Written by Dr. Kevin O’Toole
Decarbonising heat is a major challenge we need to address as we strive to achieve our net-zero targets. Heat pumps are a much better heating solution than gas boilers, providing greater energy supply resilience, lower cost, and less global warming.
They are much more efficient than gas boilers (at least 300 percent compared to about 85 percent); a recent analysis found that, at post-April 2022 prices, a heat pump of the legal minimum efficiency can save up to 27 percent or £261 a year on heating bills compared to a gas boiler. They can be powered by green electricity which does not contribute to global warming. The national grid is becoming increasingly green.
Of the alternatives to natural gas, renewable methane from biological sources will only ever be able to contribute a small fraction of heating in the UK, and hydrogen will be more expensive than natural gas.
So we need heat pumps, but they have their own issues which need to be addressed.
A heat pump costs more than a boiler so is a barrier in many people’s minds. However, if the purchase and operating costs of heat pumps and boilers could be spread over a number of years, heat pumps are now cheaper, as the same recent study said. Just as you don’t pay a lump sum for the cost of a power station when you switch electricity suppliers, it pays to seek out deals that don’t ask you to pay upfront.
Another issue is the inability of heat pumps to deliver the higher temperatures for which the radiators in many homes and offices are designed. This is actually not a real problem for most days of the heating season, when temperatures in the range 45-55°C, deliverable by most heat pumps, are adequate. On the coldest days, a solution offered by many brands is a backup of a resistance heater (efficiency 100 percent). This is also needed for storing domestic water, which should be at 60°C or above to kill any bacteria which might be present.
An important issue that is not apparent to customers is the impact of the refrigerant fluids used in current heat pumps. Most of these have a global warming effect between 100 and 750 times that of carbon dioxide if they escape to the atmosphere, which 2 percent of them (by weight) do every year in homes, and 6 percent in office aircon systems. Other refrigerants with lower global warming effects are gradually replacing these over the next 13 years, but these also leak at the same rates and have challenges in terms of either cost, flammability, or toxicity, needing controls and annual maintenance, including re-gassing. In addition to releasing greenhouse gases, leakage also reduces the efficiency of the heat pump which increases the costs of running them.
Alternative heat pump technologies are in development that improve on current products and overcome their weaknesses. The leading alternative uses a metallic alloy that releases a lot of heat energy when compressed, and then returns to its original shape and cools when the pressure is released. This cycle can be repeated for a long lifetime of 20-30 years with similar efficiencies compared to most current heat pumps. This lifetime is longer than current heat pumps. Importantly, this solid-to-solid cycle does not use the refrigerants needed by the current liquid-gas cycles in heat pumps, therefore eliminating their contribution to global warming and the associated maintenance costs. As it is a metal, it doesn’t leak, so there are no issues around reduced efficiency and increased running costs. It will also be able to deliver the higher temperatures on relatively few cold days, at a lower efficiency but without the need for a backup system.
Finally, heat pumps can deliver your heating in the winter and cooling in the summer, something that the gas boiler will never do. Watch out for this technology in the coming few years.
About the author
Dr. Kevin O’Toole is Co-founder and Managing Director at Exergyn.
Exergyn is a clean energy tech producer based in Glasnevin, Dublin, that specialises in the design and development of unique solid-state shape memory alloy (SMA) technologies for commercial use. The groundbreaking company is on a mission to curb climate change through producing technology that replaces the release of destructive refrigerants into the atmosphere through existing systems, with a more efficient clean solid-state system. Exergyn is developing a cleantech saving grace, an efficient and affordable emission-free solution. It employs 33 specialist staff across Dublin, the UK, the US, France, Germany and Prague. For more information visit https://www.exergyn.com/