Ground source heat pumps (GSHP) transfer heat from the ground into a building to provide space heating and to pre-heat domestic hot water. 

How it works.
There are three important elements to a GSHP:

1. The ground loop. This is comprised of lengths of pipe buried in the ground, either in a borehole, a horizontal trench or a slinky coil. The pipe is usually a closed circuit and is filled with a mixture of water and antifreeze, which is pumped round the pipe absorbing heat from the ground. 
2. A heat pump. This has three main parts:
   • The evaporator - (e.g. the squiggly thing in the cold part of your fridge) takes the heat from the water in the ground loop;
   • The compressor - (this is what makes the noise in a fridge) moves the refrigerant round the heat pump and compresses the gaseous refrigerant to the temperature needed for the heat distribution circuit;
   • The condenser - (the hot part at the back of your fridge) gives up heat to a hot water tank which feeds the distribution system.
     
     
3. Heat distribution system. The heat can be emitted by under floor heating or correctly sized radiators, for space heating and properly designed systems can also accommodate the hot water supply.

The efficiency of a GSHP system is measured by the coefficient of performance (CoP). This is the ratio of units of heat output for each unit of electricity used to drive the compressor and pump for the ground loop.  Typical CoPs range from 3 to 4 although some systems may produce a greater rate of efficiency.  The higher end of this range is when under floor heating is used because under floor heating can sufficiently heat a building at a lower temperature than a radiator.

What to keep in mind when considering a ground source heat pump.

• GSHPs can be used with radiators but under floor heating works better at lower temperatures.
• Is there space available for a trench or borehole to accommodate a ground loop?
• What fuel is being replaced? If it's electricity, oil, LPG or any other conventional fossil fuel the payback will be more favourable. Heat pumps are a good option where gas is unavailable.
• Want to be 100% renewable? 
  Buy green electricity or install a wind turbine (or solar PV) to generate electricity and power the compressor and pump – then you will be!
• Is the system for a new building development? Combining the installation with other building works can reduce costs.