Listed Building Ground Source Heat Pump

Cambridge historic building energized by water

Keith Clarke and his family recently moved to River Farm, Haslingfield: a grade II listed building dating back to the 17th Century which was once owned by the pioneering Chivers family, the jam makers.

Ground Source Heat pump listed building

Old river farm

Ground source heat pump listed building

river farm now


The property covers a large farm house, a lake, various outbuildings and just over 4 acres of land. Mr Clarke wanted to change the 20 year old mains gas boiler which struggled to keep the house up to temperature and was expensive to run. Undertaking a 21st century renovation of the property is nothing unusual, however a key component of the process was the installation of a ground source heat pump (a Kensa 24kW Single Phase Twin Compressor) in his nearby lake which provided all the homes space heating and hot water.

Watch the video case study here

In the initial consultation Cernunnos recommended Kensa Heat Pumps as a preferred supplier of ground source heat pumps, because its models are manufactured in the UK and also because the Kensa 24kW Twin Compact, the largest single phase compressor on the market, was best placed to handle the property’s high heat load.

The challenges of working with a Grade II listed property

Keith was aware of ground source technology and knew it was an environmentally friendly choice eliminating reliance on fossil fuels. He approached experienced Cambridge-based renewables installer Cernunnos to talk about designing a ground source system that would meet the family’s heating and hot water needs.

The main challenge was to ensure that the heating system can work at lower temperatures and that
the energy efficiency of the property was considered and improved on. The less efficient the property, the greater the heat loss, which would result in a bigger and more expensive ground source heat pump and associated running costs to maintain temperature in the home.

Cernunnos undertook a detailed heat loss study at the start of the project which showed that the house had previously installed basic insulation measures to improve its heat loss; however the annex building where the heat pump is housed was poorly insulated. Cernunnos therefore installed extra insulation underneath a suspended timber floor using 100 mm rigid insulation between and 25mm below the rafters, as well as adding loft insulation.

The heat loss study also showed that many of the existing radiators on the second floor were already oversized and simply needed upgrading from single to double panels. Oversizing radiators ensures that they will work at a lower flow temperature, thus reducing the amount of work the heat pump is required to do to ‘uplift’ the renewable heat energy from the ground to the required temperature for the home.

Downstairs Cernunnos installed underfloor heating which provided both an even heat and minimal disruption to the original features of the property.

Peter McKeown, Director at Cernunnos said: “underfloor heating provided an ambient temperature delivered by the heat pump, which together with the new radiators ensure an efficient installation all round. We also recommended that the Clarke’s use state of the art Honeywell Evo-Home heating controls to allow them to control the temperature independently in every single room.”

As a listed building Cernunnos worked together with South Cambridgeshire District Council who were whole heartedly supportive to giving planning permission. Peter joked:” the listed buildings officer was even helping us with the digging!”

<H3>Harnessing heat energy from a natural water source</H3>
The lake on the grounds is fed by a natural spring. Cernunnos measured its flow rate, area and depth, and provided this information to Kensa who recommended that the Clarke’s use the heat energy in the lake for their heating and hot water.
The Cernunnos team sunk five specially created Kensa pond mats consisting of 300m of slinky pipe attached to weighted and corrosion resistant stainless steel frames to the bottom of lake. They connected the closed loop system up to the heat pump housed in an annex building via pipes running under the lawn up to the main house. This method removed the need for large amounts of drilling or digging, thereby reducing the cost and duration of the installation.

Keith commented: “When you see the property now it looks totally untouched you would never believe there are pipes in the garden and a heat pump in the lake!”

Chris Davis, Commercial Director at Kensa Heat Pumps said: “More and more people are realising that they can use water as a heat source for their ground source heat pump as it is an excellent conductor. In this case, the Clarke’s lake has a natural stream flowing into it replenishing the energy supply and creating a highly efficient water source system.

“The property had a high heat load on a single phase power supply, so Kensa’s 24kW Twin was perfectly placed to provide the required levels of heating and hot water. The measures that Cernunnos took to improve the heat loss of the building, taking into account its Grade II listed status, meant that the Clarke’s benefit from lower running costs too.”

Saving money through system efficiencies and Government grants

Mr Clarke said: “I knew that ground source was a great technology for extracting the natural heat that’s available from the environment to provide a completely green heating system. The good thing about the pipes being in the lake is that water has great conductivity meaning we are able to extract heat sustainably throughout the winter to keep the house perfectly warm.

“I know that there’s a big investment involved in getting a ground source heat pump, however we realised that we could get the whole thing paid for with the Renewable Heat Incentive, including the installation. Plus, we’ve ended up with a system where the yearly cost of electricity is less than we would have been paying for gas.”

Written by Leemya McKeown

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