03 June 2025
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Neil Lawson, Managing Director at GeoEnergy Design (GED), discusses a project where a ground source system is at the heart of an innovative energy solution — providing heat for an indoor pool and supplying all the electricity for the house, all for less than £6 per day during winter.
When news broke in 2023 that Rishi Sunak had installed an indoor heated pool in his North Yorkshire mansion, I quietly hoped it was heated by a heat pump. When I dug further, headlines were abundant like ‘Rishi Sunak’s new private heated swimming pool uses so much energy that the local electricity network had to be upgraded to meet its power demands, the Guardian has been told.
Articles state, ‘Construction work on Sunak’s private 12-metre (40ft) swimming pool has finished just as many councilrun baths, including in his local area, are being forced to reduce their opening hours owing to increased energy costs. This week, the House of Commons Culture select committee called on the government to offer extra help to swimming pools in the forthcoming budget, suggesting 350 pools had closed or cut their hours as a result of energy costs.
Articles like this, regularly featured in the Guardian make me want to scream! Heat Pumps are part of the solution, not the problem if considered and designed appropriately!
The project: Build an indoor pool that cost very little to run
In March 2022, a long-term business associate contacted GED, wanting to build an indoor pool that cost very little to run. He had already installed a condensed 48kW peak solar farm in the space of a tennis court with 100kVA 200kWh battery to power his house, and now he was ready for a GSHP for his new pool project, and he hoped that GED could design the solution.
Nearly 3 years later, his very dream is a reality. In our dreary wet winter, the running costs are averaging £6/day, but as the sun made an appearance in early April, running costs dropped to zero.
Done correctly, Rishi Sunak and indeed the government could have saved money on costly grid upgrades, instead investing it into onsite generation and storage. If we manage our demand, then the grid could shrink, not collapse as certain sectors of the press would have us believe.
The go-to technology for a pool builder is the old faithful Air Source Heat Pump (ASHP), cheap and cheerful, harvesting low-grade heat from the atmospheric air, and compressing it to generate useful heat to heat a pool. They need very little design capability and when sized correctly are a f it-and-forget. But they are a compromise. The challenge with an indoor swimming pool is that they are intrinsically energy-hungry, even requiring heat in a UK summer. The pool hall air is kept at 2°C above the water temperature, which is typically 28 to 31°C to reduce evaporation. This continual draw on the harvesting of low-grade ambient heat through boreholes or a horizontal collector result in a system hugely oversized when a 50-year sustainable energy model is created. Putting waste heat back into the ground during the summer months makes a significant difference in reducing the size of a collector. The lifespan of a collector is 120 years, hence the need to model over 50 years. The conversation started around ‘free cooling’. Cooling is a by-product of heating with a heat pump, so if you can utilise both sides of the equation, suddenly, the COP (Coefficient of Performance) starts to add up. A COP of 5 for heating and 3.5 for cooling means that 1kW of electricity can generate 8.5kW of useful coolth and heat, also quoted as 850% efficient. In this instance, there was no local need for cooling, although we are seeing increasing demand as the UK experiences warmer summers.
Another way to recharge the boreholes is using solar thermal. The Mansard roof design on the pool building created a hidden well where 20kW of solar thermal could be secreted. Combining solar photovoltaic with solar thermal has a similar double benefit to simultaneous heating and cooling with a GSHP where the harvesting of heat from the PV panels, thereby reducing their temperature increases the efficiency of the PV.
Traditionally solar thermal is used to heat domestic hot water to 65°C, but here we have the perfect scenario, whereby once the DHW is satisfied, the solar thermal switches to heating the pool hall, then pool water and finally recharging the boreholes. In this way, you can harvest 5x more solar thermal from the sun than a simple DHW system, even in the depths of winter or cloudy days, when the panel temperature only needs to be 5°C more than the ground temperature to transfer heat. The owner knew of Naked Energy, so an introduction was made, and a deal was struck.
How do we marry all these technologies together and really make them work – experienced designers! Origin Pools and Heatstar were very open to being challenged on their traditional build specification, to create something truly innovative and efficient. Naked Energy who produce PVT tubes, a combination of solar thermal and photovoltaic panels shared all their performance data down to the minutiae detail, enabling a solution that could be worked out from the ground up. The client said of the project: “Firstly the installation is working fantastically, and the installation is really impressive in terms of performance. Everything from the Naked Energy tubes to the ground source heat pumps etc is linking together well and with the battery, we are covering all the electricity at £6/day including the house in winter”
The final specification:
GSHP – CTC 40kW, 5no. 115m boreholes Installer: Baystar
PVT – Naked Energy, 5kWe, 20kWth
PV – 48kW
Storage – 200kWh
Pool: 14m L, 4.5m W, 1.3m D
Spa; dia. 2.5m
Pool is insulated underneath as well as the sides.
Pool cover: automated
Pool air handling: Heatstar XF EC4000 Super
Pool water heat exchanger is external with 35C primary LTHW setpoint.
DHW, UFH from GSHP
Pool Builder: Origin Pools
