performance glazing system with daylighting controls at the Skokie, Ill. Pharmacia Laboratory Building, resulted in a 38 percent annual saving in energy and operating costs. Daylighting installations at Pharmacia, utilizing high-efficiency lighting designs with controls and high-efficiency chillers, motors and heat recovery, also resulted in abatement of 16 million pounds of air pollution per year.

“Successful daylighting design requires complex tradeoffs,” says the chairman of the IEA Task 31 (daylighting) subcommittee. “Optimization can be particularly difficult because there are numerous physical parameters to consider as well as a number of performance objectives and complex time-dependent issues.”

Click for Additional Required Reading As part of this learning activity, you are required to read the following additional material: “Analyzing Daylighting Designs,” “Daylighting in Schools,” and “Skylighting and Retail Sales.” They will provide you with information on software available to analyze your designs and further details on the Heschong-Mahone Group’s study. To receive a faxed copy of the material, contact Sharon Harper, Marketing Department, 800-869-4567 ext. 130 or email SLHARPER@vistawall.com.

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