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Financial Considerations

To install a Ground Source Heat Pump system with boreholes requires a significant financial commitment. The obvious questions are therefore
  1. How much will it cost?

  2. What are the quantifiable advantages/benefits?

  3. Are there material incentives to encourage installations?

COST

This question can elicit an uncharacteristic coyness in some GSHP salesmen, who will try to keep this information to themselves until a very late stage in your negotiations. Or, in the worst case, try to mislead you by understating the borehole depths required in order to make the project look cheaper and their sale easier.If you have been given the required GSHP capacity in KW and the corresponding estimate of borehole depths required, check the calculation used.There are several obvious factors that influence the total cost. The size and capacity of the heat pump required is the most important.A small 2-3 bedroomed house may require a heat pump capacity of 6 -10KW and around 100-200m of boreholes, a larger residence with 4-8 bedrooms could need a 30-40KW pump and 500-900m of boreholes.*Other factors also play a significant role, the age of the house, quality of wall and roof insulation, suitability of distribution system, e.g. is there underfloor heating?Also, is the GSHP just required for heating, or also for hot water or even swimming pool heating?Having said all of that and emphasizing that each case will be different, you must expect to pay typically, for the size ranges above, somewhere between £1400 and £2000 per installed KW of GSHP capacity (excluding VAT @ 5%). This cost does not include any other equipment for distribution, e.g. underfloor heating, etc.

The cost per KW will be towards the high figure for smaller installations as the one off, transport and set up costs for the installer carry more weight.

As with many other things in life, the more installed KW capacity you buy, the cheaper the unit price becomes.

In terms of cost per square metre of heated area (assuming underfloor heating)

Both of the above graphics should be used only to arrive at a rough dimension for the project. Many factors can influence the cost upwards or downwards.

The total cost of your project is likely to be composed as below

(As an aside, this also shows that the drilling of the boreholes is very likely the single largest cost component in your project. Saving money by hiring the "cheapest" contractor can mean that costs will be saved, corners cut, where you will not see them. Faults in any part of your system above ground are relatively easy to correct, up to and including total replacement of the heat pump. Defects in the boreholes, leaks/kinks, drilled shallow, substandard grout, etc. will significantly detract from the overall performance of the system (and your hoped for savings!) and, as a rule, cannot be repaired.

* These figures can vary, mainly driven by two factors, 1) the efficiency of the heat pump, and 2) the thermal characteristics of the ground.

SAVINGS / BENEFITS / ADVANTAGES

The whole circle below represents the total amount of heating and hot water used in the building. The blue sector is the measure of your Carbon Footprint due to heating. This blue field indicates energy consumed by the heat pump, the red indicates additional energy which could be used during peak loads and the green indicates free energy. You can save this much energy                                            

GSHP manufacturers are keen to talk about COP, (Coefficient Of Performance). COP is the ratio between the energy, ie. electricity, put into the heat pump in order to make the electric motor driving the heat pump work, and the amount of heat extracted from the ground and pumped into your heating system as shown below.

                               

Typically, modern heat pumps have COP ratios of between 3 (as above) and 5, i.e. for every Kilowatt of electrical energy put into the system, 3 to 5 Kilowatts of heat energy are put into your heating network.

Hence the energy saving claims for heat pumps in general.

Warning

The calculation of COP ratios is considerably influenced by the choice of temperatures for the heat conducting medium entering and leaving the heat pump.

Manufacturers are naturally adept at choosing entry/exit temperatures to give the highest COP for their product. 

The general rule is, the smaller the difference between collector and output temperature the higher will be the COP, conversely the greater the difference, the lower the COP

Should you wish to make choices based on COP figures, make sure that you are comparing like for like, i.e the comparison is for the same temperature range.

 

SUMMARY OF GSHP ADVANTAGES

Efficiency - for every unit of electricity the ground source pump uses, it generates between 3 and 5 units of heat energy.

Low operating costs - a geothermal system can cut heating costs by up to 60% per year in some cases.

Environmentally friendly - a ground source heat pump can reduce your CO2 output by up to 2 tonnes a year. It can also be made carbon neutral if you buy green electricity, or generate your own.

Comfort - you are guaranteed a constant supply of reliable heat all year round. It can also be used in reverse during hot weather to cool buildings.

Safety - a ground source heat pump is very safe to have in your house. It does not require any combustible components. It is entirely electrically operated so there is no risk of carbon monoxide poisoning, no flame or bad smells.

Flexibility - geothermal energy has many applications from under floor heating and cooling, to heating a swimming pool and also for domestic hot water.

Quiet - a ground source heat pump is very quiet and discrete.

Consistency - as the temperature of the ground is the same almost all year round, you will always be guaranteed a constant flow of hot water.

Lifespan - a ground source heat pump's life span of about 30 years is about twice as long as a conventional boiler.

Carbon Footprint Reduction - Your house will have a lower carbon Footprint because you have extracted energy from the ground rather than from consumable fossil fuel