Heat pumps reviewed

Heat pumps run like refrigerators in reverse. Instead of pumping heat out of sealed box, they pump heat from outside a building into it. And crucially they use electricity to do this very efficiently, much more so that just by using the electricity direct for heating.   The UK government is keen for all home owners to move over to using heat pumps. However, only 0.8% of UK homes have a heat pump at present. Last year just 30,000 heat pumps were installed in Britain. In contrast, according to Andrew Warren from the British Energy Efficiency Federation, around 1.6 million new condensing gas boilers were put in. We are going the wrong way.

According to the Committee on Climate Change, 19 million heat pumps will need to be installed by 2050 to reach net zero emissions, and hybrid heat pumps (with gas boiler back up) will need to be widely used by 2035. But the UK Energy Research Centre recently suggested that, on its current trajectory, it will take the UK 700 years to transition to low-carbon heating this way! In addition, the electrical grid may need to be significantly expanded to facilitate the extra power capacity that using heat pumps rather than gas will require. That will add to the already relatively high cost of domestic heat pumps compared to gas boilers. So, although heat pumps do have the attraction of sometimes being able to use power 3-4 times more efficiently than direct heating systems, there are some issues. The House of Commons Environmental Audit Committee is to look at them in a new review.

One thing it should look at is scale. Large-scale heat pump projects are more efficient /cost effective than domestic scale units, and although the latter are being pushed strongly, there is also a new allocation of Tariff Guarantees in the Non-Domestic Renewable Heat Incentive (RHI), supporting larger projects, including large scale ground source heat pumps >100kWth. That is to be welcomed.

However, the Non-Domestic RHI will close to new applicants in March 2021. BECC have consulted on a new Clean Heat Grant, scheme, with a proposed cap on the capacity of eligible appliances of 45kW. In Oct last year Energy & Business Secretary Kwasi Kwarteng said it ‘will provide targeted support to consumers and small businesses for heat pumps and some limited biomass from April 2022’. It’s backed with £100m, as announced in the 2020 Budget, and will be open for 2 years. 

Meanwhile, the lobbying for domestic-scale heat pumps, as opposed to hydrogen-fired boilers for home heating, continues. A  review of hydrogen use by a group of experts, in the web magazine Conversation, included a paper by Petra de Jongh, Professor of Catalysts and Energy Storage Materials, Utrecht University, who was not impressed. He said that ‘one kilowatt-hour (kWh) of electricity in a heat pump may generate 3-5 kWh of heat, while the same kWh of electricity gets you only 0.6-0.7 kWh of heat with a hydrogen-fuelled boiler’. 

However, that does take the best case for heat pumps, as if that will be the norm. How often will a heat pump attain a COP (Coefficient of Performance) of 5 or even 3, in practice- in winter? And how will we meet peak heat demand then? All we are told is that ‘because heat pumps need so much less energy overall to supply the same amount of heat, the need for large amounts of stored green energy on standby is much less’. True, but we will still need some and a delivery system to meet heat demand peaks especially. Hence the hybrid heat pump/hydrogen boiler idea, with a gas link retained. And not just for ‘particularly old homes’, as the article suggests: fitting heat pumps may be hard in many homes. 

The debate over heat pumps and hydrogen goes on. It is now harder to sustain the view that home heat pumps should only be used in off gas grid areas, but, with the best will in the world, it will take time to strip out all the existing gas-fired central heating boilers and replace them with hybrid heat pumps. Moreover, as the Conversation article accepts, they will be expensive to install. While green hydrogen is getting cheaper- and its use for heating would reduce the stress on the power grid, as has been recognised in the plans for hybrid heat pump/gas boilers. 

There is also the issue of scale. The Conversation article also looked to larger-scale heating systems, linked to local heat nets, and as noted above, larger heat pump systems can be more efficient. And that is on the way. BEIS expects ‘several large-scale heat pump projects to receive financial support’ through various schemes, including the Green Heat Network Scheme, and the Industrial Energy Transformation Fund, which is open to large heat pumps providing process heat. 

Certainly, big municipal-scale heap pumps can be good, including those using rivers as a heat source, and district heating systems fed by gas fired Combined Heat and Power plants can have COP equivalents of around 10! They could also use heat stores- and a bit of solar topping up might also be possible. There is also the option of large scale gas fired heat pumps- and they could use biogas. 

Plenty of routes ahead then…not just domestic electric heat pumps and not all of them abandoning the gas mains, currently the source of most of the UK’s heat energy. Though the government is still toying with the idea of banning new gas connections to new houses at some point. A 2023 deadline for implement of the ‘Future Homes Standard’ for new homes, ‘with low carbon heating and world-leading levels of energy efficiency,’ was mentioned initially, later adjusted to 2025, but then the White Paper on Energy said the government wanted to be flexible on the extent and the pace. There will be a consultation on this, although the aim was still to get it sorted ‘as soon as possible’. It could certainly be a big costly change, with air source heat pump installation costing around £6000 - £8000, and ground source heat pump installation £10,000 - £18,000, depending on the amount of heat required.