Occupant Responsive Lighting
Findings, September 2012
Responsive Lighting Systems Save Energy
Despite widespread adoption of efficient lamps and ballasts over the past several decades, lighting still accounts for more than a third of the electricity used in U.S. office buildings. With a real estate portfolio of more than 9,600 assets nationwide, most of which include open office space, GSA has an abiding interest in identifying energy-efficient lighting solutions that can help its client agencies conserve energy and reduce costs. Toward that end, GSA’s Green Proving Ground (GPG) program recently evaluated the performance of occupant responsive lighting technology in five federal buildings. The technology consisted of a workstation-specific (WS) lighting system, dimmable ballasts, occupancy sensors at each WS luminaire, and a Lighting Management Control System (LMCS) that coordinated these components. Seven sites were selected within the five buildings to capture a diverse group of agencies, occupancy patterns, work styles, and site and baseline conditions. Results showed energy savings that ranged from 27% over baseline conditions for spaces illuminated 12 hours a day, five days a week, with regular occupancy patterns, to 63% for a call center illuminated 18 hours a day, 7 days a week. In the call center, payback was less than 7 years.
What We Did
EXPERTS FOCUSED ASSESSMENT ON THREE CONTROL STRATEGIES
The Green Proving Ground (GPG) program worked with the Department of Energy’s Lawrence Berkeley National Laboratory (LBNL) to select demonstration sites and compare the performance of WS lighting systems to the systems in place prior to retrofits. In general, pre-retrofit lighting systems consisted of recessed luminaires that were regularly spaced in open areas or distributed based on layout in private offices. They used neither dimmable ballasts nor photocells, though some did employ zonal occupancy sensors. Retrofit systems, by contrast, were centered over each cubical in the open office and provided both upward-directed (ambient) and downward-directed (task) light; the up-light and down-light components had separate ballasts and could be controlled individually. Although responsive lighting systems can employ a multitude of control strategies, LBNL’s evaluation focused on three: institutional tuning and scheduling (where building managers program default light levels and hours of operation within the LMCS); occupancy sensing (which adjusts light levels in response to the presence or absence of occupants); and personal control (where occupants adjust WS light levels to suit their preferences).
What We Measured
EVALUATION TRACKED CRITICAL METRICS
Circuits supplying power to lighting fixtures were metered during both pre- and post-retrofit periods at each site. Power data was converted to lighting power density (LPD), which was converted in turn to energy use intensity (EUI), the unit of measurement used to describe building energy use. Finally, EUIs were calculated for each site based on an assumed typical distribution of 251 weekdays, 104 weekend days, and 10 holidays per year. Pre-retrofit and post-retrofit annual EUIs were then compared to determine energy savings at each site. Greenhouse gas (GHG) emissions were also summarized. Desktop illuminance levels were taken in open office workspaces, and an assessment of the economic benefits resulting from this project was performed. Last, occupant surveys were administered before and after the lighting retrofit at each site.
What We Found
What We Concluded
SPACES WITH LONG OPERATING HOURS AND VARYING OCCUPANCY PATTERNS BENEFIT MOST
The workstation-specific (WS) lighting systems evaluated in this study delivered deep energy savings, comparable if not superior light levels, and increased occupant satisfaction. They were found to be most cost effective in spaces with long operating hours and varying occupancy patterns, such as the call center cited above. Greater implementation of personal controls, which would allow occupants to set and adjust light levels in real time within boundaries set by building policy, would result in still better performance.
TRAINING AND TRANSPARENCY COULD IMPROVE PERFORMANCE
This demonstration study revealed a variety of lessons for responsive lighting control retrofits. They include the following:
- THROUGH COMMISSIONING IS ESSENTIAL
For the most part, formal and well-documented commissioning did not occur in the study areas. This impeded performance and in some cases resulted in extended work to address occupant complaints and correct performance issues. Thorough commissioning that is both transparent and well-documented is essential to providing lighting systems that match owner intent, operate effectively, and can be maintained over time.
- CONTROL INTERFACE MUST BE INTUITIVE
The control system studied here presented some challenges for post-commissioning operation and a steep learning curve for system operators. Advanced lighting control systems should be intuitive to operate, with well-designed user interfaces and useful data presentation. Related, appropriate training should be provided to operators in order to counter the steep learning curve and maintain investment in the commissioning process.
- PERSONAL CONTROLS CAN IMPROVE PERFORMANCE
Because of GSA security restrictions and a lack of understanding on the part of occupants about how to request changes in light level settings, personal control was implemented infrequently during this study. This should be remedied. Direct and easily accessible control over workspace light levels allow occupants to obtain the full benefits of the WS lighting system, which could result in increased energy savings, increased satisfaction, and improved performance.
For more information, contact: Kevin Powell, Green Proving Ground Program Manager.
These Findings are based on the report, “Responsive Lighting Solutions,” which can be downloaded here.
Reference above to any specific commercial product, process or service does not constitute or imply its endorsement, recommendation or favoring by the United States Government or any agency thereof.