Heat pumps or hydrogen boilers? Is it the right question?

Professor Simone Abram, Director of the Durham Energy Institute, assesses the clean heat technologies available to housing associations.

The end of natural gas heating

The overwhelming majority of homes in the UK are heated by natural gas combi-boiler central heating. It’s convenient, until recently was relatively affordable, has been widely accepted since the 1970s, and it is effective. It has one major drawback: greenhouse gas (GHG) emissions. And it has two further significant drawbacks – it is increasingly unaffordable and it carries a small risk of devastating harm, from CO poisoning or explosions with an average of around 200 incidents per year[1]. Government commitments to address climate change mean that the era of natural-gas central heating is coming to an end.

The question is, what’s the best alternative? Which alternative technologies could provide heat to homes and businesses without GHG emissions, with low risk, and are affordable and convenient? Much of the recent government focus has been on heat pumps versus hydrogen, but there are many other options to consider. Now is a good time to ask if these two options are the answers to the right question.

How to choose a new heat infrastructure

First, it’s important to note that heating needs and opportunities are not uniform. Different parts of the UK may be best served by different forms of infrastructure at different times. Second, the key question is how to make indoor spaces comfortable and affordable, so the focus needs to be on heat, not fuel or energy source. The one universal about heat is that the temperature of a space will always revert to ambient. In other words, to heat a space effectively, that space must be well-insulated as well as suitably ventilated. In spaces that are not heat-retentive, there is an option to heat the person rather than the space, such as using underfloor heating, radiative heating, and warm clothes as important and often-overlooked ingredients to the provision of comfort.

Where space heat is required, it’s worth considering how to make choices about changing infrastructure. A recent Interreg (EU inter-regional) research project identified a set of principles that should govern the choice of heating (and cooling) infrastructure based on a combination of environmental, economic, social and ethical arguments. These 5 principles could help transform approaches to energy efficiency and home improvement[2]:

1. Close the loop (prevent heat waste);
2. use low-grade sources for low-grade demand (e.g. use waste heat for heating, fuel for power);
3. decentralized and demand-driven energy supply (avoid circulating heat that’s not needed);
4. integrate energy flows (to get cross-benefits between energy supplies);
5. prioritise local sources (save on transport losses and infrastructure investments);

These principles would lead us to a rather different picture of heating infrastructure than the one we have today – one that would be more efficient, less costly, more fair. The second and last also help to show how to prioritise alternatives.

Heat is comfort

Together, they suggest that a UK heat-strategy should prioritise heat networks in urban areas, supplying heat rather than fuel. With a network in place, the source of heat can be relatively simply interchanged. A heat production hub could be fuelled by hydrogen, by green electricity, by geothermal heat or high or low grade (ie high or low source temperature) with a combination of central and local heat pumps. Rather than replacing gas boilers with hydrogen boilers, a local heat pump could be installed to allow home owners to adjust the temperature in their own dwelling according to their needs. This has already been done in a number of apartment blocks across the country.

The potential to simply replace Methane in the existing gas infrastructure with Hydrogen is appealing, because it demands the least disruption to most users, just a local adjustment to the existing boiler. Hydrogen is also safer – less explosive and less poisonous than natural gas. Testing is currently ongoing to see how hydrogen behaves in the gas transmission system, how and where it leaks, and what effect this has. Early results are promising, on the technical side, although the economics remain unclear. Among hydrogen researchers, however, the idea of burning hydrogen in the home for domestic heating is increasingly regarded as a waste of a high-value energy-source. Hydrogen will be in demand for energy storage and for transport fuel, and production will be limited for some years.

On the other hand, air-source or ground-source heat pumps are expensive to install for a single dwelling. Collective systems with small localised heat exchanges have more promise. Again, this points towards the importance of heat networks for efficient and affordable comfort. New research is exploring whether hydrogen could be part of local ‘combined heat and power hubs’, where hydrogen is produced either for power or for transport fuel when there is excess renewable electricity, and the waste heat from energy production feeds into a local heat network. Only the most isolated settlements or off-grid dwellings require individual heating systems, and in this case a combination of insulation, solar thermal or PV, with air or ground source heat pumps is most likely to be effective.

There are other significant sources of heat in the UK, from the waste heat produced by industry (not least from data centres), or the heat held in the water that fills some of the 23,000 abandoned coal mines across the regions. These have been estimated to have sufficient heat to supply all of the houses in the UK for a century or more[3].

All of the options will require investment. But the Committee on Climate Change, and Carbon Tracker, have long calculated that this investment will be far less than the cost of adapting to climate change. The challenge now is to invest wisely and to future-proof the investments.

[1] See https://www.gems.ac.uk

[2] See https://www.hse.gov.uk/statistics/tables/ and https://www.co-gassafety.co.uk/information/co-gas-safetys-statistics-of-deaths-and-injuries/

[3] See https://5gdhc.eu/5gdhc-in-short/