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Green giant

Britain's largest court complex to be built for over a century is set to be judged as much on its sustainability record as its facilities. David Hayward reports.

'Wind scoops', 'environmental veils' and 'solar chimneys' are not terms civil engineers readily recognise.

But they will be soon.

Sustainability is now rmly entrenched in the construction process from conceptual design to final t out.

This is especially so in the 'internal environment control' sector where another buzz word - carbon footprint - can most be inuenced by engineers.

Manchester's innovative 16 storey Civil Justice Centre, housing 47 courtrooms and now nearing structural completion, boasts all these dictionary newcomers as it strives to minimise its impact on the environment.

'By maximising the use of natural light, fresh air, sun and groundwater we aim to reduce the building's carbon dioxide emissions by around 540t every year, ' claims Mike Still, associate with consultant Mott MacDonald.

'This should save the client at least £1.6M in energy costs over 25 years.' The result of an intense architect-led design competition, this futuristic looking composite steel and concrete building is seemingly pioneering every natural environment aid on the market. Its four dozen courtrooms, most of them large internal rooms clustered around the building's central core, will - in part - be ventilated with outside air ducted through the building.

They will be lit by natural daylight, routed roughly the same way; warmed by the greenhouse effect of a massive double-skinned glass atrium wall and cooled with the help of groundwater abstracted from 100m deep boreholes.

'It is the most highly integrated design we have worked on; coordinating environmental systems into the structure, architecture and services, ' says Still. 'The whole building needed advanced three dimensional modelling for energy, daylight and airow.' Visually, the £160M structure could be described as a stunning representation of what it contains.

Randomly protruding 'fingers', cantilevered out from each end, contain the larger courtrooms.

Their positioning is supposed to resemble the 'rising steps to justice'.

Admitting the whole design to be heavily 'architecture led', the consultant's engineers remain too polite to describe the structural form as a nightmare. But into its cantilevered maze of glass, steel and concrete, the designers had to route in an equally complex network of ducting, shafts and internal glazing.

Through these, engineers had to feed the usual electrical services as well as natural light and air.

Analysis was eased only by the advantage of Mott MacDonald being consultant for the total design - structural, mechanical, environmental and electrical.

The slim, 35m wide tower block is most easily explained as a series of vertical slices bringing public and court ofcials together. The structure's western face boasts Europe's largest hung glass wall, forming the outer double-glazed side of the 11 storey, 60m high atrium into which the public enter the building.

This atrium is interrupted only by a series of 16 randomly positioned 'pods' protruding from the main structure and spanning as far as the glass wall.

A central slipformed concrete core, with its lifts and stairs, links the concourse with courtrooms located within the heart of the building. Piled on top of each other, these large open span rooms average four per floor, with some cantilevering haphazardly out from the building's extremities as enormous glass ngers.

Finally, external full height aluminium sheeting, bracketed 600mm out from the main building frame, provides an 'environmental veil' on the building's eastern face.

Prime aim of the environment brief is to ventilate, light, heat and cool as many of the building's 1,000 rooms as possible - notably the bank of inner courtrooms - by routing in fresh air and natural light from outside.

These supplement - but do not totally replace - conventional air conditioning, heating and lighting.

Outside air is fed, at varying levels, into the building's west side, which faces the prevailing wind. It enters through 20 narrow, 7m long intake vents called wind scoops, located in solid wall areas at either end of the glass atrium cladding.

The fresh air is routed inwards and upwards, through shafts and ducts, to ow through the courtrooms and outside again from the building's eastern side.

Acoustic dampers reduce wind noise, while the wind scoops are sited a whole oor beneath the courtrooms they supply to ensure wind noise does not disrupt court proceedings.

Natural air ow is expected to reduce air conditioning use by at least 25%.

'Captured' daylight follows a similar path. Angled light shelves in the environmental veil direct light to main windows, increasing its intensity by about 15%.

Use of this channelled natural light means that rooms should need only 1kW of supplementary electric lighting, triggered by light sensors.

Summer time cooling is boosted by the sun-shielding effect of the perforated environmental veil, and by opening upper and lower vents in the enormous double-skinned atrium glass wall.

Further cooling comes from 12°C groundwater which will be pumped from deep boreholes up to the building's heat exchangers.

Here, the water absorbs some of the heat from incoming air before it circulates up through the building. Water ows out at about 28°C into the nearby River Irwell.

Winter heating is supplemented by the greenhouse effect on the 63m long atrium glass wall with its 6,200 panels. Shielding by the environmental veil, on the other side, helps to minimise heat loss, although engineers concede gaswarmed underoor heating will still be needed.

'We are aiming at reducing overall energy consumption by around 20%, compared to an equivalent air conditioned ofce of this size' concludes Still, adding: 'In a carbon footprint saving analogy, that equates to either planting 830 new trees or removing 135 cars from our roads every year.'

Complex and exacting The cutting edge design of architect Denton Corker Marshall for Manchester's new Civil Justice Centre is matched by its exacting engineering. 'This building demands one of the most complex structural designs we've been involved with, ' says Mark Thompson, associate structural engineer for consultant Mott MacDonald.

Behind this statement lie the calculations to accommodate substantial tension and compressive forces generated by the 21 cantilevering courtrooms. Bridge engineering technology was also needed to damp the vibration generated by the footsteps of people using the large open span oor spaces.

Demand from the building's tenant, the Department of Constitutional Affairs, that their court hearings should not be disturbed by surrounding ofce noise, results in stringent damping measures. The 100m tall building which, for at least 25 years, will house 47 courtrooms dealing with everything from High Court cases to family disputes, has been designed for maximum exibility.

Structural spans of 10.5m allow extensive internal partitioning for future reconguration of ofce space.

Main contractor Bovis Lend Lease remains on schedule for completing its £113M design and build contract by next spring.

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