The UK has set a target to reach net zero emissions by 2050. Heat accounts for nearly half of the UK's energy consumption. Among several possible solutions, heat pumps are considered as one of the most promising technologies for decarbonising the domestic heating sector. Among all heat pumps, air source heat pumps (ASHP) are the most cost-effective option for householders. the Committee on Climate Change (CCC) recommends mass deployment of heat pumps to comply with the net zero target, and their net zero 'Further Ambition' scenario includes the deployment of 19 million heat pumps in homes by 2050. However, the uptake of heat pumps in the UK is very low at present. In 2018, heat pump sales in the UK were around 27,000 units (most are ASHPs), significantly lower than other EU countries. This represents a grand challenge for the government, industry, business, and research communities.

There are a number of technological and non-technological barriers hindering the wide uptake of heat pumps, particularly air source heat pumps in the UK. There is a mismatch between the current ASHP products and the existing infrastructure and property configuration. Over 80% of houses in the UK use gas boilers for space heating, so their heat emitters (i.e., radiators) are designed for high temperature heat supply using gas boilers. However, most ASHPs available in the market have a relatively low heat production temperature. Secondly, ASHPs are vulnerable to ambient conditions. Their heating capacity and coefficient of performance drop dramatically as the ambient air temperature falls. Furthermore, frost starts to build up at the surface of the outdoor unit when the air temperature drops to around 6 C, so the outdoor units have to be regularly defrosted. Non-technical barriers have also played an important role behind the low uptake of heat pumps. The current UK heat pump market suffers from high capital cost and a low awareness of the product.

This project, based on the PI's pending patent (Application number: 2015531.3), aims to develop a novel flexible, multi-mode air source heat pump (ASHP). This offers energy-free defrosting and is capable of continuous heating during frosting, thus eliminating the backup heater that is required by current ASHPs. We will address the key technical and non-technical challenges through interdisciplinary innovations. Our project is also supported by leading industrial companies with substantial contributions (e.g. the compressor). The developed technology offers energy-free defrosting and can be operated at different modes to benefit from off-peak electricity and/or warm air during the daytime. It will be much more energy-efficient than the current products, and thus could facilitate rapid uptake of air source heat pumps, making an important contribution to the decarbonisation of the domestic heating sector in the UK.