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Something in the air

Environmental modelling

New environmental legislation is set to change the way buildings are designed. London's Swiss Re tower offers pointers to the future, explains Lisa Russell.

Buildings increasingly share a bond with Formula 1 cars - at least at the design stage. Both depend on the same sophisticated air flow simulations to determine their performance.

Environmental modelling is becoming as integral as CAD in the design of leading-edge buildings, believes divisional director of environmental modelling at Hilson Moran, Matt Kitson. He believes three factors are driving this: faster hardware at lower cost, more stringent legislation and the desire of many architectural practices to use new forms, materials and designs.

One of the most striking results is Swiss Re's newly completed landmark headquarters at 30 St Mary Axe, London.

The 180m tall circular curving tower is being heralded for its progressive approach to environmental performance. It has been designed to use up to 50% less energy than conventional office blocks. Controlled opening of the windows will allow the air conditioning to be switched off for up to 40% of the year. 'You couldn't design a building like Swiss Re without the input of environmental modelling, ' says Kitson. 'You wouldn't get the full potential out of it.'

Swiss Re's decision to commission an environmentally progressive building long predates recent and planned regulations. But many of the approaches are set to become relevant even in more ordinary buildings.

Further changes to the Building Regulations are ahead, driven by EU legislation on building performance energy labelling, due to come into force in 2006. Every building frequented by the public - new and existing alike - will need to be rated, explains Kitson, just like the white goods sold by electrical retailers. This will increase environmental awareness, he believes.

Hilson Moran Partnership's role on the Swiss Re project has spanned more than five years of close work with other members of the team which includes architect Foster & Partners, structural engineer Arup and shell and core main contractor Skanska.

One of the keys to the energyefficient design was the adoption of triangular light wells which spiral up the building, letting natural light penetrate deep into the interior.

These also play a crucial part in the natural ventilation.

'They are the lungs of the building, ' says Kitson. The office space opens to the light wells via balconies; and the wells have external motorised windows to let in fresh air. 'The light wells also serve as a buffer zone, slowing down the air coming in, ' says Kitson.

Environmental modelling was instrumental both in the placement of the light wells and in ensuring that partitioning did not break down the natural ventilation, explains Kitson.

Other models looked at lighting and the effect on passing pedestrians - the aerodynamic design reduces downdraughts.

Fourteen faþade options were tested using computational fluid dynamics (CFD) and dynamic thermal modelling. The final solution included an internallyventilated cladding system with a double-glazed outer skin, an inner screen with inter-cavity blinds and a rotating solar-tracking shading device inside the summit's glass dome.

Simulations had to be high quality from the outset, as early decisions have a huge bearing on the design. 'There is a whole array of suites of software that we used to get a better understanding of the complex space and how it is going to function, ' says Kitson. The modelling often used the same software as Formula 1 cars. 'One of the codes we used for the CFD modelling was Fluent.'

CFD techniques are well established, but analysis with toplevel programs takes considerable computing power. Even today's desktop computers need help to handle the computations. 'We run the simulations over clusters of machines daisy-chained together, ' says Kitson. 'When you add them all together, it's like a Pentium 30,000.'

These techniques will be used more frequently, believes Kitson, as could the environmental solutions. Swiss Re is one of very few 'blue chip' high rise UK offices to have opening windows.

Any building can make an environmental statement, says Kitson, 'but Swiss Re makes quite a powerful one'. It is becoming acknowledged as a benchmark of what is possible, he believes.

INFOPLUS www.30stmaryaxe. com www. hilsonmoran.co.uk

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