Water
retrofit or replacement of existing systems, our research indicates that gas-fired water heating continues to dominate. Over the course of five years (2019-2023) it accounted for 88 per cent of recorded installations across the sector, making it by far the most popular choice for supplying heating and hot water demands. With low-carbon new builds accounting for just 0.6 per cent annually of the total care home built estate in the UK, the scale of the challenge becomes clear. Although all lower carbon technologies (electric water heating, heat pumps, and solar thermal) are showing increasing specification, adoption rates have remained generally low. Of these low-carbon technologies, ASHPs have exhibited a more rapid uptake in the past two years, but the number of sites deploying the technology remains lower than expected and are almost exclusively associated with new build. When questioning consultants and contractors, heat pumps will always be specified for heating, but most are realising that heating and hot water in many cases are best left separate, which from a design perspective makes absolute sense.
The real cost of net zero
Due to building regulations, renewable, all-electric hot water systems are being specified for new build, but when dealing with retrofit, the majority of those questioned confirmed that while initially leaning toward heat pumps, they were encountering problems with cost, infrastructure, and design. The cost has been a particular hurdle for the sector, not only in terms of capital
investment, but especially concerns over operational costs which climb when transitioning to electricity. At the time of writing, gas costs 5.48p per kWh (kilowatt hour), versus electricity at 22.36p per kWh, which can lead to substantial increased operating costs, especially given the typical daily high demands for hot water. It is also worth remembering that a considerable proportion of grid electricity (around 20 per cent) is generated by gas-fired power stations. Should gas prices climb, so too will grid electricity prices. This will continue to be the case until the grid is fully green. Hence the interest in energy independence, which is obtained using true renewables such as wind and solar. Heat pumps, however, are not a ‘true’ renewable technology, despite being cited and pushed at the highest levels of government as a ‘renewable technology’. ASHPs are without doubt one of the easier to implement technologies, using a reverse refrigerating circuit to extract heat from the air, even when ambient temperatures drop during the winter months. The efficiency of a heat pump is measured by its COP (coefficient of performance) which defines how much energy it uses compared to the heat energy it generates. The higher the number the better. The COP will fluctuate with external temperatures, so the seasonal COP which averages the efficiency across the year is a better means of assessing a unit’s potential. As the ambient temperatures drop, the heat pump will demand more electrical energy to run the compressor and maintain necessary output temperatures. This is where heat pumps have a weakness, as they were designed to operate at low working flow temperatures (35°) to supply radiators and underfloor heating, rather than the more stringent requirement of heating water to +60°C to prevent legionella. This additional electrical energy
required to raise temperatures will typically come from the grid. This means building in sustainability with ASHP technology
January 2025
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alone can deliver considerable increases in operational costs if not approached with care and consideration. Of more concern is that electric water heating can place a significant additional load on a building’s electrical system.
For buildings with substantial electrical usage, adding high-demand electric water heaters and heat pumps can strain the system. From our experiences, we are already seeing projects adding extremely costly upgrades to electrical infrastructure as part of refit – something better hot water design could help avoid. As a result, specifications are being revised back to gas when connections are available. Reasons cited in our research for
reverting to gas included it being much simpler, familiar, and cost-effective to replace and run. New generation appliances were seen to be more efficient, with lower carbon and NOx emissions. Most are also 20 per cent hydrogen-blend ready out of the box, and so offer a future-proof option for the next 15 to 20 years.
Staying hybrid
While heat pumps do have a valid role to play, for water heating they need to be used as part of a wider process to ensure cost-effective, efficient operation. Known as hybrid water heating, the approach is particularly relevant to buildings in which there is already a gas connection. Hybrid systems will require two heat generators and two energy connections, one of which being an environmental heat source such as an ASHP for preheating cold water up to 55°C as it flows into the system. This is more than achievable for most heat pumps using current R-32 refrigerant. There are ASHP units capable of higher +70°C temperature outputs which use propane as a refrigerant. While attractive on paper, the initial generation of products in this class are larger, heavier, and more costly. In trials, efficacy at lower ambient temperatures drops steeply, meaning greater electrical
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