New trial supports hybrid approach to renewable heating

18 July 2024

As a nation, we are committed to reducing our greenhouse gas emissions to net zero by 2050. But the latest progress report[i] to parliament from the Climate Change Committee (CCC) raised concerns that the UK Government’s pace of delivery is proving too slow to meet future critical targets[ii]. This new trial supports hybrid approach to renewable heating, helping homeowners take a step in the right direction.

Buildings remain the UK’s second highest-emitting sector, accounting for 18% of total emissions[iii]. Innovative heating solutions are urgently required to meet the evolving energy needs of our country. One such solution is hybrid heating systems, a halfway house towards renewable domestic heating which, regrettably, have thus far been overshadowed by solar PV and standard air source heat pumps.

Now, a recent hybrid heat pump trial in Northern Ireland by heating engineer firm Refresh NI – in partnership with heating manufacturer Alpha – has shed new light on this particular system’s effectiveness and potential for widespread adoption.

The trial

Located in Castlecoole Park, Belfast, a mid-terrace house with an EPC rating of C71 was selected for the trial. The property is the first in Northern Ireland to have a hybrid solution installed. Occupied by two adults, this home faced an average outside temperature of 8.2°C between January and April 2024. An Alpha E-Tec Hybrid Heat Pump was specified, integrating an air source heat pump, combination boiler and a comprehensive monitoring system.

A heat loss study showed that the house loses 4,583 Watts of heat, meaning it needs radiators that can handle a 62°C flow temperature to maintain the required heat output. A robust monitoring system tracked key metrics such as flow rate, temperature, power and total heat energy. The E-Tec Hybrid’s performance was monitored under specific parameters: an 18°C setback temperature and a five-hour daily period at 21°C. The tenants adjusted the timings slightly during weekends to suit their needs.

During the trial, the average outside temperature ranged from -1.5°C to 18.3°C. The total heat provided to the property was 4,693.30 kWh, with the heat pump contributing 3,715.56 kWh (79%) and the gas boiler 977.74 kWh (21%).

The hybrid system demonstrated significant cost savings compared to a gas-only set-up. The total cost for heating during the trial was £510.47, averaging £4.21 per day – thus delivering a daily saving of £0.59 when compared with a gas-only system costing £580.35 (£4.80 per day).

It also delivered notable carbon savings. Compared to a kerosene oil-only or gas-only system emitting 1,453kg and 925kg of carbon respectively, the hybrid system emitted just 574kg. This represents an impressive 61% carbon saving compared to oil and a 38% saving compared to gas over the trial period.

Replicated over an average (mean) UK heating season of 5.7 months[iv], this could result in a financial saving of £102 and a carbon saving of 1.25 tonnes.

Tenants Chloe Bowman and Thomas Walker praised the system and its practicality for everyday use, highlighting its cost benefits, ease of use and reliable performance in providing hot water and maintaining comfortable indoor temperatures[v].

Advantages of hybrid heating systems:

Hybrid heat pumps are made up of two parts. The outdoor unit extracts heat from the air to heat the home, while a combination boiler works to heat hot water and boost heat in the colder months. Offering a unique and affordable solution for home heating, there are several key benefits:

  • No need to upgrade pipework
  • Operates at higher temperatures
  • Instant hot water access
  • No requirement for a hot water tank
  • Energy security through the cheapest fuel source
  • Backup support from a combi gas boiler

Alpha’s E-Tec Hybrid Heat Pump operates similarly to an air source heat pump, using a preset setback temperature to maintain a minimum internal temperature during non-heating periods. This feature enhances energy conservation and system efficiency.

With an upfront purchase and installation cost of approximately £6,500, eco-minded property owners opting for hybrid will find it 43% to 53% more affordable than a heat pump-only installation which can be anywhere between £12,000 and £15,000, depending on the size of the property.

Dan Wilden, national renewables manager for Alpha, comments: “UK homes are undoubtedly missing a trick here. Refresh NI’s trial proves that hybrid heating systems can deliver dramatically lower carbon emissions and assured cost savings on monthly bills at around half the upfront cost than standard heat pumps. This makes hybrid heating not only a more realistic step financially speaking for the average billpayer, but a solid option for a mass of UK housing stock which is in need of a retrofit solution.”

Bill Cherry, managing director for Refresh NI, says: “This has been a fascinating and insightful trial and worth the investment to provide robust evidence of the power of hybrid heating. In addition, the compatibility with combi boilers makes hybrid heat pumps a futureproof solution for home heating, having the ability to reduce carbon emissions even further when an alternative fuel is introduced into the gas network.”

Whilst solar PV and air source heat pumps have benefitted from Government grants incentivising consumers to adopt low-carbon energy on the home front, some of these schemes – such as the Boiler Upgrade Scheme (BUS) – have seen limited uptake[vi].

Alpha surveyed 2,000 UK billpayers and found that 53% of respondents would be likely to use the BUS if hybrids were included alongside heat pumps and biomass boilers. This is a very clear declaration from the British public that more households could make a transitionary step towards green heating if an incentive was available.

“The data speaks for itself and we are urging consumers to seriously consider hybrid heating as a sound choice, depending on their property type and needs,” says Dan.

[i] Latest data available. From the publication of the Climate Change Committee’s annual UK Progress Report

[ii] https://www.theccc.org.uk/publication/2023-progress-report-to-parliament/#key-messages

[iii] Decarbonising home heating (nao.org.uk)

[iv] https://assets.publishing.service.gov.uk/media/61449c5e8fa8f503bc6658dd/efus-heating-patterns-occupancy.pdf

[v] “We would definitely recommend a hybrid heat pump. From cost benefits and the easy to use system, to managing it all, it makes regulating temperature around the house easy. A main positive of using the system is the overall cost with not having to pay weekly for both gas and electric. We find it very beneficial and performs well in providing hot water and keeping the house at a good temperature.” Chloe Bowman & Thomas Walker (Castlecoole Tenants)

[vi] https://www.theccc.org.uk/publication/2023-progress-report-to-parliament/#key-messages