What are heat pumps?
A GSHP system consists of a ground heat exchanger, a water-to-water or water-to-air heat pump, and a heat distribution system. A heat pump can take low temperature heat and upgrade it to a higher, more useful temperature.
What types are available?
Horizontal
There are 2 types of horizontal systems available; single and multiple pipes. The pipes lay in a horizontally dug trench.
SLINKY system - the pipe is laid as a series of overlapping coils.
A direct-expansion (DX) system uses refrigerant in the ground-heat exchanger, instead of an antifreeze solution.
Vertical
The pipes lay in a vertically dug hole.
Installation
First the correct depth has to be reached. Then a flexible dual-flow pipe (DFP) is installed through the casing to the base of the casing. The casing is pulled back to ground level, leaving the DFP in direct contact with the soil over the depth of installation. The pipe is then connected to a network of DFPs laid within near surface trenched, which are then backfilled and the surface is leveled.
Duration
The heat exchanger is buried either horizontally in a shallow trench (at a depth of about 1m) or vertically in a borehole.
Costs
Single or multiple pipe horizontal systems generally will be slightly more expensive than Slinky systems because the cost of additional trenching will outweigh the reduction in the material cost for the piping. DX systems are also likely to be cheaper than the equivalent output indirect system as they require less ground coil. The actual costs for the ground heat exchanger will depend not only on the installed capacity of the heat pump but also the energy demands of the building and the ground conditions.
System Type |
Ground coil costs |
Heat pump costs |
Total system costs |
Horizontal |
250 – 350 |
350 – 650 |
600 – 1000 |
Vertical |
450 – 600 |
350 – 650 |
800 – 1250 |
The running costs for a GSHP system are largely dependent on the associated fuel costs. The fuel used for the heat pump is electricity and usual tariff rates normally apply although some suppliers offer a special heat pump tariff. Maximum advantage should be taken of any preferential tariffs (off-peak, etc) in order to keep annual costs as low as possible.
Maintenance costs for GSHPs are minimal. The average payback is 5 to 7 years.
Grants
The grants available for heat pumps are for a maximum of £1,200 or 30% of the total installed costs.
The amount that the grants cover are for costs made before the VAT is added.
After a grant is granted the installation has to be completed within 6 months.
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