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Sidelighting Photocontrols
Sidelighting Photocontrols Study Released
This study describes the current status and performance of photocontrols in those daylit buildings utilizing a "sidelighting strategy", i.e. with daylight entering a space from windows along the walls rather than from above.
Daylighting has the potential to greatly reduce energy use for electric lighting and peak electric demand in commercial buildings. The technical potential of daylighting energy savings has been estimated as high as 2 to 5 kWh/sf-yr, based on monitored performance. In this field study, it was found that the top performing quartile of photocontrol systems averaged 51% lighting energy savings (1.1 kWh/sf/yr), and a net peak demand reduction of 0.6 W-sf in daylit areas that they controlled. These values provide a reasonable approximation for the "achievable potential" of sidelit control savings, based on current design, installation, and operating conditions in west coast buildings. If these savings could be achieved in one quarter of the applicable area in new construction in California, about 9 GWh2 of new savings would be added each year, along with 5 MW of demand reduction. In the Northwest these numbers are about 2 GWh and 1 MW. If the same assumptions were applied to the existing national commercial building stock at 58 billion sf, the savings would be 3,190 GWh per year and 1,740 MW, or about the capacity of four medium-sized power plants.
In order to gather candidate buildings for this field study, extensive professional networks were tapped to identify 369 buildings that would potentially fit the study criteria, with daylight provided primarily from the side, and photocontrols installed to reduce electric lighting energy use. A phone survey was conducted with the building managers of 162 of these buildings to verify the status of daylighting, to collect preliminary information and to recruit sites for more detailed on-site surveys. Ultimately, 56 of these buildings were visited, and the monitored performance of 123 spaces in 49 of these buildings was included in the analysis.
General Findings
Of the 123 spaces with installed photocontrols, the average RSR was 0.23, meaning that on average the systems were saving 23% of expected savings, given the design of the space and system. However, 64 (52%) of these systems were not functioning at all. Of the 59 (48%) functioning systems, the average RSR was 0.53, suggesting that they were actually saving about one half of what they might be expected to save. The average lighting energy savings per square foot of photocontrolled area was 0.4 kWh/sf-yr for the whole population, 0.7 for the functioning systems, and 1.1 for the top quartile high functioning systems with (i.e. those with RSR>0.5).
We also calculated whole building demand savings of the systems during peak summer electricity use, and found the whole population averaged 0.2 W/sf, while the functioning systems averaged 0.4 W/sf and the high functioning systems averaged 0.6 W/sf of photocontrolled area. The DOE-2 analysis predicted that on average the 123 spaces should be saving 4.3 Full Load Hours (FLH) of lighting energy per day, or 57% of their normal 7.5 hrs of lighting energy use. However, monitored use showed an average of only 1 FLH of savings, or only 14% energy savings. The 59 functional systems were saving 2.2 FLH out of 6.8 hrs of normal use, or 32% savings. The highest performing system in our study, a gymnasium corridor, was saving 10.8 FLH, or 90% of all daylit hours per year.
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