Sidebar: The Folly of Building-Integrated Wind
The Bahrain World Trade Center and China’s Pearl River Tower provide examples of how building-integrated wind is being used in high-profile green projects.
Bahrain World Trade Center
The dramatic, 50-story, sail-shaped twin towers of the Bahrain World Trade Center (BWTC) in Manama, Bahrain, designed by the U.K.-based Atkins Design Studio (photos main story), features the first commercial-scale, building-integrated wind-energy system in the world. Three modified, 225 kW turbines made by the Danish company Norwin A/S are mounted on bridges spanning the two towers. In this configuration, the turbines are stationary, oriented to capture the prevailing winds coming off the Arabian Gulf. Initial testing of the BWTC turbines started in April 2008, and the turbines began regular operation in December 2008, according to Ole Sangill, executive director of Norwin. While Sangill could not provide actual measured output, Atkins estimates that the system will generate 1,100–1,300 MWh annually, or 11%–15% of the building’s electricity needs. Each of the turbines is designed to achieve the full 225 kW output at wind speeds of 35–40 mph (16–18 m/s), according to Sangill, and they begin generating power at wind speeds of about 9 mph (4 m/s). According to Atkins, the geometry of the towers funnels wind into the turbines and should amplify wind speeds by up to 30%. Having such large turbines—each is 95 feet (29 m) in diameter—so close to occupied space raises concerns about noise and vibration. This is not a problem, according to Sangill. “We absolutely do not have problems with noise or vibration transferring into the buildings,” he said. EBN was not able to independently confirm this statement.
Pearl River Tower
While the Bahrain World Trade Center is the first large building to be completed with an integrated wind system, the dramatic, 71-story, 2.3 million square-foot (210,000 m2) Pearl River Tower in Guangzhou, China, designed by Skidmore, Owings & Merrill (SOM), has received almost as much attention. The building, currently under construction, will have four openings that extend through the broad face of the building, two about one-third of the way up and the other two about two-thirds of the way up. At these openings, prevailing winds will be funneled into vertical-axis wind turbines, generating electricity. According to Roger Frechette, who led the engineering team at SOM, “Based on our CFD [computational fluid dynamics] modeling and wind tunnel testing, we will be able to more than double the velocity [of the wind].” The actual turbines being used are made by Windside. Compared with those at the Bahrain World Trade Center, however, these turbines will be quite small, generating at most a few kW of electricity and satisfying no more than 2%–3% of the building’s electricity demand. Noise and vibration are being addressed in several ways. For starters, the turbines are very quiet. The turbines will be located on unoccupied floors, and Frechette doesn’t expect any noise transferring into occupied floors. Further acoustic control will be provided by the double-envelope design—a layer of insulated glass on the exterior and a single layer of glass on the interior separated by 12 inches (300 mm), with air moving through the cavity. Surprisingly, Frechette said that the building-integrated wind system actually benefits the structure. He told EBN that the openings for the turbines create a “pressure release valve” that “actually relieved some of the wind forces on the building.” He thinks that the savings in steel and concrete realized by reducing the loading might actually pay for the turbines—though the turbines are a relatively small part of the cost of this building-integrated wind design.
