Ground source heat pumps present consumers with an ideal alternative to conventional gas or oil-fired boilers but are they more environmentally friendly and cheaper to run?
With conflicting advice circulating the media, some may find it hard to decipher fact from fiction, which is exactly why Nu-Heat wants to answer some of the questions most frequently asked about ground source heat pumps.  

How does a ground source heat pump work?
Ground source heat pumps (GSHP) work by using heat stored in the ground. They take advantage of the fact that the top 15m of the Earth’s crust maintains an average year-round temperature of approximately 12˚C.
Installation of ground collectors takes two forms, either by a series of horizontal trenches one metre below the surface or vertical boreholes. The pipe is usually a closed circuit and is filled with a mix of water and anti-freeze that absorbs heat from the ground. This is then concentrated by the heat pump and transferred to the building – this is then used in a low temperature heating system such as underfloor heating and to heat domestic water.  

What groundworks are needed?
Nu-Heat uses only horizontal trenched collectors or boreholes, both of which are spaced so as not to extract too much energy from a given volume of ground. If too much energy is extracted, the ground can freeze, reducing its ability to transmit heat to the collector. An area approximately equal to 2.5 times the floor area to be heated is needed to accommodate sufficient ground loops.  

Are GSHPs really environmentally friendly?
Yes. The best way to explain this is to look at the energy ‘in’ versus the energy ‘out’, taking into account the electricity used to power the heat pump’s compressor.

Government figures, as detailed in the Standard Assessment Procedure (SAP), state that for every kilowatt hour of electricity used, 0.42kg of carbon is produced, with gas generating 0.19kg of carbon for the same unit of energy.


Compare this with a heat pump achieving a Coefficient of Performance (CoP) of 4.0*, which is realistically achievable with a heat pump supplied by Nu-Heat, and 0.42kg becomes 0.10kg of carbon – considerably less than produced by gas or direct electricity (see equation below).

* This is the ratio of units of heat output for each unit of electricity used to drive the compressor and pump for the ground loop. A CoP of 4 means that for every kilowatt of electricity put in, you get 4 kilowatts of energy out in the form of warm water.

Put simply, in a well-insulated property Nu-Heat’s ground source heat pump can provide 3 to 4 kilowatts of free energy for every 1 kilowatt of electricity used to power it.  

It is also worth considering that a gas boiler is only ever 90% efficient, increasing the figure of 0.19kg to 0.21kg of carbon created (because the original figure is divided by 90%).

So, when comparing the energy use of a heat pump with that of gas, end-users will be reducing their carbon emission by 50%.

The GSHP Association states:

“Most electricity suppliers are now offering ‘clean green’ electricity from a renewable energy source and, if you use this to power your heat pump, your property will be totally heated from renewable energy with zero carbon emissions.” (Source: www.gshp.org.uk/faqs.htm <http://www.gshp.org.uk/faqs.htm> ). 

How do running costs compare with conventional alternatives?
Heat pump systems powered by standard tariff electricity can still produce 40% lower carbon emissions than gas fired, and 55% less than oil fired installations. This is due to the ‘free energy’ the heat pump harvests from the environment – and in many new build applications, heat pumps often generate the lowest running costs of any heating system.

Take a figure of 66 pence per litre of oil – this equates to 6.1 pence per kWh. Compare this to electricity at 6 pence per kWh, based on a mixture of peak-rate and off peak supply and electricity is expensive; but factor in a CoP of 4, and the cost of electricity effectively drops to approximately 1.5 pence per useful kWh. This is approximately 60% less than the oil figure, and half that of gas – and it is likely that the difference will increase further as fossil fuel reserves become depleted and greater amounts of electricity are generated by renewable means.  

What ongoing maintenance does a heat pump require?
A GSHP system is cheaper to maintain than a traditional boiler, as the unit does not require an annual service. 

What measures can be taken to make sure the heat pump system works efficiently?
Heat pumps are at their most efficient when the water produced is between 35˚C and 45˚C, far lower than would be practical for a conventional radiator system typically needing water at 65˚C or higher, but ideal for warm water underfloor heating.  

What if I already have a radiator system?
Heat pumps are capable of producing water of a higher temperature but the CoP will suffer, falling to between 3 and 4 when delivering water at 50˚C, still impressive, but falling short of its potential. Most reputable heat pump suppliers will recommend underfloor heating, however, when working with radiators, homeowners should be made aware of the potentially lower efficiency.  

How is the room temperature controlled?
All of Nu-Heat’s ground source heat pump models have an integral weather compensation function –this is where the heat pump monitors the outside temperature to determine what flow temperature is required to keep the house at a comfortable temperature.  
By calculating the difference between the required flow temperature and the actual flow temperature the heat pump can decide when to start and stop its compressor, ensuring long running times and maximising efficiency, whilst providing a balanced temperature throughout the property and avoiding the peaks and troughs associated with high temperature radiator systems. For example, on a warmer day the house will require a lower flow temperature to maintain a comfortable temperature than on a cold day.

Are there any other measures I can take to make the system more efficient?
Insulation levels will have a direct impact on the overall effectiveness of the underfloor heating and heat pump. Recent changes to Part L of the Building Regulations have focussed attention on the importance of insulation levels within domestic dwellings and the special care and attention required when underfloor heating is specified.

With underfloor heating, warmth passes into the room from the floor and it is therefore important to prevent downward heat losses into the ground or the floor below. In a new building that meets the regulations, there will always be an adequate level of floor insulation, but if a building is being refurbished and no extra insulation is provided then underfloor heating suppliers will recommend the required amount of insulation. In all cases, Nu-Heat recommends that the property’s insulation is increased to the level of Part L.