High-Performance Heat-Powered Heat-Pumps (HP3)

Lead Research Organisation: University of Nottingham
Department Name: Faculty of Engineering

Abstract

The UK has made considerable progress decarbonising its power sector. However, decarbonising space-heating has been much more challenging. Currently, space-heating accounts for ~1/3 of the country's CO2 emissions. This must change to achieve Net Zero

Two main low-carbon heating solutions are being considered: 1) direct heating from hydrogen combustion in boilers and 2) electrically-driven heat-pumping. Although both are promising, there are serious challenges to overcome.

National Grid and other gas network operators have confirmed the technical feasibility of distributing hydrogen through the existing gas infrastructure, which connects >23 million properties. Hydrogen boilers are not commercially available yet, but they are well underway. Hydrogen can be made from renewable electricity; however, a big downside is that when combusted in boilers, the amount of energy we recover is only ~60% of what we spent making it. It is not a very efficient process.

Electric heat pumps have a much higher efficiency. The amount of heat they provide can be as much as 3x the amount of electricity they consume. So, for every 1kWh of electricity used, a heat pump will give 3kWh of heat. This in stark contrast to the 0.6 kWh that would be obtained if the same 1kWh of electricity was used to make hydrogen, and that hydrogen was combusted in a boiler.

Although it seems like using electric heat pumps is the way to go, there is a major problem. The electricity grid does not have the capacity to support their use in any significant fraction of UK homes.

The reason for this is the huge energy demand for heating purposes. During winter, the peak demand in the gas network is more than 4x than the peak demand in the electricity grid. But also, during the first few hours of each day, the gas network experiences power-ramps that are 10x greater than what the electricity grid sees. The electricity grid does not have the capacity to provide the same levels of energy and power as the gas network. The upgrades required to enable the electricity grid to take on the gas network's duty are too expensive to be viable.

It is precisely these challenges that are holding back the UK's transition to low-carbon heating.

This postdoctoral fellowship addresses this issue by investigating and developing a deep understanding of a novel set of technologies called 'High-Performance Heat-Powered Heat-Pumps (HP3)'. These innovative heating systems combine the best attributes of the two main low-carbon options being considered (hydrogen boilers and electric heat pumps) and at the same time, removes their drawbacks.

The widespread adoption of HP3 systems will enable the gas network to distribute hydrogen to homes across the country and therefore to continue to supply the enormous demand for energy during winter. HP3 systems deliver a greater benefit per unit of H2 consumed in comparison to hydrogen boilers. This will help the gas network to supply hydrogen to even more homes but also, consumers will enjoy reduced bills. By keeping the gas network in service, the use of HP3 systems will avoid placing an overwhelmingly large load on the electricity grid that would be created if the country adopted electrically-driven heat-pumping.

This fellowship will develop detailed computational models to simulate the operation of HP3 systems in order to understand the effect that different design and operational variables have on their performance. Special focus will be given to exploring ultra-high operating pressures at this can lead to reductions in the overall cost of the units. A laboratory prototype will be developed and tested to demonstrate the functionality concept.

This work has real prospects to be transformational in two different ways: (i) triggering a step-change in the UK 'boiler industry' towards more sophisticated and much higher-value products and (ii) accelerating the achievement of Net Zero by improving affordability.

Publications

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