Gerald and Sue Hartley have recently moved to New Moreton Farm near Gloucester, and wanted to make their old farmhouse as sustainable as possible in its energy needs. They have a long-standing interest in the environment, and renovating their home has given them the opportunity to install a ‘trench' type ground source heat pump. With the help of solar panels, this should provide all the hot water and space heating demands for the house throughout the year.
A ground source heat pump collects the solar energy stored naturally in the ground and transfers it via a network of pipes to the building's heating system. The pipes are connected through a water circulating pump (the ‘source' pump) to the evaporator of a vapour compression refrigeration unit (the ‘heat' pump).
A water and antifreeze mixture, which the heat pump attempts to cool to a temperature of around 2 celsius, is circulated within the ground loop by the source pump, whenever the building's thermostat senses a demand for heat. The ground holds a stable heat all year round of between 8-14 celsius, and the 10 celsius or so difference between the surrounding earth and the loop causes energy to flow from the ground into the loop, warming the source water for the heat pump.
The heat pump's condenser is fitted into the heating system's primary pipe work and takes the place of a boiler in a conventional system. It heats the water to temperatures suitable for a domestic heating system.
Strictly speaking, a GSHP is not a renewable energy technology as electricity is required to drive it. But it is highly efficient, and for every unit of electrical power needed to extract the heat, 3-4 units of useable heat can be obtained. Switching to an Economy 7 or 10 electricity tariff ensures maximum financial savings. With a properly sized system, significant reductions in overall CO2 emissions can be achieved.
Condenser and water storage tank for GSHP
A big advantage of the latest GSHP systems is that they can be used in reverse during the hotter summer months to act as cooling units, extracting the heat from inside a house and ‘dumping' it into the ground.
The Hartleys have insulated their home to the highest possible standards to ensure their energy demand will be as low as possible. They are laying underfloor heating at ground and upstairs level, and it is vital that the floor is well insulated, as well as the walls and ceilings. Although standard radiators can be used with a GSHP, the water is at a lower heat than in a conventional boiler system, making it particularly suitable for underfloor heating.
The pipe work for a GSHP can be in either a deep vertical borehole of about 75m in depth, or in a trench system of about 1.5 m depth. The Hartleys have installed the trench-type system.
The pipes in a trench system are generally curled around in a coil shape, but at New Moreton Farm the pipes have been laid lengthways in the trenches to minimise heat loss, requiring additional trenches to house the 500m of pipe work needed. The pipes for ground source heat pumps need to be covered by a generous layer of sand, an additional cost.
Digging the trenches has been a family affair. Gerald and Sue's daughter, her partner and friends have all got involved. Without their help, a 5-man team would have been needed for about 2 weeks to dig trenches, lay the 40mm black polypropylene pipes and operate the two large diggers needed to complete the job.
The vertical borehole-type ground source heat pump is more practical for those who don't have enough land to dig a network of trenches. Drilling equipment needs to be brought in to drill the borehole to the required depth. Stroud District Council has recently installed seven borehole-type ground source heat pumps at off-gas council homes in Coaley. These have replaced a variety of heating options such as solid fuel stoves, night storage heaters and open fires. The Council are monitoring performance carefully to see how economical and effective they are.
Ground Source Heat Pumps are expensive to install. The Hartleys estimate that their particular installation will cost roughly £15,000, excluding the digging costs of about £5,000. However, Gerald and Sue feel that this is a price worth paying. “Once the ground source heat pump is up and running it should be reliable, economical to run and require little or no maintenance for at least 20 years. We hope to be long gone by the time it starts to play up!”
Grants available
There is money available for domestic renewable technologies through the government's Low Carbon Buildings Grant. An approved installer from the list on their website will need to be used. As the grant is reviewed regularly, it is best to check the website at the time of application to find out how much is available for GSHP. www.lowcarbonbuildings.org.uk
Stroud District Council has a grant of £500, available through their WISE Homes grant, to encourage local householders to install renewable technologies in their homes. This money is available in addition to any money received via the Low Carbon Buildings Grant. Go to www.stroud.gov.uk and click on the environment tab on the homepage.
Ground Source Heat Pump Installers in the Stroud area.
AJ Buchan near Tetbury (with showroom)
T. 01285 841 466
Elite Efficient Energy
Contact: David Mark 01453 755677
E.elite.heating@btconnect.com
W.www.eliteefficientenergy.co.uk
Ecovision Systems
Barley Court
Highgrove Estate
Tetbury
Gloucestershire
GL8 8TQ
T. 0845 003 8002
F. 01666 505 080
E. enquiries@ecovisionsystems.co.uk
Website:
www.ecovision.co.uk
