Breath of fresh air

Leeds City Office Park, which is being developed by British Gas Properties, is one of the first major low energy commercial properties in the country. It has achieved 'excellent status' under the Building Research Establishment's environmental audit scheme - BREEAM.

To achieve this, the building has incorporated a variety of features designed to satisfy the demand for low energy design and a naturally ventilated office space. There is no air conditioning but all offices will have fresh air circulating under a raised floor, into the offices and out through the atrium. Tilt and turn windows will give the tenants an extra dimension in controlling their own environment. Even the underground car park is cheap to run and more friendly to the environment than most. It is open sided and will not require any expensive ventilation.

Due for completion in August, the œ5.7 million phase A of the development is being built by construction managers Schal as a core and shell. The fit-out will be done either to a future tenant's specification, or to the developer's separate requirements.

The three-storey building consists of two wings divided by a central atrium overlooking what will soon be an attractive central landscaped area. This will be in stark contrast to the badly contaminated land which once covered the site. Situated close to the junction of the ends of the M1 and M621 on the edge of Leeds City centre, it is ideally positioned for access and amenities. But so was the gas-works which previously occupied the site for over 150 years.

'I think British Gas have shown a real commitment to dealing with the environmental issues of the site,' said John Bray, Schal's project manager. 'It is definitely marketing the development on its environmental appeal.' The site is now squeaky clean. Contractors, carrying out the decontamination of the site, completed the job as Schal arrived on site last September. In turn, Schal is carrying out the preparation of the site for the remaining two phases of the œ20 million development, which will go ahead once the success of the first phase has been assessed.

Phase A is sure to be popular with prospective tenants. The developer has certainly done its research on what tenants and their employees want in a building. The position of the building, in relation to the city centre, railway station and motorway access, is ideal. But it is the measures taken to ensure the comfort of the people using the building which will make it attractive. The lower running costs may also influence the people who will be paying the bills!

The central atrium is the core of this attractive building, and of the air circulation system which will keep the office workers comfortable. Filtered fresh air will be taken in at roof level and delivered, via ductwork running under the raised floors, through floor grilles into the office space. As it warms the air will rise, pass through the void above the suspended ceiling and into the atrium through voids in the troughs of the pre-cast floor units and the in-situ concrete beams.

The atrium walls are timber panelling with a mesh pattern at slab level, allowing the passage of the air. This controls the stack effect which will naturally take the air up to roof level. The roof of the atrium is glazed with vents which open automatically, allowing the air to be extracted. In winter the warm air at roof level will be ducted back to the air handling plant where it will be passed through a heat exchanger before being discharged to the atmosphere.

The glazed roof is silk screened to limit the degree of solar gain (an environmentally friendly greenhouse effect). These are also a feature on the upper sections of the glazing units which are integrated into the Italian manufactured cladding. On these units though, the blinds will be powered by the building's occupants. There were some initial manufacturing problems in Italy with achieving the edge detail of the glass. This set the programme of the external envelope back by several weeks, but John Bray is confident of recovering this before completion is due in August.

To provide extra help with controlling the solar gain there is a natural anodised aluminium sunscreen on all elevations of the building. This consists of an aluminium mesh and framework which will also act as an access for maintenance.

But if, despite these measures, further cooling is required by the tenants, extra ductwork capacity has been installed and space allowed in the plant room for cooling equipment. Heating will be provided by steel wall panel radiators with thermostatic valves controlling groups of radiators.

However, this variety of measures will probably have its biggest impact in perhaps the most important place - the tenant companies' final accounts. Energy costs for Leeds City Office Park are predicted to be around a quarter of those for a typical air-conditioned office building.