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Twenty-eight of the units illuminate the school's 20,895 sq. ft. rectangular gymnasium. They're installed four across and seven deep along the length of the space. They're on 20-foot centers at a height of 40 feet above the floor.

An 8,100-square-foot auxiliary gym adjacent to the main gym has 12 units installed three across and four deep. Like the main gym, the units are on 20-foot centers and 36 feet above the floor.

By comparison, the 7,980-square-foot activity center has 16 units in a four-by-four pattern that are obviously much closer than on 20-foot centers, but are still 40 feet above the floor. The concentration of units produces even higher light levels that far exceed the code required 50 foot-candle level. School officials wanted the extra light for light-intense student activities, such as studying, and to evaluate as part of the ongoing design improvement process.

A flood of foot-candles

Foot-candle (fc) meter readings during a sunny morning showed 60-65 fc at 8:50 a.m. During a partly cloudy day, the meter measured 90 fc at 11 a.m. and 68 fc at 4 p.m., all well above code requirements.

Electric lighting in these common areas comprises T5 fluorescent lamps in four 4-foot troffers powered with electronic ballasts. The architectural firm selected high bay fluorescents over high intensity discharge lamps for their energy efficiency, instant-on and instant-restrike capabilities and because they can be wired for instant switching between light levels.

The electric lighting was not downsized since the spaces are multi-purpose and used at night so they need to meet the code-required 50 foot-candle level, which is modeled after IESNA1. standards. Switches and timers control the lighting. If the lighting is not needed, occupants have the option of turning it off.

Four resource classrooms and a prep room on the school's second story each have two daylighting units at a ceiling height of 10 feet. Electric lighting for these spaces also is fluorescent lamps, but is connected to motion sensors for automated on-off control. The daylighting units can be an integral part of a daylight harvesting system.

Lynn Coles, the project superintendent for the school's general contractor, Sletten Inc., commented on the amount of light the daylighting units pour into the spaces. "The areas are highly illuminated," he said. "Electric lighting could be turned off during the day, absolutely."

How much electricity will the units save during the school's first year of operation? Rather than estimate savings, school officials decided to compare electricity consumption after the school completed its first year of operation—the 2008-2009 school year.

Since Desert Oasis is otherwise similar in design to the three schools without active daylighting units, it ought to be easy to determine the difference.

The architectural firm and school district officials are confident the daylighting units will perform as expected so it was a 'no brainer' to specify them for the fifth prototype school as well. And rightfully so.

In other installations in the U.S., Canada, Central America and Europe, the units are producing anywhere from a 15 percent to better than 40 percent return on investment. They enable electric lighting to be turned off completely for more than 10 hours a day. This experience suggests the potential savings for the high school.

Based on producing the equivalent illumination of 800W of fluorescent lighting per unit, the 66 units would save 52,800W, or 52.8 kW, school-wide.

Multiplying that number by the 10 hours on average that the fluorescent lighting could be turned off every day totals 528 kWh a day and 95,040 kWh for a school year lasting an average of 180 days.

At the 7.8 cent kWh rate that the school pays for electricity, the savings in taxpayer dollars could total $7,413 a school year. The multi-purpose gyms and other common areas will be used more than 180 days a year, which will further boost energy savings.