More stringent energy code requirements have fueled daylight harvesting. Big in California and the Pacific Northwest, daylighting can be used everywhere the sun shines—even in cloudy Seattle. When properly designed and efficiently integrated with electric lighting systems, daylighting offers significant energy savings by offsetting a portion of the energy load, the U.S. Department of Energy claims in the Energy Renewable Energy Building Technologies Program. Daylighting also improves occupant satisfaction and comfort.
Tinted glass and daylighting
Building owners and architects are specifying low-E glass. These coatings can transmit substantial amounts of daylight while blocking as much solar heat transmission as possible. Increased daylight transmission reduces artificial lighting and utility costs year-round. According to Chris Dolan, director of commercial glass programs for Guardian Industries, better solar control in summer reduces air conditioning costs, while better thermal performance in winter cuts heating costs. Low-E glass helps contractors harvest daylight while offering enhanced solar control to conserve energy.
Abby Vogen Horn of the Daylighting Collaborative at the Energy Center of Wisconsin said letting in all the light can be poor design.
“The solar disk, even on an overcast day, provides many times more light than is typically needed. Paying careful attention to window-to-wall ratios in addition to visible light transmittance of glazing (will vary by region and by each side of the building) is key to ensure daylight is utilized but won’t create a greenhouse. Tinted glass, which should be spectrally neutral (gray), appears darker because it actively reduces the visible light transmitted through the glass into the building interior.”
Another controls perspective
Although electrical contractors don’t have much to do with glass and skylight-dependent daylighting, there are many other areas in which the EC can affect natural lighting plans. Several of the areas include lighting and window shade controls.
According to Eric Lind, commercial marketing director at Lutron Electronics Co., daylighting systems are becoming easier to install and maintain. New systems are much more flexible, allowing easy integration with other energy-efficient lighting strategies.
Lind said the basic daylighting “operating formula” has remained consistent: Install daylight sensors within about two times the effective height of the closest window, assuming standard window/room design and reflectivity. The daylight sensor’s view toward the window should have no obstruction. It should not be positioned in the well of a skylight or above indirect lighting fixtures.
Will Howe, Lutron product development manager, said it now is possible to control lighting a space independently from the ability to achieve daylight harvesting.
“Previously, building owners considering a lighting control system thought they had to choose one or the other. Because of technological advancements, such as digitally addressable ballast, less hardwiring is necessary. ECs can ‘zone’ a room, with the lighting oriented perpendicular to the windows while, at the same time, daylight harvesting can occur parallel to the windows,” Howe said.
Howe said Lutron’s EcoSystem lighting control solution allows any combination of sensors or wall controls to be connected to its digitally addressable ballast. Because there is no need for interfaces or power packs, sensors (and wall stations) can be removed or added with simple Class 2 connections at any fixture.
EcoSystem lighting controls provide installers with control wiring options enabling customizing the installation to fit the job. The control wiring can be either Class 1, which runs in conduit with the power wiring, or Class 2, which is wired in a cable tray or with other communication wiring. Installers generally prefer control wiring that can be run in the conduit with the power wiring (Class 1), eliminating the need for extra conduit or wiring time. Modular cable can be used to quickly connect fixtures and drastically reduce overall wiring time in new construction. If desired, the control wiring also can be wired as Class 2 in cable tray or with other harmless communication wiring (for retrofit applications).
In addition, installers can select their preferred wiring format—daisy-chain, star method or T-tap-—because the control wiring is topology-free. It’s also polarity-free. If the control wiring is reversed when connected, the ballast will still operate.
“Whether the control wiring is Class 1 or Class 2, the sensors and wall stations are easily added or removed with simple Class 2 connections at any fixture. Free from interfaces and power packs, there are fewer parts and pieces required for installation,” Howe said.
Only one daylight sensor should be earmarked for each 30-foot zone of fenestration, he said.
“As now equipped, wiring a daylight sensor to a single ballast allows control of multiple ballasts on the bus. The digital ballast accepts only one IR input, so use of the IR input for the daylight sensor precludes the use of an infrared receiver with the same ballast,” Howe said.
While Daylighting Collaborative’s Vogen Horn agrees daylighting controls are more efficient and user-friendly, she advises contractors to beware of the different control strategies systems use: open or closed loop.
“Open, the sensor looks to the daylighting opening and the available natural light to control the electric lights accordingly. Closed, the sensor looks down at the work surface plane, at both natural light and electric light incident on that surface and controls the electric light accordingly,” she said.
Computer modeling is becoming an important strategy for ensuring a daylighting design strategy is effective, Vogen Horn said.
“The algorithms and theory that build the engines of these modeling software programs is becoming more reliable in providing accurate information, including placement of photosensors.”
For additional information on daylighting and how to find local/regional resources, visit the Daylighting Collaborative at www.daylighting.org. A national program of the Energy Center of Wisconsin, the Daylighting Collaborative provides information on all daylighting strategies.
As daylighting marches forward, electrical contractors may well get involved. The good news is green is becoming more affordable.
WOODS writes for many consumer and trade publications. She can be reached at email@example.com.