Why ground source heat pumps?

Ground Source Heat Pumps (GSHP) are more efficient than an Air Source Heat pump.  The ground, from which they take their energy is a more stable source of energy than the air. 

The performance from a GSHP depends on the type of ground collector used to extract the energy.  There are four types of ground collector commonly used in the UK.  The average temperature of the water in the ground collector differs for each type.

Horizontal Loop ­– Pipes are laid about 1 metre below the surface in trenches.  Average water temperature 0oC – 10oC

Vertical Loop – Pipes are placed in bore holes at a depth of up to 100 metres.  Average water temperature 10oC

Pond Loop – Pipes are coiled up and placed in water (pond, lake or river).  Average water temperature 7oC

Open Loop – Fresh water is sucked in and discharged back in to a water course.  Average water temperature 8oC

How they work
A GSHP uses the variable energy found in the ground or water that the collector pipes are placed in.  Typical average UK winter ground temperatures tend to be around 4 or 5oC (horizontal loop).  The heat pump boosts this low energy via its refrigeration circuit to a usable level for the provision of heating and hot water for the home.

This works by taking advantage of the energy created when a refrigerant gas is compressed to a liquid.  The refrigerant is first passed through a heat exchanger where it is warmed by the ground collector water.  This heat exchanger is called the evaporator.  The now slightly warmed refrigerant gas is compressed to a liquid which dramatically increases the temperature of the refrigerant.  The hot refrigerant liquid is then passed through another heat exchanger which is then used to warm the system water (Underfloor Heating or Radiators).  This second heat exchanger is called the condenser. 

In order to start the cycle again, the refrigerant liquid must be converted back to a gas and this is done by the expansion valve.


How varying water temperatures affect the performance
The output from a GSHP is not fixed and it will vary depending on certain conditions.  The certified output of a GSHP is measured for a ground inlet temperature of 0oC and a heated water temperature of 35oC.  However, if the inlet temperature falls or the heating water temperature rises then the output of the GSHP will fall.
This is illustrated on the ground source heat pump power graph.

All Radiant Heat Pumps can be ordered in Heat and Cool models as required.  The cooling process simply reverses the refrigerant gas circuit.  This is ideal when summertime cooling is required.

We also have special models that capture the waste heat in cooling mode to heat the hot water tank.

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The power graph will show the amount of power in kilowatts that is available at a given source and heated water temperature. It is therefore easy to plot the output for any source temperature against any system flow temperature. It is part of the design tool used to specify the correct machine for any given application. Most manufacturers will provide these graphs to system designers.
Brine is the common term used to describe the fluid in a closed ground collector loop. This is typically a mixture of pure clean water and a glycol antifreeze.