Ground source heat pump
Ground source heat pumps use pipes that are buried underground to extract heat from the ground, which is then further heated and moved to the heating and hot water circuits of your property.
A mixture of water and antifreeze is circulated around a loop of pipe which is buried in your garden. Heat from the ground is absorbed into the fluid and then passes through a heat exchanger into the heat pump. Since the earth absorbs energy released from the sun, underground temperatures are constant. In the UK, the temperature of the earth a few metres below our feet remains at around 11°C.
The length of the pipe in the ground depends on the size of your property and the amount of heat you need. Longer loops can draw more heat from the ground, but need more space to be buried in. If space is limited, a vertical borehole can be drilled instead.
If you are considering installing a ground source heat pump you will need to seek advice on whether your property is suitable. You need to check if you have enough outdoor space to support the underground pipes and pump, and access for digging machinery.
Air source heat pump
Air source heat pumps look similar to air-conditioning units. They are less disruptive to install than ground source heat pumps and they are cheaper.
An air source heat pump extracts heat from the outside air in the same way that a fridge extracts heat from its inside. Heat from the air is absorbed at low temperature into a fluid. This fluid then passes through a compressor where its temperature is increased, and transfers its higher temperature heat to the heating and hot water circuits of your property.
An air source heat pump can get heat from the air even when the temperature is as low as -15°C.
Air source heat pumps are classified as either air-to-air or air-to-water depending on whether the heat distribution system in the building uses air or water. An air-to-water system distributes heat via your wet central heating system. An air-to-air system produces warm air which is circulated by fans to heat your property. It’s unlikely to provide you with hot water as well, but in the summer you can operate it in reverse and use it like an air-conditioning unit.