Police source

The rise in demand and legislation for energy efficient buildings is bringing a raft of sustainable solutions to the fore. One of these, ground source heating and cooling, is being applied at Gloucestershire Police’s new £19 million headquarters and training facility.

The police force commissioned the four-storey, 8500 m2 building under a 30-year Private Finance Initiative (pfi) agreement. A key objective of the scheme was to achieve an Excellent BREEAM rating and an energy efficient and environmentally sustainable solution to the building’s heating and cooling needs.

One further objective meant a preference for natural ventilation was not possible. The client wanted full control of internal summer temperatures. M&E consultant McBains Cooper’s director of engineering Anthony Coumidis explains: “The challenge was the objective for an environmental building, while wanting heating and cooling to control the maximum temperatures in the spaces – these are two conflicting parameters.”

A grounded solution

The consultant proposed a heatpump solution using ground source energy as an alternative to a conventional boiler and chiller system. “We looked at geothermal as it allowed us to combine with air conditioning,” explains Coumidis. The system involves extracting the natural heat deep in the ground by sinking boreholes and pumping through treated water in a closed loop pipe network.

The installation was carried out by specialist contractor Geothermal Heating. It was the first part of the project to be carried out and was completed within three months of work starting on site. The site layout contributed to the decision for the early installation of the geothermal network. “It was a large site, so the main contractor could split it into areas of working: inside the building and the piling area. There was not much interface between the building and the geothermal system headers,” explains Coumidis. Once the system was complete the area was covered and site cabins erected for the building workforce.

Within the building the system will serve a ground floor underfloor heating and cooling system, plus fan coil air conditioning throughout the offices. The building will have a high element of IT use and heat from this will be recovered by the heat pump system and distributed to areas where it is needed or stored in the borehole for later use.

The heat pumps will also preheat the domestic hot water, which is a significant proportion of the overall load as the catering department will produce around 800 meals every day.

Reaping the benefits

The choice of system has brought several benefits to the project and with low maintenance needs, this should continue.

Once in operation it is estimated that the system will achieve energy savings for heating and cooling of 30-40% compared to a conventional air conditioning system. Combined with other energy efficiency measures such as solar shading and high thermal building fabric, it has an expected carbon rating of 13·5 kgC/m2/y, 5 kgC/m2/y lower than a comparable air conditioned building.

The client has more usable floor space as fewer and smaller plantrooms were needed. Also, maintenance costs will be lower than that of a conventional boiler system, with the savings rising the longer the system is in use.

Geothermal solutions are becoming more popular, but their application must be considered carefully. What made the solution possible here was the size of the scheme and the possibility to account for life cycle costs. Coumidis expands: “The fact that it was a PFI scheme, not a speculative building that the developer wanted an immediate payback on, meant we could talk long-term about the paybacks. The payback is seven to eight years; after this there is a considerable savings over the remainder of the time.”