A Ground Source Heat Pump (GSHP) is another example of a renewable energy system you can have in your home. But how do they work? What do you need for a GSHP? What are the advantages and disadvantages? And do you really save money with them?

Let’s explore the technology and see if it’s the right fit for you…

How do they work?

GSHPs extract heat from the ground which is then utilised inside a house or building, where it can be used for space or water heating. As the temperature of the ground below the surface remains stable all year, this process works continuously, unaffected by weather conditions on the surface, making it slightly more efficient than air source. However, recent technological advancements in heat pumps have narrowed the gap between ground and air source, especially at lower flow temperatures.

GSHPs extract or deposit thermal energy through a series of pipe loops buried in the ground or in a body of water. This energy is typically absorbed at low temperatures into a fluid called brine which is contained inside the loops of pipe. These pipes are called ground loops or ground collectors. Ground loops can be installed either horizontally, at least 1 metre below the surface of the ground, or drilled down vertically (known as a borehole) 80m – 200m below the surface of the ground. The brine then passes through a compressor inside the GSHP, that raises it to a higher, more useable temperature (between 40-60°C), which can then be transferred to the water in the heating and hot water system via a heat exchanger. This process can also be reversed in the summer to deposit heat from the property back into the ground, providing passive cooling during the warmer months. By recharging the ground with heat in the summer, the efficiency of the heating season is therefore also improved.

Electricity is needed to power the compressor, meaning the GSHP is not completely carbon neutral but in the right conditions, GSHP can turn 1 kWh of electricity into 3 – 4 kWh of heat energy. Combining heat pumps with solar panels and battery storage can be a very effective way to reduce both energy costs and carbon emissions.

What do you need for a heat pump?

Ground source heat pumps require a large area of available ground if installing a horizontal array and careful consideration must be given to the disruption that would be caused by digging trenches or turning over large areas of land. If considering a vertical borehole installation, access for drilling equipment and space for drilling spoils must be assessed. A full ground survey should be undertaken to check if the ground is suitable.

The ground loop installation will require approximately 40m – 80m of pipe per kW load but requires careful calculation, considering ground type and water content. Soft, moist soil will be more effective for heat transfer. Hard, dry ground will require longer pipes, and therefore more ground, to absorb and extract the same amount of energy.

A typical GSHP unit is the size of a large fridge, so you can be installed in the house or in an outbuilding; however it is preferable to put the pump as close as possible to the collectors, to minimise heat loss.

What are the advantages and disadvantages of ground source heat pumps?

The benefits of GSHPs are:

• It could lower your fuel bills, especially if you replace more expensive fossil fuel heating, such as LPG or electric storage heaters.
• With regular servicing, minimal maintenance is required.
• GSHP are sometimes slightly more energy efficient than Air Source Heat Pumps (LINK to ASHP explained)
• If you live in England or Wales, you could access £7,500 from the Boiler Upgrade Scheme (BUS) | Ofgem to help fund your installation.
• Compatible with both underfloor heating, radiators, and fan coils.
• Dramatically reduced carbon emissions over fossil-fuelled boilers.

The drawbacks of GSHPs are:

• Space – A large amount of ground may be required.
• Initial cost – GSHPs cost roughly double the cost of an air source heat pump installation.
• The heat they deliver is 40-60°C compared to high temperature gas and oil systems which operate at 50-70°C.
• If retrofitting to an existing house, some radiators and pipework may need to be upgraded.

Are Ground Source Heat Pumps noisy?

This a common question for those considering installing GSHPs and the answer is that noise isn’t a problem. Although there are some components to a GSHP that make noise, they are less noisy than an old oil boiler. As an example, if you stand one metre away from where the pump is installed, the decibel level is around 41, similar to the same sound power level of people talking or normal background noise.

How much does it cost to install a Ground Source Heat Pump?

Typically, GSHP costs start from £15,000 to install (excluding groundworks), although prices vary considerably depending on the size of the system. This initial cost will be offset by the reduction in fuel bills. An investment in a GSHP system is an investment for the long term; the groundworks have a design life of 100 years and the GSHP itself has a life longer than any combustion boiler.

As a GSHP uses a small amount of electricity, if you have solar PV panels then the running costs will be even lower.

Do you really save money with a heat pump?

Savings depend on what system you use now, along with many other factors including your typical energy usage and insulation of your house. Taking into consideration a well-insulated four-bedroom detached home, over a year these are the savings you could make:

• £550 from an old (G-rated) gas boiler
• £2,000 from old electric storage heaters
• £1100 from an old (G-rated) LPG boiler
• £600 from an old (G-rated) oil boiler

(Reference: Energy Saving Trust)

Not only do you save money, but also on CO2. Per year you can save up to:

• 4,500kg on a (G-rated) gas boiler
• 5,200kg on an (G-rated) LPG boiler
• 3,600kg on an old electric storage heater system
• 6,900kg on a (G-rated) oil boiler

(Reference: Centre for Sustainable Energy)

Successful use of a GSHP depends on a variety of factors not least the efficiency of the building itself and what other source of fuel you have available. GSHP’s tend to be better suited to new-build homes, as they can be planned as part of the construction process. However, GSHP are available to anyone with enough land space for installation.