Savings from Daylight Harvesting Varies with Occupancy

July 18, 2014 By Linda Hardesty

GSA energy manageDaylight harvesting reduces lighting energy consumption by using natural light to offset electric light in perimeter workspaces. A study of five federal buildings found that daylight harvesting provided an average annual energy savings of 27 percent.

However, the study found increased savings from occupancy control left little room for savings from daylight harvesting.

GSA’s Green Proving Ground (GPG) program commissioned Lawrence Berkeley National Laboratory to assess the performance of daylight harvesting at five federal building sites, for the report “Integrated Daylighting Systems.”

The five long-term study sites with active daylighting averaged annual energy savings of 0.84 kWh/ft2 or 27 percent. Payback ranged from 4.3 to 17.6 years, with three of the five sites realizing simple payback of less than 6 years. Two sites would have had more attractive payback if they had been occupied a larger percentage of the time—greater use resulting in greater savings.

The report recommends deploying daylighting technology where existing lighting use is high. As a rule of thumb, daylight harvesting becomes cost-effective at an installed cost of $1.40/ft2, with a utility rate equal to the national average of $0.10/kWh, assuming dimming ballasts are already in place.

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