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Green and warm: The car park championing renewable energy

A 285-space car park may not seem an obvious place to champion renewable energy, but the designers of new office complex in Bedfordshire have used this space to house a state-of-the-art energy efficient heating system.

Materials giant Hanson wantedthe new base for its contracting arm to exude green credentials and to surpass current government guidelines on CO2 emissions.

Its 6,000m2 Kimberley complex close to the village of Stewartby appears to have exceeded expectations after receiving an Excellent BREEAM rating and an energy efficiency rating of B. In fact, the building is 30% more efficient than a typical new build and will save Hanson 42% in annual running costs.

The key to these huge savings is the project’s subterranean heating/cooling system, which uses five 130kW ground source heat pumps that run off the system to supply the demands of the entire building.

Lake water is fed through ground source heat pumps

Lake water is fed through ground source heat pumps

A traditional approach would have landed the firm with an energy bill of around £70,000 − but by linking a new sustainable drainage (SuDS) network to the geothermal system the bill is now about £4,800.

Architects TP Bennett, and Scott Wilson highways engineer, Geoff Arnold, tasked the Hanson Formpave design team with creating a paving and geothermal energy system that would work across such a vast site and utilise the natural benefits of the surroundings − the lakes to the left of the car park.

“We had to base the construction depth of the car park on heating capacity rather than a general construction formula”

Geoff Arnold, Scott Wilson

“Rather than simply store all the water, attenuate and release the clean water into the lakes and drainage systems in a controlled manner, our standard Aquaflow sub-base was modified to suit this particular application”, says Hanson Formpave renewables manager Roger Garrett.

“At a reduced level, an impermeable welded membrane was laid, creating a tanked reservoir area ensuring that the slinky pipes used in the ground source heat pumps process are constantly immersed in water. We had to base the construction depth of the car park on heating capacity rather than a general construction formula,” adds Arnold.

“With the Formpave team, we were able to fully utilise the space as well as reduce excavation costs, as it wasn’t necessary to excavate additional areas to install the slinky pipes − we simply used the base of the car park. With frost penetrating the ground up to 450mm deep we had to lay the pipes at 700mm depth to ensure that they didn’t freeze.

The headquarters has an Excellent Breem rating

The headquarters has an Excellent Breem rating

“This is in contrast to a typical car park excavation depth of 300mm. With the pipes 1m apart you can begin to appreciate the scale of the geothermal solution,” he says.

The slinky pipes are sat within 200mm of permanently saturated stone, with any overflow directed into the lake. The wet environment allows a better heat exchange, with the pipes needing the difference in temperature to maintain an optimum level of performance.

“We also had to ensure that the base was flat so that the water would always remain at its 200mm peak,” he adds.

Project manager on the job, Form 4 managing director Andy Szymanski says the scheme sets the standard.”Hanson Formpave has been able to ensure that the building and its occupants will make a saving in excess of 26% in CO2 emissions and of at least 42% in annual fuel costs.

“This solution offers pay back within five to six years. Kimberley is a perfect prototype for the future and sets the bar for building and construction in Britain for the next 10 years and beyond.”

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