Self Build property with slinky pipes - copyright Kensa Heat Pumps
Kensa Stephanie Gregory


Stephanie Gregory, Director of Marketing, explains how a ground source heat pump works, the advantages of the technology and the types of property they are best suited to in this interview for Build It magazine‘s Heating Special, due to be published in November 2019.



1. How do ground source heat pumps work?

A ground source heat pump extracts solar energy stored in the ground or water via submerged or buried pipework (ground arrays) and converts this to a higher temperature to meet 100% of a building’s heating and hot water needs, all year round. Heat naturally flows from warmer to cooler places, a ground source heat pump follows this basic principle by circulating a cold fluid around the ground arrays, which absorb and attract the ground’s low-grade heat energy. The ground source heat pump then compresses and condenses this heat energy and transfers it to the property’s heating and hot water system. Having surrendered the heat energy from the ground to the heat pump, the fluid from the ground arrays continues its circuit back to commence the cycle all over again.


How does a ground source heat pump work? Illustration

We all have heat pumps in our home already – standard refrigerators act like heat pumps in reverse by moving heat out of a fridge. Not to be confused with air source heat pumps, ground source heat pumps extract heat from the ground or water, as opposed to the air; the temperature in the ground remains a stable 8-10C all year round, making ground source heat pumps an extremely reliable and efficient heat source, especially at winter when the air temperature is colder than the ground temperature (and when you need heat most!).

Also not to be confused with geothermal heating; geothermal heat comes from the earth’s core. In the UK you have to go down 500m – 2500m before there is any appreciable input from the earth’s core. This form of heat tends to be used directly by very large-scale applications. Ground source heat pumps tend to go to 200m (if using borehole ground arrays – vertically drilled pipework), or ‘slinkies’, coiled pipework buried in trenches to a depth of 1m – 2m.

2. What are the main advantages of ground source technology (for homeowners specifically)?

By using freely available heat energy from the ground, the electrically powered ground source heat pump delivers three times more energy than it consumes, significantly reducing running costs – for every 1kWh of energy your heat pump uses to power itself, you will get typically 3kWh of heat. Better still, to offset the additional cost of installing a ground source heat pump over a fossil fuelled system, the Government’s Renewable Heat Incentive pays a quarterly income for ground source heat pump installations for 7 years (or 20 years if you have a commercial property or two or more properties sharing the same ground array).

District ground source systemThe bigger picture? Aside from the clear sustainability benefits of ground source heat pumps, they emit no point of use carbon emissions or air pollution, helping to significantly improve air quality. With gas being ruled out for new builds from 2025, Kensa sees ground source heat pumps as the means to rival and replace the gas network; by installing individual ground source heat pumps in each home, each heat pump can be connected to a communal ‘shared ground loop array‘; Kensa’s innovative district heating system, which allows for developments of two or more properties to benefit from having a ground source heat pump independently owned and operated in each dwelling, all connected to a communal infrastructure much like the current gas framework; yet much more safe, ultra low-carbon, and sustainable. Kensa Contracting is currently utilising this system in many new build homes across the country as well as retrofit scenarios, from luxury apartments on the beach in Cornwall, to an eight tower block scheme in the centre of London!

3. What type of property would be a good fit for ground source heat pumps?

A misconception is that ground source heat pumps are not suitable for properties with poor levels of fabric efficiency, i.e. insulation. In fact, all homes should be well insulated for all heating types: for heat pumps it is not essential, but equally desirable. Indeed, Kensa heat pumps are installed in a diverse range of properties, from Grade II listed manors, to flats and tower blocks, to eco homes, and even canal barges.


Tuckers Close ground source heat pump case study: external shot of the closeNew build homes, due to their higher levels of fabric efficiency, benefit from improved heat pump efficiencies, and therefore a smaller sized ground source heat pump compared to their retrofit equivalent.

Historically most ground source heat pump customers were in rural off gas locations where alternative forms of heat are not easily accessible. However, ground source heat pumps with shared ground loop arrays are making the roll out of the technology viable at scale, indeed they are also taking on the gas infrastructure, following recommendations by the Committee for Climate Change (CCC) that new build homes as of 2025 should be connected to a heat pump infrastructure, potentially ruling out gas in these scenarios in just six years.

Far from being a ‘niche technology for the wealthy few’, Kensa is encouraging and enabling the mass adoption of ground source heat pumps to dramatically reduce heating bills and improve living conditions for those in society who will benefit the most, without them having to pay a single penny. This is evidenced in the thousands of retrofit heating installations Kensa Contracting have delivered in both rural and urban social housing across the UK.


4. Do you have any advice for homeowners considering ground source installations? 

Costs for a ground source heat pump installation are unique to each and every project, but for a ballpark figure a single Kensa Evo ground source heat pump fed by a slinky ground array for a typical new build property could cost £14,000, and earn you £24,000 income from the Domestic Renewable Heat Incentive (RHI).
We have outlined typical costs on our website here:
The flyer is particularly useful for comparing costs to an LPG boiler.

When you combine heat pumps with smart meters and smart controls, remote grid balancing and time of use tariffs, heat pumps can have a positive effect on the grid by turning on when there is overgeneration (instead of turning wind turbines off like we do now), and by turning off when the grid is under strain. This is particularly true for ground source – because the source temperature is more stable, they can be run overnight without loss of efficiency. Our grid generally has most excess capacity overnight – some of the variable tariffs actually go negative on some nights so people can get paid for running the heating!

The smart metering has given rise to the ability to charge consumers different prices for their electricity at different times of day which reflects the reality of the wholesale electricity market. Smart thermostats allow property needs data (temperature, humidity, comfort levels) to be exported to remote servers where the heating controls can then be optimised and new schedules sent back to the thermostat. By linking the heating control server with the electricity price server, the revised heating schedule can move heat pump operation from high priced to low priced times of day. Modelling has shown savings of 25-40% are possible. Better still, lower priced times of day typically coincide with lower carbon grid electricity – this is because wind, nuclear and solar provide a lot of the baseline while higher carbon sources of electricity are deployed when the grid needs boosting.

Installation of a Kensa ground source heat pump is a relatively simple affair, as Kensa heat pump systems are specifically designed to be installed by contractors without the need for specialist training. Any competent builder and plumber should be capable of installing them. Kensa’s ground source heat pumps are designed to be similar to install to a standard boiler. Much like the product, it is critical that the installer is MCS accredited (Microgeneration Certification Scheme) to ensure the system is commissioned to receive the Renewable Heat Incentive – Kensa offers an MCS Umbrella scheme for those who are not MCS accredited.

The ground works can be undertaken simply by any groundworks contractor. Borehole installations require specialist surveys and drilling rigs, whereas slinky trenches are capable of being installed by any savvy self builder.

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