It’s that time of year, when sunlight is in limited supply in the Northern hemisphere. The low angle of the sun beaming directly through office windows somehow becomes more tolerable in the winter. By summertime, however, the endearment quickly fades.
For employees in the 350,000-square-foot Consolidated Forensic Laboratory (CFL) in Washington, D.C., a six-story-tall, south facing, glass curtainwall façade would typically result in intense glare, unforgiving solar heat gain, and increased building cooling demand—counterproductive for its occupants as well as for a project that is targeting LEED Gold certification.
The facility hosts three governmental agencies—the D.C. Metropolitan Police Department, the Office of the Chief Medical Examiner, and the Department of Health. Laboratories—spaces that prefer indirect sunlight due to light-sensitive operations—occupy the north, east, and west elevations, while administrative areas are organized along the south side of the building.
The local HOK office strategized ways to mitigate the solar heat gain to help ensure a high-performance building and to create a distinctive aesthetic from other sustainable commercial buildings in the District, says project manager and senior associate Timothy O’Connell, AIA. “This building is all about celebrating sustainability as part of the design parti,” he says.
After researching different energy-efficient building skin systems for the south elevation, the firm selected an exterior automated solar sunscreen that would fulfill CFL’s aesthetic, programmatic, and sustainability goals. Covering three-quarters of the south wall, the 24,000-square-foot solar sunscreen comprises glass louvers that adjust automatically to control direct sunlight at the building perimeter while allowing indirect light to penetrate 45 feet inside the open office area.
Manufactured by British company Colt International, the louver operating system encompasses three 90-foot-square bays, each with 648 18-inch-by-64-inch nominal glass fins and 108 half-sized end fins. The 11/16-inch-thick laminated glass, manufactured by Viracon, has a 50-percent frit pattern to cut the amount of sunlight entering the building by half when the louvers are fully closed.
Structurally, the louvers are supported by vertical mullions spaced 64 inches o.c., which in turn are supported by aluminum outriggers built into the unitized curtainwall. In the vertical direction, the outriggers align with the floor plates.
The louvers operate on low-voltage screw actuators that require 1.7 amps to operate, or a total of 30.6 amps per floor. Every hour, the fins rotate based on a computer-driven system that calculates the sun’s angle using the building’s location, time of day, and time of year. A roof-mounted weather station equipped with a barometer, thermometer, windspeed monitor, and daylight sensor also informs the fins’ position, telling “the system if it is sunny or cloudy outside,” O’Connell says.
On cloudy days, at night, and during times of heavy wind, the louvers are completely open, or horizontal. During times of snow or sleet, the louvers close to prevent ice buildup. The sunscreen’s controls tie into the building management system and can be manually overridden.
Unlike a double-skin façade, which the team also considered, the solar sunscreen allows the 4-foot airspace between it and the curtainwall to vent. Otherwise, O’Donnell says, “the heat builds up in this climate, and it’s ineffective [at reducing heat gain].”
The unitized curtainwall façade was fabricated by Gardner Metal Systems (GMS) in Acworth, Ga., while components for Colt’s louver operating system came from Germany and England. “Everything met on site,” O’Connell says. In roughly five months, exterior wall contractor TSI Architectural Metals, in Upper Marlboro, Md., erected the curtainwall, installed the sunscreen’s vertical supports with actuators and brackets for the glass fins, and fitted the glass fins individually on site.
Along with helping CFL reduce energy usage by 30 percent, as compared to a baseline laboratory building, the mechanics of the automated louver system also appeal to the building’s users, O’Connell says. “This is a signature agency that needs to recruit and retain people. Scientists appreciate something as technical as this.”