Bahrain World Trade Centre, Manama, Bahrain

The Bahrain World Trade Centre on the King Faisal Highway in Manama is an extension to the existing five-star Sheraton Hotel complex (a rejuvenation) and comprises two 50-storey sail-shaped commercial office towers, which taper to a height of 240m and support three 29m diameter horizontal-axis wind turbines.

The towers are integrated on top of a three-storey podium which accommodates a new 9,600m² MODA shopping centre (160 boutique stores including Versace, Yves St Laurent, Hermes and Dolce, Tiffanys, van Cleef and Arpel and Gabbana), fine restaurants, food court, hotel space for the Sheraton, business centre and car parking.

The podium accommodates a one-storey extension to the existing shopping mall to give a total floor space of 16,500m² and this has been carried out to preserve the established modular, axial and spatial parameters of the development. The towers were officially opened in mid-2008 and tenants have been moving in.

Wind power

Inspired by Arabian wind towers (Atkins chief architect Shaun Killa was responsible for the design), the sail-shaped towers funnel the sea breeze into the three 29m-diameter wind turbines. They act as aerofoils, funnelling and accelerating the wind velocity between them.

The vertical sculpting of the towers also progressively reduces the pressure so that when combined with the rising velocity of the onshore breeze at increasing heights, a near equal regime of wind velocity on each turbine is achieved.

Understanding this phenomenon has been a key factor behind the success of this design. Extensive wind tunnel testing also confirmed how the shapes and spatial relationship of the towers sculpt the airflow, creating an 'S' flow. This ensures that within a 45° wind angle either side of the central axis, the centre of the wind stream remains perpendicular to the turbines.

The elliptical shaped towers act as aerofoils, funnelling and accelerating the wind velocity between them.

In this way, the turbines' potential to generate power is dramatically increased. The turbines are expected to produce between 11% and 15% of the building's electricity needs (generating between 1,100MWh and 1,300MWh a year) and will operate for 50% of the time with full power being generated at a windspeed of 15 to 20m/s.

The generators are of a four-pole 400V asynchronous induction type, which require little maintenance and can be controlled by centres established in the towers. There have been provisions made to mount small cranes on all on the three bridges to undertake maintenance and replacement of components on the turbines.

The three wind turbines, which have a 20-year life, were lifted into place in March 2007 and commissioned in October 2007. In April 2008 the three wind turbines turned together for the first time. The total output of each turbine is 225MW and they have been mounted at 60m, 98m and 136m high between the two towers.

This is the first successful large-scale implementation of wind turbines into a building. The problem in the past has been the high cost of developing the turbines, which can be up to 30% of the cost of the building. In this project the costs have only been around 3.5% of the project cost because of the use of more off-the-shelf technology for the turbines.

Other features

The building also incorporates a large number of other sustainable features that make it environmentally responsive in reducing carbon emissions. The deep gravel roofs in some locations provide kinetic insulation, while balconies to the sloping elevations with overhangs provide shading. Dense concrete core and floor slabs will level loads and reduce peak demand with associated reductions in air and chilled water transport systems.

There will also be water recycling, connection to the district cooling system, thermal insulation, reflection pools for evaporative cooling, low-leakage windows and thermal glass with a low solar gain.

The BWTC sets a precedent that wind turbine integration is possible in the built environment. It places environmental design on the forefront of clients' and designers' agendas in a highly visual way, and hopefully helps initiate more energy conscious developments worldwide. The cost of the wind turbine technology is not prohibitive and this project sets a benchmark for future projects.