The existing lighting in these buildings was upgraded. A number of existing lighting schemes were covered, mostly recessed fixtures, some of which were controlled by occupancy sensors and time scheduling systems.
The new systems covered several options, notably a suspended 4-ft. direct/indirect three-lamp T8 fluorescent fixture from Philips Lightolier, which was mounted over the cubicles in open offices. In this fixture, one lamp produced uplight, and the other two produced downlight.
The lamps were powered by LumEnergi iB-100 digital dimmable ballasts that were controlled by an onboard PIR occupancy sensor, which dimmed the downward lamps to a low power level when the cubicle was unoccupied, and a centralized LumEnergi digital lighting control system for task tuning and personal dimming control. The control system was controlled by a system operator via a desktop computer and lighting controller. (Note LumEnergi ceased operations March 19, 2013; its assets were acquired by Fulham.)
After installation of the new fixtures, controls and new wiring, and setup of the control system, the manufacturer and installer verified operation and settings. This included confirming IP addresses and refining light level settings according to user preferences.
Other upgrades included 8-ft. workstation-specific fixtures above open office cubicles, 2×4 and 2×2 recessed fixtures in private offices and conference rooms, and 26W compact fluorescent downlights in some transition spaces. Photosensors were installed in private offices to implement daylight harvesting as an additional control strategy.
Default dim settings for task tuning control for all lighting were implemented by the system operator based on evaluation of tasks with user input. This resulted in installed power being reduced by 50 percent for the downlight component and 30 percent for the uplight component of the direct/indirect fixtures. In interior private offices, conference rooms and transition spaces, 50 percent. In perimeter private office and conference rooms, 30-70 percent. Personal dimming control was also enacted through the operator.
Despite this dimming, light levels generally improved compared to the previous system due to a higher density of fixtures configured in the new workstation-specific layout. Based on a sampling of pre-retrofit desktop light levels, 42 percent of the existing lighting was providing light levels higher than the IES-recommended 35 footcandles, while 60 percent of the workstation-specific fixtures did on the default dim settings.
The higher density of fixtures increased the lighting power density, but the control system delivered 27-63% energy savings, resulting in a net improvement in energy efficiency. The sweet spot for savings: buildings/spaces that operated 14+ hours per day, utility rates above $0.10/kWh, and variable occupancy patterns.
The researchers reported: “For all sites except Roybal, this study has shown that responsive lighting controls can achieve energy savings of about 30% compared to measured baseline conditions. These savings resulted in an average energy use reduction of about 0.9 kWh/sq.ft./year.”
As part of the study, occupants were surveyed. Generally, they reported finding the new system to deliver better quality light with less glare. Satisfaction tended to increase if the survey were conducted well after installation, providing users the chance to get used to the new system. A significant number of users, however, said the occupancy sensors would turn OFF while the space was still occupied, suggesting a lack of sensitivity to fine motion. Occupants also wanted more control of their lighting; due to GSA security restrictions, open office occupants had to go through the systems operator to change their light levels. Providing full control to occupants may have improved occupant satisfaction and generated even higher energy savings.
The researchers cited several other lessons learned that could have improved results, including personnel training, more thorough commissioning and built-in diagnostics and more intuitive operator interface and settings for the control system.
Overall, however, they concluded: “This study demonstrated that overall, responsive lighting systems have proven their ability to achieve deep energy savings while providing comparable or improved light levels and increased occupant satisfaction compared to existing GSA lighting systems.”
The report was produced as part of the GSA Green Proving Ground program, which leverages the GSA’s real estate portfolio to evaluate innovative building technologies and support the development of GSA performance specifications.
Download it here.