When planning to install a ground source heat pump, you should consider a few questions:
Is there access to the ground?
Most systems installed in the UK use heat collecting pipes (loops) buried in shallow trenches. You'll need to check that you have a large enough area of land to install the ground collector loops, especially if you need to heat a sizeable building. Otherwise, it's possible to place the heat collector in a vertical borehole, which only needs a limited surface area for access.
Is the building well-insulated?
As with any new heating system, it's important to make sure that no heat is wasted through poorly insulated walls, ceilings or floors. When planning to install any new heating system, it might be cheaper to add extra insulation first, in order to reduce the capital cost on installation and the running costs of using it.
How big a system do I need?
Once the heat loss through the fabric of the building is known, it's possible to calculate the maximum heat demand under typical winter weather conditions. This calculation will also consider whether domestic hot water (DHW) is to be provided either wholly or partially from the heat pump. This can then be converted to give the optimal size for the heat collector loops (whether in trenches or a borehole). The installer will also be able to advise whether the ground conditions will permit summer heat replenishment around the collector loops that will enable successful heat extraction in colder months for many years.
Ground source heat pumps tend to work most efficiently when raising water to a temperature around 40°C, and so are best matched to a wet underfloor heating system, although 'oversized' radiators can be used as an alternative. As it's not normally cheap to fit a wet underfloor heating system into an existing property, ground source heat pumps are most commonly installed into new properties. They can be installed in older buildings if attention is given to improving insulation and - if necessary - increasing the size of the heat emitters such as radiators.
The source of the heat collected by the ground loops is ultimately the sun's energy, that warms the surface of the earth and gets absorbed by the ground. The only conventional energy used in a ground source heat pump system is electricity for the pumps and compressors, which are needed to run the system. Typically, these use only a quarter as much energy as is released into the building in the form of heat so a ground source heat pump can be 300-400% efficient.
The performance of a ground source heat pump depends greatly on the quality of the design and installation. Maximum performance is achieved by matching the specification of the installation to the needs of the building and its use, and ensuring that a balance of heat exchange is maintained within the ground over the year in a sustainable way by utilising solar recharge of the ground.
More information is available via the Ground Source Heat Pump Association website.