Ground-breaking. Literally

How often in a career do you get the chance to work on a truly ground-breaking building? Once or twice? Probably never. So when Anthony Coumidis, a director of consultant McBains Cooper, sniffed an opportunity to make building services history, he wasn’t about to let it pass him by: “I wanted to do something different. I wanted to design something challenging.”

Coumidis, who heads up the firm’s engineering services business, is responsible for the design of the UK’s biggest ever geothermal heat pump, which will heat and cool Gloucestershire Constabulary’s new headquarters and training facility. It’s the first large-scale application of this technology in the UK, providing 646 kW of heating and 756 kW of cooling at peak for a building which will hold up to 400 people.

The geothermal heat pump uses the ground, which remains at a constant 13 degrees C all year round, as a sort of battery. In the winter the pump uses heat from the ground to heat the building and in the summer it discharges heat from the building into the ground.

Many would shy away from introducing technology untried on this scale, held back by concerns over professional indemnity and reputation. Not Coumidis. As one person on the project put it, “Anthony’s got guts”.

McBains Cooper is architectural, structural and M&E consultant for Gloucestershire FM Services, a consortium which is designing, building, financing and running the facility for the constabulary under a 30-year PFI deal. The 30-year view certainly helped the argument for geothermal heating; the system will pay back in just over eight years when compared with a conventional system using a chiller and boiler.

But there were still plenty of people to persuade: the banks’ consultants, the police authority’s consultants and McBains Cooper’s own quantity surveyors. When QSs don’t have any previous jobs on the database, it all comes down to trust, says Coumidis. He reckons this is one benefit to being in a multi-disciplinary practice: trust between departments is easier to establish. But it’s still his head on the block.

So how did Coumidis, together with Geothermal Heating (which is supplying and installing the system), get everybody on board? Coumidis’s enthusiasm and drive must have been an important factor. They modelled the building for heating, cooling and carbon emissions for both conventional and geothermal set-ups. And then they really got to work, performing presentation after presentation.

One difficulty is that there weren’t any similar projects in Europe. In the UK there are around 1,000 installations, but they are all domestic or small buildings. There was a visit to an office building in Holland that used an open loop system rather than a closed loop system, which is what the Gloucester project will have.

A closed loop system means water circulates in the ground within closed tubes. An open loop system takes and returns water from a lake or aquifer. It requires a suitable water body and a licence from the Environment Agency.

The £18m building, which should be finished by next October, is four storeys high. The ground floor, built around an internal street, will house a large IT room, sports hall, conference facilities, restaurant and lab areas. Above that are three layers of offices.

The constabulary wanted a building which would achieve an Excellent BREEAM rating -meaning it would have low carbon emissions. The client also asked for specific temperatures in some areas. The use of the geothermal heat pump contributes towards the BREEAM rating and allows the consortium to deliver ‘bonus’ cooling in some areas at no extra cost. The system can also redistribute the heat produced by the IT rooms to other parts of the building.

How does it work? The diagram (right) explains in detail. Put simply, water circulates in closed loops within 150 boreholes, sunk 98m into the ground. Because the temperature of the earth remains constant all year at about 13 degrees C, the circulating water can be warmed up in winter and cooled down in summer.

We’ve promoted the technology for years, trying to prove it’s a goer

Brian Davidson

A heat pump transfers the small temperature rise within the ground water loop to a higher temperature rise for the internal heating loop, in a process similar to that used in a fridge. The only energy it takes is electricity to power the compressor. The energy taken from the ground is around three times the energy required to compress the refrigerant, which means that three quarters of the energy has come from the ground and is therefore free, clean energy.

In summer the heat pump is reversed so that the water circulating in the boreholes is transferred to the ground, and stored there to be reused in winter. This means more energy can be extracted the following winter so that the returning water from the boreholes is warmer. This in turn makes the pump more efficient.

Digging for more

How many boreholes you will need depends on the geology of the ground. Geothermal Heating’s technical director Chris Davidson says that the strata can make a four-fold difference in cost. The ground at Gloucester is not a good conductor, so the boreholes have to be relatively far apart at 6.5m spacings.

Borehole installation needs a specialist firm. Gloucester Raeburn Drilling, a partner and shareholder in Geothermal Heating, did the work between July and October. On this site they were able to separate off the work area, drilling holes, inserting the polyethylene pipes in which the water will circulate and then filling up the holes with a conductive grout.

All the pipes have now been connected up to the building and pressurised, a process which required Raeburn to work closely with main contractor Britannia Construction so that the trench digging fitted in with other works. There will be no evidence of the borehole field when the project is finished, except a series of manhole covers in the car park. The next job, come May, will be connecting up the heat pumps.

Once the building is in operation, McBains Cooper will be able to monitor its performance to provide valuable evidence for future projects. It’s a prospect that excites Coumidis.

Already the Gloucester job has opened the door for geothermal on other projects. “We have been promoting the technology for three and a half years, trying to convince people that this is a real goer,” says chief executive Brian Davidson. A closed loop system will be used on a PFI hospital three times the size of the police HQ and Davidson is working on other projects too.

The changes to Part L and continued pressure on oil prices indicate there could be many more projects where geothermal fits the bill. Not all plots have enough space for car parks, so the next step is to build boreholes into the foundations.

Having pioneered the system in Gloucester, Coumidis and McBains Cooper hope they will be first in the queue for any new projects.