Self-sufficiency in heat and power for detached new-build
When David and Trish Elvidge set out to build their forever home on land they already owned in East Riding, Yorkshire, they knew they wanted a holistic heat and power solution that would seamlessly integrate different technologies to achieve their specific environmental and lifestyle goals. Comfort, efficiency and self-sufficiency were key, as well as keeping costs and emissions as low as possible. The couple also wanted the air in their new three-bedroom house to be free of dust and pollen, following David’s experience ventilating work spaces.
At the heart of the new system is a Viessmann Vitocal 222-G 8 kW ground source heat pump with integrated 220-litre hot-water cylinder. Ground source heat pumps offer a year-round, eco-friendly, renewable source of energy for heating and hot water by using geothermal collectors to gather natural heat from the ground. In this case, this is done via two 100 m boreholes, due to David and Trish’s garden space measuring at 25 x 25 metres.
As well as being unusually compact, quiet, and easy to operate, the Vitocal has exceptionally low running costs thanks to its optimised seasonal efficiency and the fact its hot water cylinder sits on top of the pump itself. It has a coefficient of performance of 4.6 and an energy efficiency rating of A+++ / A++.
“For the design conditions at this property, the Vitocal is the most efficient ground source heat pump on the market,” explained Paul Leedham of Matrix Energy Systems. “We further enhanced its performance with the addition of extended collectors from MuoviTech to increase the return temperature from the ground. Each degree Celsius above 0 gives around 3% improvement in output power, providing around 24% extra output power, boosting the 8 kW unit to a 9.92 kW output.”
Additional hot water storage was incorporated via the inclusion of a Viessmann Vitocell 100-E heating water buffer cylinder. This is used to feed the underfloor-heating system that runs throughout the ground floor of the building with a maximum flow temperature of 35oC, as well as the upper floor’s over-sized radiators that have a maximum flow temperature of 45oC. Separate Viessmann weather-compensated controls for each zone ensure just the right amount of heat is provided, thereby eliminating waste.
A Blauberg smart-app-controlled mechanical ventilation and heat recovery (MVHR) system was fitted on the radial pipework. Running on low-power DC fans, it has a summer bypass for cooling and manifolds to reduce noise and increase efficiency. It also contains pollen and dust filters that remove particles down to 0.3 microns in size from the ambient air.
The MVHR system recovers over 80% of the ventilation heat in the property, drastically reducing demand on the heat pump and therefore energy consumption. There is an option to provide additional cooling in future thanks to the installation of specially insulated ducting to eliminate condensation. This would also further increase the efficiency of the ground source heat pump by adding recharge energy to the boreholes.
Everything is located in one place, with David, Trish and the team from Matrix doing all they could to site equipment in unused space. Space under the stairs on the garage’s ground floor, was used for the heat pump and water storage, while a loft area in the garage’s second floor which houses the solar panel inverter, battery storage and MVHR equipment.
Just as they’d hoped
Thanks to all these efficiencies, the power used to operate the heat pump is fully covered by 16 split-cell 325 W solar PV panels on the building’s roof. The panels are controlled by an app, with the 5.2 kW of energy they generate stored in an 8.2kWh battery for later use. Energy not needed by the Vitocal heat pump is fully utilised by the household for things like immersion heating and electric vehicle charging, thanks to an export-limiting technology which caps feedback to the grid at 3.68 kW.
“The whole house is lovely and warm, and we always have as much hot water and electricity as we need,” said David. “Even better is the fact that it’s not costing us anything to run! It’s just what we hoped for.”
The whole system is simple for David and Trish to control and operate using smart thermostats linked via two apps - one to control the solar and battery system and the other for the MVHR.
Drilling for the ground source heat pump bore holes took place in 2019 but the project was then largely delayed until mid-2021 due to COVID restrictions and supply chain issues. The project was fully completed and operational by early 2022. It was Highly Commended at the 2022 Energy Savings Award.