Ground Source Heat Pumps

How does a GSHP work?

A Ground Source Heat Pump transfers heat from the ground into buildings.

Radiation from the sun heats the earth. The earth then stores the heat and maintains, just two metres or so down, a temperature of around 10°C even throughout the winter. A ground source heat pump uses a ground heat exchange loop to tap into this constantly replenished heat store to heat buildings and provide hot water.

How efficient are Ground Source Heat Pumps?

For every unit of electricity used by the heat pump, three to four units of heat are captured and transferred. In effect this means a well installed Ground Source Heat Pump can be 450% efficient in terms of its use of electricity. At this efficiency level there will be 70% lower carbon dioxide emissions than for a gas boiler heating system. If the electricity is provided by renewable energy such as Solar PV, then carbon emissions can be reduced to Net Zero.

What do they look like?

A Ground Source Heat Pump system comprises three basic elements – a ground heat exchange loop, the heat pump itself which concentrates available heat from the ground, and a building heat distribution system, such as UFH or Radiators.

The ground loop is a pipe buried underground in a horizontal trench or if required via a vertical borehole.

Horizontal trenches are typically dug 1.2 metres below ground level and, although needing more land area than a borehole, they are usually much cheaper for smaller systems. Boreholes are drilled to a depth of 80 to 120 metres and may benefit from higher ground temperatures than horizontal trenches.

The ground area required for trenches will vary with the ground condition (its thermal conductivity), the property, its location and the heat load required. As a general guide, for a newly built 5 -bedroomed house of around 270m2 with a heat loss of around 12kW, four trenches of 75 metres in length would typically be required, that requires a circ 550m2 of space for installation.

A non toxic, heat transfer fluid such as Kilfrost GEO / water mixture is circulated through the pipe where it absorbs heat from the ground. A heat exchanger then extracts the absorbed heat and transfers it to the heat pump. The third basic element of a ground source heat pump, the heat distribution system, can be either low temperature radiators or, preferably, underfloor heating. If the heat pump is asked to produce higher temperatures, for use with conventional radiator circuits, then its efficiency is likely reduced.

Once a ground source heat pump is installed, there are no external fans and no external equipment is visible. The system is quiet in operation, issues no emissions, is very safe and requires very little maintenance.

Installation Costs

The installation costs will depend on the site and the amount of heat output required. A site survey is necessary to determine which type of collector (horizontal trenches, vertical borehole) is most appropriate. As an indicative guide, the installed cost of a horizontal GSHP system is likely to be in the range £1,550 – £1,750 per kW of capacity, with that for a vertical borehole closed-loop system in the range £1,750 – £3,000 per kW. However, the cost will be specific to the type of property and technical approach required. The Renewable Heat Incentive is a major financial encouragement to install ground source heat pumps: Ofgem will pay upto 20.46 pence per kWhr of eligible heat generated every year for seven years. (See Ofgem Website for latest incentive rates)

GSHPs can be installed anywhere in the UK, using a borehole or trenches or, less commonly, by extracting heat from a pond or lake.

Ground source heat pumps have been widely used in North America, Sweden, Germany and Switzerland for many years. Typically they cost more to install than conventional heating systems. However, they have very low maintenance costs and can be expected to provide safe, reliable and emission-free heating.

Running Costs

The running costs of a well designed ground source heat pump system are lower than for any other space heating system, whether fossil fuel based or renewable. Savings in running costs of 30% to 70% can be achieved depending on the type and price of fuel being displaced.

The only energy used by a ground source heat pump that you pay for is electricity to power the compressor and the circulation pumps which transfer heat energy from the ground into the building. A well designed ground source heat pump installation will deliver three or four times as much thermal energy (heat) as is used in electrical energy to drive the system.

Ground source heat pumps work best with heating systems which are optimised to run at a lower water delivery temperatures, as such, they make an ideal partner for underfloor heating, “oversized” radiators or smaller fan assisted convection radiators.

The Advantages of Ground Source Heat Pumps

Ground Source Heat Pumps offer much lower running and operational costs, they are much cheaper to run than direct electric heating, oil boilers, burning coal, or LPG. This is before taking into account the receipt of RHI which can often make a significant contribution toward the cost of installation.

  • Heat pumps save space. There are no fuel storage requirements.
  • No need to managed fuel deliveries. No risk of fuel being stolen.
  • Heat pumps are safe. There is no combustion involved and no emission of potentially dangerous gases. No flues are required.
  • GSHPs require less maintenance than combustion based heating systems.
  • Heat pumps save carbon emissions. Unlike burning oil, gas, LPG or biomass, a heat pump produces no carbon emissions on site (and no carbon emissions at all, if a renewable source of electricity is used to power them).

A well designed ground source heat pump system is likely to increase the sale value of your business or property.

Performance of Ground Source Heat Pumps

The performance of a heat pump is measured under standard conditions as the “coefficient of performance”: this measures the heat output in kilowatts in relation to the electrical input in kilowatts. However, the CoP of a heat pump is greatly influenced by the output temperature delivered to the heat distribution system in the building and the input temperature from the heat source.

In cold conditions a ground source heat pump with access to a temperature of 10°C from the ground will deliver a significantly higher CoP than an air source heat pump with access to -5°C from ambient air. The design, installation quality and controls of a ground source heat pump installation are critical to achieving good performance.

Heat Pump Systems

There are three types of heat pumps: air-to-air, water source, and geothermal. They collect heat from the air, water, or ground outside your home and concentrate it for use inside.

Air Source Heat Pump

Ground Source Heat Pump

CO2 High Tempertaure Heat Pump

Green Home Grant

You can now get a government grant up to £5,000 or £10,000 to help cover the cost of energy efficient improvements to your home. You can apply for a voucher from the end of September 2020.

The government will provide a voucher towards the cost of installing energy efficient and low-carbon heating improvements to homes in England. The voucher will cover up to two-thirds of the cost for homeowners and landlords, and up to 100% of the cost for low-income households.

The Boiler Upgrade Scheme will launch in April 2022 to help homeowners and small business owners in England and Wales afford the upfront costs of heat pumps and biomass boilers.

Read More on Eligibility….