A ground-breaking system

Think of a Private Finance Initiative (PFI) and it’s usually conventional, tried and tested. This is hardly surprising, considering PFI consortia must finance a facility and run it for 30 years.

The Reliance HBOS Consortium is breaking this mould, however. It is behind a daring new building that boasts the UK’s largest geothermal heating system: the £20m Gloucestershire Police HQ at Quedgeley, which houses 800 people. The heating system in this building aims to enable the police to cut carbon emissions and the costs of heating and cooling.

As multi-disciplinary consultants to Reliance, McBains Cooper’s brief was to provide an environmentally friendly, low- energy building with a BREEAM rating of ‘Excellent’. The facility also needed comfortable internal room temperatures throughout the year.

Using natural ventilation would have risked high temperatures during the summer, leading to penalties in the PFI contract. To guarantee low temperatures, air-conditioning was needed, but that was not an environmentally friendly option. So a geothermal solution which used a reversible heat pump was deemed the only means to resolve such conflicting demands.

Initially, McBains Cooper had to persuade not only the Consortium of the benefits of the innovative technology, but also the police, the bank and even McBains Cooper’s own quantity surveyors.

Taking a 30-year view of the situation clinched the deal. Geothermal heat pump systems are more expensive to install than standard heating systems, but the lower running costs lead to short payback periods. The system will pay back in just over eight years, compared to a conventional system which uses a chiller and boiler.

So how does it work? Water circulates in a ground loop, based on 180 boreholes that are sunk 98m into the ground. The temperature of the earth remains constant all year round at about 13ºC; the water can be warmed up during winter and cooled down in summer.

This is a daring new building that boasts the UK’s largest geothermal heating system, which aims to enable police to cut carbon emissions

A heat pump transfers the small temperature rise within the groundwater loop to a higher temperature rise for the internal loop. The heat pumps can achieve a temperature range of up to 50ºC for heating and 7ºC for cooling.

The only energy that the system takes is electricity to power the compressor. Three- quarters of the building’s energy comes from the ground and is therefore free and clean energy.

The geothermal system should have significant environmental and cost benefits, as this type of system produces more energy than it consumes. A geothermal system will generally produce energy savings of up to 40% in comparison with a conventional air-conditioning system.

The building is expected to have a carbon rating of 13.5kg/C/m2/year, which is 5kgC/m2/year lower than a similar air-conditioned building.

We also predict significant savings of about 18% over the whole building life-cycle due to low maintenance, in comparison with a boiler/chiller system.

The system’s energy consumption is 6% below our declared target, and this should reduce even further as the building services are fine-tuned. (See graphs for energy predictions versus actual use for the first 11 months of operation.) This project provides a blueprint for other schemes, even risk-averse PFI consortia.