Comparison of control options in private offices in an advanced lighting controls testbed

In a major test of different lighting control technologies in a typical office building, we present analyses of seven months' results from five control scenarios in private offices. We compare the energy savings and effectiveness of various combinations of occupant detection, daylight dimming, and switching techniques. Comparing measured energy use with occupant sensors against baseline energy use calculated using wall switch operation only, we found occupant sensors saved 20-26 percent lighting energy compared to manual switching alone. In offices where light sensor controls were: installed and properly commissioned, additional savings up to 27 percent for a total of 46 percent were obtained over a seven-month period, even in an area with unusually high minimum lighting requirements. Dimming the lighting system to desired task levels (task tuning) also resulted in significant (23 percent additional, 43 percent total) energy savings in over lighted areas. On the base case floor, where only bi-level switches were installed, we found significant usage of only one switch resulting in an additional 23 percent savings over single-level switches, an unexpected result with implications for building code requirements. We found the energy savings due to occupant sensing vs. dimming depended on the behavior of occupants. In offices whose occupants tended to stay at their desks all day, dimming controls saved more energy and vice versa. The lighting requirements of occupants appear to depend on their type of work.