Case study: Functional, efficient lighting for USACE
The U.S. Army Corps of Engineers’ offices are both functional and efficient, with low lighting power densities
Project location: Seattle
Name: Federal Center South
The 210,000-sq-ft Federal Center South serves as the new offices for the U.S. Army Corps of Engineers (USACE). Consisting of three floors open to a central atrium, the high-performance facility meets current federal energy goals for energy-use reduction, as required by the U.S. General Services Administration (GSA). These include achieving U.S. Green Building Council LEED-NC Gold requirements and Architecture 2030 Challenge energy- and carbon-reduction goals. The project goal for interior-lighting power density (LPD) is 0.7 W/sq ft. Offices are configured in a semicircle (oxbow shape) surrounding an atrium and central commons. The lighting design delineates four key conceptual and functional elements of the project: the offices, the atrium, the connecting stairs, and the commons. The office elements are clean and white in appearance while the commons are warm and welcoming.
The project is designed to highlight how things are built, as an homage to the USACE. Metal and wood ceilings are exposed, requiring lighting to be carefully integrated into architecture. Having exposed ceilings made designing a highly energy-efficient lighting system more challenging. Early studies determined that spacing high-performance fixtures 22-in.-on-center in the open-office space would align with structural bays and furniture layouts while alternating with chilled-beam locations. This integrated approach keeps the ceiling unobstructed and provides optimum lighting at the ceiling and workplane. The design team worked with light-fixture manufacturers to develop custom broad-distribution fixtures that illuminate the office space to an average of 25 fc while using 22-in.-on-center spacing.
The lighting concept delineated of lighting approaches between four program areas: indirect lighting in the offices, wall wash in the commons, minimal lighting in the atrium, and illumination of vertical surfaces at the stairs. The atrium is not illuminated and is left as a “void” lighting space, except for handrail light fixtures at bridges and landscape lighting. Allowing the atrium to be dark helps highlight the contrast between white office space and the commons warmth.
The central corridor in the commons connects the entry to an outdoor terrace. Lighting highlights wood walls and graphics along the corridor while bench-integrated footlights complement the line of connection between the entrance and terrace. Bracket-mounted linear light fixtures provide cohesive wall wash at the commons’ wood walls. All conduit and J-boxes are hidden within architectural surfaces. Lighting within the commons meeting rooms provides indirect lighting and illumination on at least one presentation wall. Vertical surfaces at the back of the stairs are washed with light to provide a destination node, indicating vertical circulation and backlighting environmental graphics etched into stair glazing.
Ballasts are addressable for ease of fine-tuning electric light load shedding during daylight hours. Photocells are located to provide for building perimeter and atrium daylight contribution. A combination of building time-clock controls and occupancy sensors ensure that light fixtures are only on when spaces are in use. Switches, dimmers, occupancy sensors, and photocells are wireless to aid in relocation and to maximize ease of use and energy savings. Energy-use projections indicate a 40% overall savings of lighting energy used, as compared with a typical office building. LPD for the project is 0.65 W/sq ft while providing 25 fc in the open office. Seattle energy code requirements call for a maximum LPD in office buildings of 0.9 W/sq ft.
The composition of illuminated forms provides a unique office environment as well as a highly functional and energy-efficient lighting system for USACE.
Melanie Taylor is vice president, and national buildings lighting design practice leader at WSP Parsons Brinckerhoff. Her expertise includes more than 25 years as an architectural lighting designer working on a diverse list of complex commercial projects.