Federal Energy Managers See Daylight To Energy Savings
April 1, 2002
Federal energy managers working to cut energy costs are finding that the decision to implement daylighting projects can be an easy one. Daylighting significantly cuts energy use for lighting building interiors—reductions of up to 75 or 80�percent have been seen in some facilities. Projects usually have a short payback period, and daylighting has wide applicability to many different types of buildings.
|This illustration of a daylighting device redirects sun to both the north and south sides of the shaft. A reflector array beneath a small opening reflects diffuse light to the ceiling, as well as distributes diffuse light to the area directly below the reflector.|
Proper daylighting involves much more than simply adding windows or skylights to a space. Daylighting is the method of admitting maximum natural light, while balancing heat gain and loss, glare control, and variations in daylight availability. Successful daylighting is implemented through proper design, placement, and orientation of skylights, clerestories (vented skylights), and other sources of natural light.
Some daylighting devices resemble conventional skylights but eliminate the problems of glare, inadequate light distribution, and poor thermal insulation that often occur with skylights. These devices may have a clear dome shape or have a hemispherical shape. Daylight is guided from the dome to the room with a reflective shaft. A diffuser at the bottom of the shaft ensures that both glare and heat from the direct beam is minimized. In many units, dead air spaces built into the system reduce the heat loss or gain typically experienced with standard skylights.
Commercial daylighting devices are either passive or active units. Passive units have no controls, but active units have mirrors under the dome that track the sun to increase the hours of useful sunlight available to the device. Some units have louvers that control and filter light. Commercial units also have automatic lighting controls that turn off artificial lighting when daylight devices produce sufficient light levels.
The benefits of daylighting projects are numerous. Most important is the energy savings derived from minimizing or eliminating the need for artificial light. The DOE National Renewable Energy Laboratory's (NREL's) Thermal Test Facility, located in Golden, Colorado, was designed with stepped, clerestory windows. The building uses 75�percent less energy for lighting than a building without daylighting features. Except for the central service area, NREL's Thermal Test Facility is lit entirely by daylight entering through clerestory windows. Additionally, daylighting decreases the energy load imposed on a building's mechanical cooling system. The energy savings from reduced electrical lighting can reduce energy use an additional 10 to 20�percent. As a result, for many commercial buildings, total energy costs can be reduced by as much as one-third through the optimal integration of daylighting strategies. Good lighting controls that turn off lights when daylight provides enough light are a very important element for achieving energy and cost savings.
Daylighting can also increase the comfort of building occupants. Although difficult to quantify, daylighting generally improves occupant satisfaction and visual comfort, leading to better performance. The human eye can adapt easily to natural light, and the light gives occupants a pleasant connection with the outdoors. Various studies suggest that daylighting increases worker productivity, benefits student learning and health, and contributes to higher sales in retail stores. Most energy managers are familiar with the fast payback on conventional building lighting upgrades, but many are surprised that daylighting projects frequently pay back just as fast or faster. A hangar at Fort Huachuca, near Tucson, Arizona, was retrofitted with 36 daylighting units at a total cost of $45,000. Each unit installed displaced a 1,175-watt light fixture. The daylighting devices were carefully monitored over a 35-month period to assess the energy savings. Over the monitored period, the daylighting devices saved a total of 268,990�kilowatthours of electricity. Including the demand charge savings, the annual savings was $9,600 per year, producing a simple payback of only 4.7 years. This short payback makes this technology an attractive opportunity for energy savings performance contracts.
Daylighting technology has been used extensively at Fort Huachuca for several years. In the past 4�years alone, 400 daylighting units have been mounted in 22 buildings on the post, demonstrating the wide applicability of the technology. At the Marine Corps Air Station in Yuma, Arizona, the devices have also been widely used. In conjunction with the local utility's demand side management program, 226 units have been installed in 7�buildings, including warehouses, a vehicle maintenance bay, and a gymnasium.
Daylighting devices have been installed in DOD housing, aircraft hangars, auto shops, child development centers, machine shops, stores, and office buildings. These devices have been installed on various roof types, including metal roofs with slopes, flat roofs, and built-up, low-slope roofs.
Energy managers experienced with daylighting projects point out there are pitfalls to avoid to ensure successful projects. Avoiding glare and overheating is essential. Lockable covers should be installed on the automatic lighting controls to prevent occupants from tampering with the adjustments and defeating cost-efficient operation. The walls, floors, and ceilings of daylighted rooms should be painted a light color to provide uniform light distribution. Roofs where the systems are to be installed should be watertight and free of lead paint. Finally, it is usually most successful to have a single contractor supply and install the product.
Federal energy managers have learned that daylighting strategies can make Federal facilities more energy efficient, more comfortable, less expensive to maintain, and more environmentally benign. Share your success stories. If you are making daylighting projects happen at your Federal facility, please submit your project descriptions to Annie Haskins at firstname.lastname@example.org.
For more information, please contact Dave Menicucci of Sandia National Laboratories at 505-844-3077 or email@example.com; Ron Durfey of MCAS Yuma, Arizona, at 928-269-2734 or firstname.lastname@example.org; or Bill Stein of Fort Huachuca, Arizona, at 520-533-1861 or email@example.com.
To learn more about daylighting and other sustainable building design strategies, make plans to attend FEMP's Designing Low-Energy, Sustainable Buildings on April 18-19, 2002, in Golden, Colorado. For more information on this training and the web-based course, please see www.sbicouncil.org. Also the National Institute of Building Sciences' "Whole Building Design Guide" provides helpful information on daylighting techniques and strategies. The guide is available at www.wbdg.org.