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Innovate Green office, Thorpe Park, Leeds

A commercial building in Leeds has been awarded the highest ever BREEAM rating - 87.55 per cent - by utilising the high thermal mass of structural hollowcore concrete.

A sustainable wonder

The Innovate Green office, at Thorpe Park in Leeds, at first glance does not look particularly green. There are no windmills or solar panels. Indeed, it even has mechanical ventilation. Yet, the building emits 80 per cent less CO2 than a typical conventionally air-conditioned office, producing only 22kg of carbon dioxide per m2 per year. This equates to a saving of 350 tonnes of CO2 a year.

The design and construction approach developed by the project team was based on harnessing 'sustainable first principles' rather than adding renewable energy systems to a conventional building design. An engineering-led exercise produced an environmentally and commercially sustainable prototype building design with the sustainability credentials of each element being considered in conjunction with the client's need for flexible, commercially viable office space.

The building services were designed to be low carbon with low energy lighting and heating, cooling and electricity tri-generation provided by a 30kWe baseload CHP and matched absorption chiller. However it is the passive design features that makes this building excel.

The concrete structure plays a key role in the environmental performance, with the whole building designed as a thermal store. The structural frame consists of load bearing precast wall panels, precast floor planks and a single, central column line. The concrete incorporates fly ash secondary cementitious material, Lytag aggregates and recycled reinforcement.

Thermal mass

The concrete structure is externally insulated to substantially exceed the requirements of Part L at 0.15W/m2°C and exposed internally allowing its high thermal mass to regulate the internal environment. The floor and roof planks are used as Termodeck to further increase the thermal mass. In the Termodeck system the hollow cores of the precast planks are cross connected internally to create a serpentine labyrinth through which the supply air is passed. This additional contact between the environmental air and the interior of the floor planks engages virtually the entire mass of the concrete, not just that exposed at the external surfaces.

With the insulation levels achieved; the heat loss is reduced to a point where the internal gains provide the majority of useful heat. The building is mechanically ventilated and heat recovery AHUs collect the heat gains from people and computers and store the energy in the Termodeck for later beneficial re-use. Summer cooling 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.

Drainage and water

A vacuum drainage system utilises harvested rainwater for flushing the toilets. This virtually eliminates use of treated mains water to convey sewage. The overall volume of sewage discharged from the building is reduced by 75 per cent.While the provision of permeable paving and a natural wetland area prevents stormwater flooding.

Summary

This is a speculative office that provides real sustainability using existing and readily-available construction techniques and technology. Its success is due to the consideration given to the structural and building elements as an holistic, sustainable whole.