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Gatwick and Stansted satellite buildings

Focusing on carbon dioxide emissions rather than straight energy consumption was central to the design of two new 'satellite' buildings at Gatwick and Stansted airports.

A third satellite with 11 new aircraft gates is being added to the Stansted terminal, while Gatwick Pier 120 is to have eight extra gates serving 16 planes.

On both projects, energy consumption reductions exceeded the 20% target set by the Government following the Kyoto Earth Summit in 1997. Measured against BAA's best performing existing satellite, Stansted's new facility surpassed it by 22% and Gatwick's by 23%.

BAA appointed consultant WSP Environmental to the project team to develop a way to use CO 2rather than straight energy use as a key performance indicator for the global warming impact of buildings. At Stansted a matrix evaluation procedure was devised to balance capital cost, lifetime costings and environmental impact of different design elements. The study has helped BAA develop a new method for measuring energy performance, says Peter Sharrat, sustainability director at WSP Environmental.

'Which factors you concentrate on are subtly shifted by the switch from measuring straight energy consumption to a CO 2measure, ' he says. 'Gas derived energy produces 0.2g of CO 2per kW hour and electricity 0.44g/ kWh. It makes better sense to cut lighting, for example, than it does to cut heating.'

Sharrat explains that cutting energy use was difficult because the buildings are constrained by performance criteria and their orientation. The Stansted satellite 'has to match the existing satellites in elevation and their east-west orientation. They are completely glazed and so must this one be. And you are not allowed to compromise the passenger experience and views out from the airport'.

The task of reducing energy consumption was further complicated by demands for capital savings, savings in running cost, and that future modifications should be as cheap as possible.

Natural ventilation was ruled out because of the aggressive airfield environment. Energy saving measures examined included insulation to reduce heat loss and solar gain, shading, low transmission glazing and improving the efficiency of power use.

BAA was asked to consider whether it could restrict electricity demand within its usually brightly lit retail sector. The study questioned whether better use could be made of daylight without increasing solar gain, whether cooling was needed at all and heating was necessary at night. It also looked at using early morning crowds to boost ambient temperature naturally.

Fluctuations in passenger numbers and long term increases in passenger use ruled out dependence on natural cooling or heating. Fixed external shading and low transmission glazing were too expensive. Skylights did not produce significant daylight improvement.

But daylight controls with dimmers meant that electricity consumption could be reduced when natural light levels were high. An integrated approach to energy use removed areas where lighting was used inefficiently. Uvalues for opaque wall elements were improved and the building volume was reduced to minimise the heating and cooling needed.

Lessons learned at Stansted were swiftly transferred to Gatwick, and modified to suit the design.

Buildings consume 50% of all energy used in European countries. It is intended that the emissions profile of the new structures will contribute not only to BAA's environmental performance but will be an asset to the UK in the emerging global carbon trading market - countries achieving low emissions will be able to sell surplus 'clean air' quotas to heavy polluters. And, in the short term, reducing energy consumption will offer BAA savings when the climate change levy, penalising high energy consumers, is introduced next month.

Project team WSP Environmental Pascall & Watson - Architects (Stansted) GNW architects (Gatwick) BAA

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