By Craig DiLouie
A new office lighting field study demonstrates that multiple control strategies can be combined successfully to generate persistent lighting energy savings as high as 47 percent in open-plan offices while improving occupant job and environmental satisfaction.
"The industry has long sought objective evidence that lighting controls not only save energy but also benefit organizations in other ways, such as occupant satisfaction," says Guy Newsham, PhD, senior research officer for Natural Resources Council Canada (NRC) — Institute for Research in Construction. "This research provides such evidence."
The study — the result of collaboration between NRC, Public Works and Government Services Canada, BC Hydro Power Smart, Program on Energy Research and Development, and Ledalite Architectural Products — was designed to confirm laboratory research while addressing persistence in savings and occupant satisfaction.
The building selected for the project was attractive for several reasons. First, it contained a sophisticated control system operating in an open-plan office setting, an environment often perceived as unfriendly to sophisticated control strategies due to issues such as poor uniformity, jurisdiction conflicts, and false triggering of occupancy sensors. Second, it combined three control strategies: daylight harvesting (via a dimming ballast and photosensor integrated into direct/indirect light fixtures located centrally over cubicle workstations), occupancy sensing (via occupancy sensor/switch integrated into the fixtures), and individual user dimming control (via dimming ballast in the fixture and control interface on user computer screens). Researchers would be able to individually estimate the relative contributions of each control type to the realized energy savings. Third, the control system had already been in operation for 4 years. Finally, the site manager let the research team not only monitor energy savings but also survey occupants about environmental and job satisfaction.
Just before the study was initiated, the system was recalibrated and monitoring software was installed to collect detailed data over a 1-year period. Occupants working in 86 workstations on several floors of the building participated by using the advanced controls while occupants on a neighboring floor used a standard fixed-output system consisting of recessed deep-cell parabolic fixtures, allowing a comparison between the two groups.
The direct/indirect lighting fixture scheme produced light levels comparable to the conventional recessed parabolic fixture system for 42 percent less installed wattage. The direct/indirect fixtures with the advanced controls operating produced a combined 42 to 47 percent energy savings compared to the same fixtures without the controls in operation and energy savings of 67 to 69 percent compared to the conventional system. Surveys of the participating occupants indicated that the advanced lighting system correlated with higher occupant environmental and job satisfaction. The site manager estimated a simple payback for the advanced system, based on energy cost savings alone, to be 2 to 4 years in a new installation and 4 to 12 years in a retrofit installation.
If installed alone, the occupancy sensors would have produced an estimated average 35 percent savings — daylight harvesting 20 percent and individual dimming control 11 percent. Daylight harvesting savings were higher in perimeter workstations, as would be expected (due to closer proximity to windows), and the researchers estimate that savings would have matched the occupancy sensor savings with some modification of the control parameters. Newsham credits the success of the installation in part to the presence of a dedicated local employee ensuring that the system was well maintained.
"This study demonstrates that the right package of controls, properly maintained, can be successfully applied in open-plan offices and produce large, persistent energy and demand savings coupled with benefits to occupants and their organizations," concludes Newsham. "Although such systems do have a higher initial cost than standard office lighting systems, the overall benefits may justify the investment, especially in the context of other investments organizations make in their employees and their work environments."
View the complete study on the NRC site.
Craig DiLouie (firstname.lastname@example.org), a lighting industry journalist, analyst, and marketing consultant, is principal of ZING Communications.