The ground source pipe is laid in a metre deep trench or lowered into the bore hole and is then filled with an antifreeze. The fluid picks up low level heat as it is pumped around the pipe. This is then fed into the heat exchanger in the heart pump where refrigerant gas passes across it in a sealed circuit. The gas is then compressed to concentrate the heat and pass it to the heat exchanger. Having passed its heat the gasses then goes through a decompression device so it can pick up heat all over again.

The fluid passing back into the ground loop may then be below freezing and as heat always passes from warm to cold it will pick up heat immediately it enters the ground or air. Where the flow and return pipes are run close together in the trench there is a chance that the colder pipe will pick up heat from the warmed pipe and take it back to the ground. The two pipes are both well insulated in the trench to prevent this unwanted transfer.

Given that heat pumps are little more than refrigerators with their door left open you may wonder why they cost several thousand pounds each. Undoubtedly as more competition enters the market the price will fall but a great deal of the cost is in the control systems which optimize performance to suit the heating load. The erratic weather in the British Isles means that from one day to another it is impossible to predict your heating requirements but at least the computer can work out how long a house takes to heat up from a given outside temperature. This interface is important because a heat pump working over time it is still costing you money even if it is less than a boiler. We also need to get used to the idea that our homes will feel more comfortable with a steady temperature rather than short sharp bursts of heat. It therefore follows that heat pumps are ideally suited to well insulated buildings.

Article links:

• TRIANCO ACTIVAIR - The best value air source heat pump we have found.
• GLEDHILL / MITSUBISHI
• NU-HEAT UNDERFLOOR HEATING SYSTEMS
• THE HEAT PUMP ASSOCIATION - The UK's leading authority on the use and benefits of heat pump technology.
• WORCESTER BOSCH - Manufacturer of the Greenstore ground source heat pump.