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Integrated Daylight Harvesting Systems Reduce Energy Consumption in Federal Buildings

The GSA Green Proving Ground (GPG) has been testing cutting edge sustainable technology in our federal buildings, and the results of such tests have shown some significant energy savings. Recently, the GPG commissioned Lawrence Berkeley National Laboratory to assess the performance of daylight harvesting at five federal buildings. Findings from this assessment revealed average annual energy savings of 27% with a payback as low as four years.

Office space lights are frequently left on during the day, even in areas fully illuminated by sunlight. In fact, at 26%, electric lighting accounts for the largest percentage of all electricity used in U.S. commercial office buildings. Daylight harvesting, the use of natural light to offset electric light in perimeter workspaces, offers the opportunity to reduce lighting consumption significantly.  

Daylight harvesting requires the use of an Integrated Daylighting System (IDS), which measures prevailing natural light against predetermined lighting set-points.  The IDS then signals automatic electronic dimming to minimize electric light output accordingly. Photo sensors are calibrated by exposing them to minimum and maximum light levels, enabling the sensors to provide accurate signals and maintain a programmed light level. In well-calibrated systems, electric light supplements natural light only as needed, reducing the use of electricity without compromising the comfort and effectiveness of workplace lighting. This can also result in savings by extending the lamp life for interior lighting fixtures.  

Energy savings are estimated to be between 20% and 60%, assuming that daylight harvesting is only one component of an integrated lighting control system. Download the full GPG Report on Integrated Daylighting Systems for more information.

This article is part of the Fall 2014 issue of the FOCUS newsletter. Please visit the Focus Newsletter page to read our newsletter. To subscribe to FOCUS, complete the online subscription form.


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