Many people imagine that ground source energy originates from deep within the earth. This is type of energy is in fact geothermal energy, and typically has nothing to do with ground source heating systems.

Ground source energy originates from the Sun. The Sun warms up the ground surface during the day, like a huge solar panel. At night, most of the heat is radiated back into the air. However, some of the heat is transferred below the ground surface, where it can be converted into useable heat by ground source heating systems. Consequently, a potential user does not have to live close to an area of ‘hot rock’ in order to utilise ground source heating!

The temperature of the ground in the UK, 1-2m under the surface is typically 10-12 degrees Celsius. A comfortable temperature for homes and offices is typically around 22 degrees Celsius. Clearly there is a discrepancy between the two. Ground source heat pump systems are able to convert large quantities of low grade heat into smaller quantities of high grade heat, sufficient to heat buildings and pre-heat domestic hot water.

This is how it works:

The heat pump essentially consists of three pipe circuits and two heat exchangers.

The ‘Collector’ circuit (3) conveys a low temperature fluid (often called brine) through trenches or boreholes where it is warmed by the ground (see diagram below). The acquired heat is transferred to the ‘compressor/condenser’ circuit inside the heat pump via a heat exchanger.

The ‘compressor/condenser’ circuit forms the heart of the heat pump. Refrigerant warmed by the first heat exchanger passes through a compressor (4). Compression of the fluid generates temperatures high enough to heat tanks for under floor heating and domestic hot water. This heat is transferred to the ‘heating’ circuit (1) via the second heat exchanger.

The ‘heating’ circuit picks up heat from the second heat exchanger and transfers water, typically at around 40 degrees Celsius to the application, usually buffer tanks to be used for underfloor heating of domestic hot water. The return water from the application completes the circuit.

After passing through the second heat exchanger, the fluid in the ‘compressor/condenser’, now much cooler (2), passes through the condenser which brings about further cooling of the fluid. The cold fluid then returns to the first heat exchanger and circulation is repeated.