Heat pumps

There are three main types of heat pump, air source, ground source and water source. Click on the menu options above to see the detail pages.

Air source heat pumps are sometimes called air/water heat pumps, they extract heat from the air and heat up water.

Ground source heat pumps are sometimes called brine/air heat pumps, they extract heat from the ground and heat the water they do not actually use brine, this name comes from the German word for the heat transfer liquid they use in the ground loop pipes.

Water source heat pumps are sometimes called water/water heat pumps and they extract heat from a river or lake and put it into the heating system water, they are less common and the systems are generally more complex than air source and ground source heat pumps.

All types of heat pump are a viable, highly energy efficient option for central heating and provision of hot water in this country, but they do require a slightly different approach to setting up the system.

Their efficiency is measure by their coefficient of performance (COP) This relates to how much heat energy they give out for each kilowatt of electricity they use.

Air source heat pumps have the lowest COP because they are extracting heat from  the air, the lower the air temperature, the less efficient they are.  Generally they stop operating at around -20 Celsius .  The annual COP of an average air source heat pump in the UK is around 2.5 to 2.8.  This means that over the year, for every kilowatt of electricity they use, they generate 2.5 to 2.8 kilowatts of heat.

Ground source heat pumps are more efficient than air source units because the ground temperature is more constant throughout the year.  The installation cost is generally higher than air source because of the work involved in putting the pipes in the ground.  The COP of a ground source heat pump in the UK is between 3.5 and 4.5 depending upon the type of ground (how wet it is) and whether the ground loop is laid as a horizontal grid (cheaper) about 1.2 metres deep in the earth, or as vertical bore holes (dearer) which go between 50 and 100m metres deep. In the medium to long term the additional cost of fitting ground source heat pumps will be recovered over the life of the pump.

Water source heat pumps are the most efficient type, but they have inherent problems if the source of water is not free from contamination.  Often it is simpler to us a ground loop within the water source as it removes the problem of potential blockage or contamination of the heat  pump. They can however achieve COP’s of 5 or more in the right circumstances.

The type of heating system they are connected to, and how they connect to it is very important for the smooth and efficient operation of the heat pump.  The best form of heating is wet under-floor heating, with the heating pipes laid in a cement based screed.  Low temperature heat emitters such as fan coils or fan convectors are also very good.  Both these types of heating can also be used for cooling in the summer, either active and passive. Even if you have a standard system with ordinary panel radiators, a heat pump is still a viable option.