If you were planning to move, build, or renovate your house and were given a choice of what fuel to use for your central heating and hot water demand, what would you choose: air source heat pump, ground source, natural gas, oil or biomass? There is a wide range of heating solutions on the market and the recent energy ‘spike’ has made consumers more energy-aware as we look to a Net Zero carbon future.
What option is realistic and affordable today?
As Northern Ireland looks forward to a heat consultation in the summer months, many pundits are suggesting we need a range of technologies, and that all low-carbon pathways should be explored.
In GB and the Republic of Ireland, both governments are proposing an all-electric future, with air source heat pumps (ASHP) being promoted as the preferred option and district heating in urban areas. In the author’s opinion, an ASHP is an ideal product for a new build or thermally efficient house, but with 70% of bungalows, 50% of semis, 53% of detached and 44% of terraces in Northern Ireland being in SAP Band D – G, the question remains: will these houses be suitable for a heat pump?
Many will claim they will, but with Governments’ data showing that retrofitting or upgrading insulation and installing a heat pump will cost anywhere from £23K to £30K, and with consumer finance at a real-time low, is this really a viable option for the approximately 500,000 homes currently using oil and circa 200,000 using natural gas in NI?
Taking the plunge into HVO
One consumer in Ballyfrenis, Millisle, believes that low-carbon liquid fuels and off-peak battery storage are the answer. He has taken the plunge and converted his new liquid fuel boiler to run on a renewable liquid biofuel called hydrotreated vegetable oil (HVO). The solution was designed by NextGen Power, and London-based Green Biofuels Ltd. GBF supplied the advanced HVO fuel, called GD+, which is made from renewable waste cooking oil and reduces CO2 equivalent emissions by up to 90%.
As part of the project, the hot water is hydraulically separated from space heating and supplied by a solar-assisted heat pump. This allows the boiler to operate in condensing mode all the time. The client has also added 4.5kW of solar PV linked to battery storage in the garage. He charges the battery pack overnight and any excess is exported back to the grid.
The new homes in Ballyfrenis were completed in 2022 and are built to a high energy efficiency specification. A biofuel-ready condensing boiler was already in place and air permeability is 6.7 m³/h.m², which is average. The EPC on completion was B86, which is very good but that was before the fuel change and the addition of solar.
How ‘carbon-friendly’ is this house?
We have modelled the emissions on kerosene and grid electricity, and, for this exercise, we have assumed a space heating demand of 9,000 kWh, hot water demand of 3,000 kWh and a further 6,000 kWh of general electric use. This provides a projected annual carbon emission total of approximately 6.3 tonnes. This is made up of 4.5 tonnes for space heating, 1.125 tonnes for hot water and 1.80 tonnes from the grid.
By using HVO in the model for space heating, it is possible to reduce the carbon emissions to 0.48 tonnes per annum. With the hot water being provided by the solar-assisted heat pump, the emissions are reduced to around 0.18 tonnes. For general electrical requirements and utilising the 4.5 kW solar PV generation and an assumed load factor of 0.1, we can assume approximately 4,000 kWh from solar energy over the year, leaving a 2,000 kWH requirement from the grid. This results in about 0.6 tonnes of CO2 from general electric use.
Utilising HVO and solar energy, we are estimating a total carbon emission of approximately 1.14 tonnes: that is a reduction of over 5 tonnes of CO2 or an 88% reduction in the overall carbon footprint! The revised EPC (incorporating the fuel change and solar energy) moves from a B85 rating to an A96 one, which is extremely high. The average energy rating in Northern Ireland is D60 for reference.
OFTEC oversaw the boiler conversion, and the project is being monitored by Dr Patrick Keatley of NEMO Energy Limited. Looking at the figures, he commented, “With HVO emitting 0.036 kgCO2/kWh compared to kerosene at 0.298 kgCO2/kWh, we can achieve a substantial reduction in the carbon footprint immediately. Adding in the benefits of the solar-assisted heat pump for hot water, along with battery storage, we can estimate a decrease in carbon emissions to 1.14 tonnes, which is almost 90% lower than the original footprint using kerosene and 100% grid electricity. We will be monitoring the property over the next 12 months and confirm the findings at the end of the year”.
In terms of CO2 emissions, an HVO-fired boiler can deliver the most rapid and significant reductions and requires the least behavioural change by customers. While there are challenges around cost and supply at scale, it is clear that HVO could be an effective decarbonisation solution for energy-efficient, liquid-fuelled homes in the future. Government support for HVO as a low-carbon heating solution could make it a relatively straightforward and cost-effective option for decarbonising liquid-fuelled homes today.
