Ground source heat pumps are the most efficient type of heat pump. They work by installing pipes under the ground, filled with a refrigerant liquid. As the refrigerant liquid passes through the ground, it absorbs the grounds heat. Due to the ground maintaining a fairly constant 10C temperature, ground source heat pumps have a consistent efficiency all year round.
There are two methods for installing the pipes in the ground, or 'ground array'. Borehole systems involve drilling 80-100 meter vertical holes in the ground and lowering the pipes down. Whereas, horizontal systems involve digging 1 meter deep by 1 meter wide trenches horizontally across the ground and laying the pipes within the trenches - don't worry the ground will be re-turfed after!
Both types of ground array will have a small concrete unit built at surface level, which will house the manifold and other serviceable parts. Because of the cost of the ground array install, ground source heat pumps often cost around twice that of an air source heat pump, from £15,000 - £30,000. However the grants available are larger than for air source heat pumps.