1 dec 06 | Architectural Record
SOM's Pearl River Tower; the storied design firm has set its sights on redefining one of its bread-and-butter project types, the corporate headquarters, into a model of high-tech sustainability.
Designing towers for corporate headquarters is something Skidmore, Owings & Merrill (SOM) can do in its sleep. When the firm won a competition for a tobacco company tower in the new city of Guangzhou, China, SOM's Chicago partners decided to approach the commission as a net-zero-energy-skyscraper experiment. "We knew the tower was going to get built with or without us, so we felt we might as well design it and make it as sustainable as possible," says Roger Frechette, director of m/e/p sustainable engineering at SOM.
Frechette distinguishes a "net"-zero-energy building as one that negligibly affects its local environment. In the case of the 71-story, 2.2-million-square-foot Pearl River Tower, this meant it had to conserve and generate enough power to meet its energy demands. "There is no silver bullet," Frechette says. "What we have is a series of small steps that get you to something that makes a difference." These divide into four categories: reduction, reclamation, absorption, and generation.
The designers began by reducing the building's energy consumption through a combination of the building's site orientation, a high-performance building envelope, daylighting, and building control systems. By rotating to the east, the tower takes advantage of midday sun while the effects of late-day sun on the larger, southern horizontal exposure are minimized. The south facade's low-E-glass, double-layer curtain-wall system reduces heat gain, which leads to less demand on the HVAC systems.
Reclamation and absorption
Among other tactics, the tower reclaims its energy by routing each floor's exhaust air into the south side's double-layer curtain-wall cavity. This thermal barrier of hot dry air can then be reused on the mechanical floor for passive dehumidification. Many other systems perform double duty, including the chilled slab concrete vaulted ceilings in the typical offices that enhance daylighting, as well as cool the air drifting up from the underfloor ventilation system. The main absorption strategy takes advantage of a geothermal heat sink, so 100 degrees Fahrenheit water in the mechanical system's return loop can be cooled to 75 degrees Fahrenheit prior to feeding the cooling towers.
According to Rob Bolin, SOM's associate director of sustainable design, the first three strategies reduce the building's energy use by nearly 65 percent over a baseline of Chinese building codes. To reach the final goal of net zero energy, the design team incorporated three power-generating technologies: wind, integrated photovoltaics, and microturbines.
By far the most innovative of these elements, the wind turbines exploit the prevailing winds from the south, which generate a negative pressure at the rear, or north side, of the building. The tower's curvilinear structure helps to force air through four turbine inlets in the facade, which SOM's wind studies have predicted will speed up the wind's velocity two-and-a-half times. Frechette estimates the turbines will produce nearly 15 times more electricity than a typical stand-alone wind generator.
What's more, the turbines blend seamlessly into the tower's architecture as warped cavities at mechanical floors. "The more we can blur lines, the closer we can get to true integration," Frechette says.