CBS Newsletter
Spring 1997
pg. 3

Aerial view of Washington D.C.

News From the D.C. Office

Monitored Savings from Energy-Efficient Lighting in D.C. Office

More on the DC Office efficiency up-grade: Office Equipment: Part 1, Part 2

Figure 1: Lighting energy use profile for a typical exterior office.

Berkeley Lab's office in Washington, D.C. is located a few blocks from DOE headquarters, in a five-year-old office building constructed mainly for lease to Federal agencies and their contractors. Despite its recent vintage, the building's standard lighting specifications were far from today's best, cost-effective practice.

In designing the build-out plans for offices and meeting rooms in our 7,500-square-foot suite, we wanted to showcase some of the energy-efficient lighting and office equipment developed for DOE's Building Technologies program by LBNL, other laboratories, or private industry. The lighting design strategy comprised three elements: more efficient lighting equipment to reduce average lighting power densities, occupancy and daylighting controls to avoid unnecessary on-time, and effective design to take advantage of daylight and task lighting. Overall, these measures saved more than 50 percent (about 11,000 kWh/yr) compared with a building's original design.

An important part of the Lab's "practice-what-we-preach" approach was to monitor the actual performance and energy savings of these efficiency features. To streamline both the monitoring and data analysis, we used battery-powered data loggers and a user-friendly commercial software package. The results of this mini-study are discussed in this article; a future article will present savings from energy-efficient office equipment and appliances.

Efficient lighting equipment: The recessed ceiling fixtures were rewired to replace the T-12 fluorescent lamps and magnetic ballasts with high-frequency electronic ballasts and efficient, smaller-diameter T-8 lamps. This rewiring reduced power per fixture by 20 percent, from 110 watts to 88W. If the conversion of recessed ceiling fixtures to T-8 lamps and electronic ballasts were the only retrofit applied throughout this 440,000 ft2 office building, the annual savings would be about 290,000 kWh, worth $27,000/year to the building owner. We also selected thermally optimized compact fluorescent down-lights and wall-washers as well as low-power LED (light-emitting diode) exit signs, all of which meet the new Energy Star efficiency criteria as recommended for Federal purchasers. Taken together, the lighting equipment changes reduced our overall lighting power density for offices plus circulation and utility areas by 17 percent (1.3 to 1.08 W/ft2).

Lighting controls: We installed occupancy controls throughout the office to avoid lighting unoccupied rooms or those that have sufficient daylight. In the perimeter offices, we use "off-only" occupancy controls; these must be switched on manually when daylight is inadequate, but they turn off automatically after the occupant leaves. Lighting in the interior offices is controlled by conventional on/off occupancy sensor switches. Based on our monitoring of a sample of occupied offices, we found lighting savings of 68 percent in the exterior, daylit offices and 50 percent in the interior offices (Figs. 1 and 2). We have measured even greater savings from occupancy sensors in intermittently used spaces, such as the kitchenette and storage areas. Controls in the small conference room consist of a continuously dimming ballast with daylight sensor, while the large conference room uses pendant-hung fluorescent fixtures with step-dimming controls (using a wireless remote) to accommodate audiovisual presentations. In the aggregate, controls saved about 25 percent after accounting for efficient lighting equipment.

Figure 2: Lighting energy use profile for a typical interior office.

Use of daylight and task lighting: The office layout itself was designed to make the best possible use of daylighting. For example, the hallway was offset to increase daylit space (shared rather than single offices are on the window side), and interior, fixed-glass windows help bring daylight into the hallway and interior offices. Many staff keep the overhead lights off in the exterior offices, preferring natural light with occasional desktop task lighting.

—Avis Woods, Brad Gustafson, and Jeff Harris

Info icon

Jeffrey Harris
Washington D.C. Projects Office
(202) 484-0883; (202) 486-0888 fax

More on the DC Office efficiency up-grade: Office Equipment: Part 1, Part 2

This work is supported by the Federal Energy Management Program.

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