Leeds office building sets new high BREEAM rating

Published:  11 November, 2007

Britain’s new record holder of the highest BREEAM rating is this office building at Leeds. (Photo: Robert Greshoff)

Only proven technologies are used in a new commercial office building in Leeds, but the way they have been brought together sets a new landmark for energy efficiency in buildings.

It cannot be long before a building in the UK achieves a BREEAM (Building Research Establishment Environmental Assessment Method) score of 90% or more. A new record has been set with the completion of a new commercial office building in Leeds for Innovate Properties. Now open for business, it has a BREEAM score of 87.55% — a sizable improvement on the previous highest score of 84.01% for the headquarters of Scottish Natural Heritage in Inverness. Another similar improvement will smash through the 90% barrier.

This £5.5 million, 4500 m2 serviced office building was designed by Rio Architects with environmental engineer King Shaw Associates. It features many novel techniques to reduce energy consumption and carbon-dioxide emissions — both during construction and in use.

Engineering led

An engineering-led exercise produced an environmentally and commercially sustainable prototype building design, which was applied to the specific plot on Thorpe Park, a business park on the outskirts of Leeds. Yorkshire Forward worked with Innovate Property to fund part of the cost of prototyping sustainable construction methods.

The team’s approach was to examine each element from first principles and assess its benefits to the overall building performance, rather than bolting sustainable features onto a conventional design. The result was a design using proven technologies, assembled to provide an optimum solution.

Carbon-dioxide emissions from this comfort-cooled building are substantially lower than typical air-conditioned offices, and on a par with the best naturally ventilated buildings. The predicted carbon-dioxide emissions of 22 kg/m2 per year are over 80% lower than a typical office building — a saving of over 350 t per year.

The savings in energy consumption are about £14/m2 a year. This figure compares with expected rental returns of £130 to £160/m2 — thereby making a significant contribution to Innovate’s business profitability.

As the photograph shows , there are two offset office wings separated by a narrow glazed street. The concrete structure is rendered white and externally insulated to substantially exceed the requirements of Part L at 0.15 W/m2K and exposed internally to give a high thermal mass.

There are no windows on the north and south facades, minimising thermal loss and solar gain. Windows on the east side enable the building to benefit from early-morning passive solar heating. Vertical fins between each modular window unit provide solar shading and enliven the facade.

The offices average a daylight factor of 4.5%, so electric lighting is required for only 20% of the working year.

Building-services plant is housed at roof level in elliptically shaped fibre-reinforced polymer shrouds.

Thermal store

The whole building is designed as a thermal store, with the floor and roof slabs of TermoDeck to further increase the thermal mass and enable its use to be maximised. The insulation levels reduce heat loss so much that internal gains provide most of the useful heat.

A 30 kW CHP trigeneration unit provides electricity, heating and cooling, with a matched absorption chiller.

The building is mechanically ventilated, and heat-recovery air-handling units from Flakt Woods recover heat gains from people and computers and store the energy in the TermoDeck for reusing later.

Cooling in summer is provided by a combination of passive night cooling and active cooling from the chiller, using the TermoDeck as a thermal store in a strategy similar to ice storage.

Doug King, principal, King Shaw Associates, explains, ‘The choice of TermoDeck was key for this scheme. The developer did not want to rely on natural ventilation alone as it thought that the market risk would be too great. The building was therefore designed as a giant heat store, with a super-insulated concrete frame and TermoDeck to provide sufficient thermal mass to minimise the demands on mechanical plant.

Geoff Russell-Smith, general manager of TermoDeck, adds, ‘In recent years, natural ventilation has been seen as the alternative to refrigerant-based air conditioning, but cannot guarantee consistent air flow, good air quality and comfort levels. With severe climatic changes forecast, the TermoDeck system really comes into its own as a viable low-energy option to effectively future-proof new buildings.’

Thermal wheels

The Flakt Woods EC2000 air-handling units have thermal wheels that can recover up to 90% of the energy in the extract air; a typical figure is 75 to 85%. These AHUs have heating and cooling coils, low set-point face velocity fans and pre-wired inverters. Ventilation is supplied via the TermoDeck hollow-core concrete slabs, so that both heat and ‘coolth’ can be stored.

The finishing touches are provided by rainwater harvesting, coupled with vacuum drainage, which virtually eliminates the use of mains water for sewage and reduces the overall volume of sewage discharged by 75%.

Reviewing the project, Stephen Dargavel, joint managing director of Innovate Holdings, says, ‘We were stepping into the unknown when we initiated the development of Innovate Office Leeds. However, the fantastic score given to use by the Building Research Establishment has reinforced our vision of combining cutting-edge environmental considerations with a business environment that is second to none.’

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