Daylighting is the controlled admission of natural light-direct sunlight and diffused skylight-into a building to reduce electric lighting and energy consumption. By providing a direct link to the everlasting evolving patterns of outdoor illumination, daylighting helps create a visually stimulating and productive environment for building occupants, while reducing as much as one-third of the total building’s energy cost.
Daylighting is more than just skylights and windows, but is coupled with a daylight-responsive lighting control system. When there is a sufficient amount of ambient lighting provided by daylight alone, this system has the capability to reduce electric lighting power.
Implementing daylighting goes beyond listing the components to be gathered and installed. Daylighting requires an integrated design approach to be successful because effective daylighting requires involving decisions about the building form, location, climate, building components, lighting controls and lighting design criteria.
Benefits
Daylighting provides up to 37 times more efficient use of solar energy for lighting compared to photovoltaic (PV). Daylighting is the standard for color quality in lighting, with a Color Rendering Index (CRI) of 100.
Numerous studies link daylight and outside views to higher levels of satisfaction and productivity. Businesses that utilize productivity-focused, energy efficiency measures view them as a distinct competitive advantage. Daylighting can replace electric light 70 to 80 percent of daylight hours and is considerably cooler than electric lighting at the same foot-candle levels, so it also reduces the cost to air-condition buildings. This can mean tremendous energy savings in buildings that operate during the day, such as schools, offices, warehouses, factories and retail stores.
Lexington, Mass.-based TIAX’s Controls and Diagnostics Report found that dimming electric lights in daylit spaces could reduce annual lighting energy consumption in existing commercial buildings by 40 to 60 percent (New Buildings, 2001, New Buildings, 2003).
According to Jon McHugh, PE, LC, technical director with Heschong Mahone Group Inc., Gold River, Calif., America could reduce its peak load electrical demand by 24,000 megawatts just by daylighting existing buildings that could utilize toplighting or skylights. The savings is equal to 24 1,000-megawatt nuclear power plants or 48 500-megawatt coal-fired power plants, all at 1/20th the cost of photovoltaic panels.
San Francisco-based Pacific Gas and Electric Co.
(PG&E) has studied the effects of daylighting in a variety of settings. In educational classrooms, daylighting has been shown to increase productivity, grades and reduce absenteeism. The study showed that students with the most daylighting in their classrooms progressed 20 percent faster on math tests and 26 percent faster on reading tests in one year than those with the least. It also found a uniformly positive and statistically significant correlation between the presence of daylighting and better student test scores.
A PG&E study showed that with daylighting features incorporated into a 15,000-square-foot office building, the need for electrical lighting during normal operating hours was reduced, which, in turn, reduced the cooling requirements and allowed the building designers to downsize the HVAC system. Extensive monitoring of this building demonstrated that annual lighting energy (kWh) consumption was reduced by 32 percent.
The study also showed office workers performed 10 to 25 percent better on tests and recall when they had the best possible view, which also improved employees’ morale and satisfaction with their work environment.
In a retail setting, a PG&E study showed daylighting dramatically increased sales; one study showed a 40 percent increase in sales in daylit stores when compared to identical non-daylighted stores.
Properly daylit buildings can repay installation cost quickly, often in less than two years. Daylighting can be installed in buildings to replace electric lighting for 1/20 of the cost of enough solar PV panels to generate an equivalent amount of electricity using the same sun at the same high energy demand times of the day.
Why Daylighting Works
Roofing contractors and owners are skeptical of skylights because traditional skylights have a tendency to leak, allow excessive heat in and can be an OSHA nightmare due to fall-protection issues. Not all skylights are the same. Sacramento, Calif.-based Sunoptics’ patented high-performance design has been proven to eliminate leak and condensation concerns.
The double-glazed prismatic dome is sealed with a silicone and urethane seal between the prismatic lenses before it is fully welded with encapsulating and insulated thermal break. There is no exposed metal to avoid condensation from thermal bridging through the frame. The pre-installed foam curb gasket and curb weather sweep eliminates air filtration and protects against moisture infiltration. This frame then sits on a curb and is screwed in with 300 series stainless steel Sunoptics screws with rubber washers.
Reduced lighting energy use ranks as, by far, the greatest factor in annual savings at economically optimum skylight-to-floor ratios (SFR). The reduction in lighting energy use is directly related to Visible Light Transmission (VLT); i.e., the higher VLT, the lower the total skylight area needed to achieve a given lighting energy savings. Because heating and cooling energy losses are small relative to lighting energy savings, if reducing U-Value results are in any significant reduction in VLT it is generally not a beneficial tradeoff at SFRs in the range expected to be economically optimal, i.e., below 5 percent (DOE Toplighting Report June 2008).
Curb integrated fall-protection devices are made to last a lifetime with 3/16-foot galvanized cold rolled steel having 75,000 PSI tensile strength. The 3/16-inch-diameter minimizes light reduction to interior and the 4-inch and 6-inch grid pattern fulfills the OSHA 1910.23 and Cal/OSHA guidelines.
Impact of Ceiling Height
Ceiling height has a major impact upon the economics of a toplighting solution because a higher ceiling enables fewer larger skylights to be used to achieve similar lighting levels. Effective toplighting requires that light from skylights be reasonably even across a space, as is required for light from electric fixtures. A higher ceiling allows skylights to be spaced further apart because the additional height provides more distance for the light to spread horizontally outward from each skylight
(U.S. Department of Energy).
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Wes Brooker is the marketing manager at
American Buildings Co., Eufaula, Ala. To learn more,
visit www.americanbuildings.com.