With a ground source heat pump you can expect around 400% efficiency average through the year.
A ground source heat pump is able to produce a more constant level of heat than an air source heat pump i.e more heat in the winter. If you think about it the temperature around 1m down in the ground varies a lot less than the air temperature. The heat is transferred from the pipes in the ground to a heat store and then used to run the heating system and provide hot water.
Customers weighing up both options need to bear in mind the cost of excavations or bore holing, which are very variable depending on soil or ground structure. The best soil conditions for laying ground collectors is wet clay which will require many less metres of ground loop compared to dry sand.
Ground source heat pumps are ideal for new builds or barn conversions with enough land, they can also be a suitable option for ‘retrofit’ and systems can be designed with radiators appropriately sized for cooler water. For example R A Brown Heating have designed and installed one system for a converted watermill which was not undergoing renovation using the river as the heat source. Another retrofit system was designed for a fairly modern property with a large clear area of garden available for trenching.