Brookforge swimming pool engineers

Geothermal & Ground Source Heat Pumps

1. An Introduction

The Use of Ground Source / Geothermal Heat Pumps for Indoor Swimming Pools

The application of domestic ground source heat pumps, instead of fuel boilers, has recently become very popular and this technical paper has been produced to aid the general understanding of how such systems operate and what the implications / limitations are in respect of swimming pool applications :


Swimming PoolThe whole concept of a ground source heat pump is based on the fact that the temperature underground is generally constant at between around 8°C to 13°C in the UK and that this temperature can be up-graded, through the compression effect within a refrigeration heat pump, into a usable temperature for heating purposes.

The well known heat pump principle applies, in that the customer only pays for the energy consumed in mechanically operating the heat pump (which is, itself, fully utilised), whilst the customer does not pay for any of the heat absorbed from the ground.

For every 1.0 kW of 'paid' electrical energy which the heat pump consumes in it's mechanical operation, a total of 3.5 kW can typically be produced for the customer to use. This would frequently be expressed as a the 'coefficient of performance' or C.O.P. of '3.5 :1'


A system would typically comprise of three main parts :

1) The heat pump box.
2) The 'central heating pipe circuit' (LPHW or LTHW circuit).
3) The under ground pipe loop.

The Heat pump box :

The heat pump itself is a 'stand alone' box, primarily containing a refrigeration compressor and two refrigerant-to- water heat exchangers. Through the action of the refrigeration compressor, the first heat exchanger is chilled and absorbs heat from the water circulated through the underground pipe loop. The second heat exchanger becomes hot and gives heat to the water circulated through the central heating pipe loop.

In essence, the ground source heat pump takes the place of a conventional fuel boiler as the primary heat source.


The 'central heating pipe circuit' :

The 'central heating circuit' is identical to that for a conventional fuel boiler. Water is pumped around the central heating pipe circuit, passing through the hot heat exchanger within the heat pump box. Within a domestic house, the central heating circuit could comprise of radiators and a hot water cylinder etc in an identical way to a conventional fuel boiler system, the difference being that the ground heat pump replaces the fuel boiler in the circuit.

With a modern newly designed house, it would be normal to utilise an under floor heating tube circuit, instead of wall mounted radiators.

underground pipe loopThe under ground pipe loop :

A closed loop circuit of polyurethane pipe which would be buried in the ground adjacent to the building. Water, with an anti-freeze agent, is pumped around the pipe loop, passing through the chilled heat exchanger within the heat pump box.

There are two common types of ground pipe loop :

Horizontal slinky : Here the polyurethane pipe is coiled and laid horizontally along a long trench, but only around 1 to 2 metres below the surface.

Bore hole : Here a deep vertical hole is drilled into the ground and the polyurethane pipe loop is dropped down into the deep hole.