Renewable heat
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Heat pump systems can easily replace fossil fuel boilers, such as oil or electric fired boilers as they are of similar size. Hot water can then either be distributed through a radiator system to provide space heating or to a hot water cylinder to provide hot water.

As is typical of all energy efficient products, heat pumps are characterised by an initial cost which is directly related to the heat output of the system. It is therefore important to size the heat pump according to the heat loss of the dwelling.

For urban settlements, it is important to ensure that the heat loss of the average size building of say 75m2 does not exceed 5.0 kW(h) at -10°C if the geothermal heat present in the underlying aquifer is to be shared equitably between all inhabitants. This upper limit will require additional insulation to be added to the older housing stock in the UK in order to reduce its heat loss.

Since the hot water temperature from a heat pump system will be lower than that of fossil fuel boilers, it is important to improve the insulation level of the dwelling in order to retain the same size of radiators.

In addition it will also be necessary to maintain the thermal efficiency of any radiator system by adding a corrosion inhibitor in order descale the radiators by taking corrosion products plated on the inside of the radiators back into solution. Then to check at the annual service that the water quality is maintained at its neutral level (pH 7.00) by adding additional inhibitor if necessary to ensure limiting corrosion.

One option for locating a GSHP heat pump is in a cupboard with the hot water cylinder mounted above (as illustrated).

Figure 6kW GSHP manufactured by Kensa below with a 150l hot water cylinder above


Reducing the conversion cost

The biggest cost of ground source heat pump systems is the cost of drilling the borehole and so it is always economic to drill an array of boreholes while the drilling machine is on site. The geothermally heated water from these boreholes can then be circulated via a flow and return pipe (ground loop) to a cluster of homes in each of which is located an individual heat pump.

The optimum time to undertake the conversion to low carbon heating systems is when the existing boiler (or electric storage heaters) needs replacing provided that it is possible to access a ground loop in which geothermally heated water is circulated.

Such district energy networks are likely to become more common in future in order to be able to install low carbon forms of heating using ground source heat pumps.

KITH # Activity Age range
7.4 Geothermal heating using heat pumps
  Geography, Science
 12 – 18  



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