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Bahrain's Wind Turbine
Trio Sets Record for a Skyscraper |
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In
a region where remarkable buildings jostle for attention, the
quest for a skyscraper icon led the developer of Bahrain’s World
Trade Centre to build 29-meter-dia wind turbines into its twin
towers. The trio of turbines, the world’s largest on a building,
may not add up financially as energy sources. But they will make
the 240-m-tall “skycon” unique, while displacing up to 1,300 MWh
a year of fossil-fuel power.With elliptical floor plans, the concrete-framed towers taper like sails. Between them, three bridges span approximately 32 m. Each carries a 275-kW turbine, located midspan.
Together, the turbines will meet 11 to 15% of the building’s electricity demand. That will be equivalent to at least 55 tonnes of carbon emissions, according to the project’s local architect and engineer, WS Atkins Middle East Ltd.
Principal architect Shaun Killa spotted the energy potential of BWTC’s location, facing onshore prevailing winds, during a site visit three years ago. The client “immediately embraced” the idea of the turbines for the double benefit of the energy savings and the creation of an iconic symbol, says Killa.
A seasoned yachtsman, Killa had used his understanding of sail aerodynamics to research the best building profiles for turbines. The sail-like profiles, then designed, funnel wind into the turbines. And by creating negative pressure on the leeward side, the towers increase wind velocities. Killa knew the shape would be ideal, but he was surprised by better-than-expected performance during the towers’ wind tunnel tests.
The tests showed the wind stream to be nearly perpendicular to
the turbines up to 45° to either side of their central axes,
says Killa. It is an advantage that the blades cannot swivel
into the wind, for it “widens the operational period, producing
more energy,” he explains. “This effective envelope may prove to
be wider, say 60°, during [turbine] commissioning,” he adds.To engineer the elements of the turbines, BWTC’s undisclosed owner hired Danish structural designer Rambøll Denmark A/S, Copenhagen, in October 2004. Rambøll handles the bridge design, while Denmark’s Norwin A/S takes care of engineering, supply and installation of the turbines.
Fixed at one end and on sliding bearings at the other, the bridges weigh 77 tonnes each, including turbines. Viewed from above, the bridges have a modest boomerang shape so they stay clear of deflecting turbine blade tips, says Lars Thorbek, Rambøll’s project manager. In section, the steel-plate bridges are elliptical—5 m wide and 1.5 m deep. Because the bridges are heavy and on soft bearings, their vibrations will be “very small,” says Thorbek.
Turbine noise and vibrations were among the owner’s prime concerns, according to DTZ Bahrain, the managing and leasing agent. “We spent a considerable amount of time on the bearing design compared to the rest of the project because of the complexity of this component,” says Gene Redelinghuys, a DTZ spokeswoman.
The building’s main contractor, Nass Murray & Roberts Joint Venture, started construction of the $77-million core and shell in June 2004. The project was marred last March when 58 project staff and others drowned when their boat sank, as they celebrated the building’s topping out.
In September and October, subcontractor Almajdouie PSC Heavylift Co. Ltd. raised the bridges with strand jacks. Norwin then began installing turbines with a tower crane.
“Two out of three nacelles have been installed,” reports Simha Lytherao, Atkins’ project manager on site. The third hub is due this month, followed quickly by all three turbines’ blades. The building is due to open in the first quarter of next year, according to DTZ. But turbine commissioning and fine tuning will go on for months.
By using standard equipment and arranging the turbines off the main structures, the designers kept costs of all wind energy-related elements to under 4% of the undisclosed total building value, according to Killa.
Investment in the turbine system amounts to $3 million, notes Redelinghuys. With annual operating costs of $35,000, the turbines will save the owner nearly $59,000 a year, she adds.
But including capital investment, “it won’t be able to pay for itself with the energy prices you have in Bahrain,” says Thorbek. “It’s a very costly way of producing power, but if you were to do it again, the price would go down.”
That could be soon. “We are... designing a number of single-tower buildings with even larger-scale wind turbine integration,” says Killa.
But before they get off the ground, Thorbek is already working on another job with three wind turbines, in London. Multiplex Construction (U.K.) Ltd., plans soon to start building the 147-m-tall, $200-million Castle House residential tower in the Elephant and Castle district.
Designed by local architect Hamilton Associates, the building will incorporate a range of features that would cut energy costs per apartment by up to 40% below the current U.K. housing average, claims Multiplex. Three 9-m-dia, 16-kW wind turbines, housed in Venturi tubes passing through the tower’s top, would account for a small part of that.