City Hall - a 'green' building

The energy strategy for City Hall enables it to run on a quarter of the energy consumed by a typical high specification office building. This is achieved not only through the use of ecologically sound, passive environmental control systems, but also through the shape and alignment of the building. The building's form and geometry has been generated as result of thorough scientific analysis, aiming to reduce both solar gain and heat loss via the building's skin.

Minimising the surface area of the building results in maximum efficiency in energy terms. The building's form is derived from a sphere, which has approximately 25 per cent less surface area than a cube of the same volume. The building leans back towards the south, where floor plates are stepped inwards from top to bottom, providing natural shading from the most intense direct sunlight.

The building is naturally ventilated, with openable windows in all office spaces. Heat generated by computers and lights is recycled. The deep-plan floors allow for the collection of heat at the building's core, which can then be redirected to its periphery. The combination of all these energy saving systems means that there is no need for chillers in the building.

Electrical consumption is reduced by avoiding refrigeration and using cold ground water to air-condition the building. The water is extracted from the water table beneath London through two bore holes and used to cool the building and then used in toilets and for irrigation savings on mains water.

In order to reduce the building's electrical consumption further, in 2007 solar panels are being installed on the roof of the building, to allow City Hall to generate its own solar power.

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