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.

The cooling sector currently consumes around 14% of the UK's electricity and emits around 10% of the UK's greenhouse gases. Global electricity demand for space cooling alone is forecast to triple by 2050. Moreover, as air temperature increases, the cooling demand increases, but a refrigerator's Coefficient of Performance decreases. This results in a time mismatch between a refrigerator's efficient operation and peak cooling demand over a day. Clearly, this problem will deteriorate over the coming decades. Indeed, research by UKERC recently reported that cooling sector will cause a 7 GW peak power demand to the grid by 2050 in the UK. A solution is to employ cold thermal energy storage, which allows much more flexible refrigeration operation, thereby resulting in improved refrigeration efficiency and reduced peak power demand. Large-scale deployment of cold thermal energy storage could dramatically reduce this peak demand, mitigating its impact to the grid. Moreover, the UK curtails large amounts of wind power due to network constraints. For example, over 3.6TWh of wind energy in total was curtailed on 75% of days in 2020. Therefore, through flattening energy demand, cold thermal energy storage technology provides a means to use off-peak wind power to charge cold thermal energy storage for peak daytime cooling demand. This project, based on the proposed novel adsorption-compression thermodynamic cycle, aims to develop an innovative hybrid technology for both refrigeration and cold thermal energy storage at sub-zero temperatures. The resultant cold thermal energy storage system is fully integrated within the refrigerator and potentially has significantly higher power density and energy density than current technologies, providing a disruptive new solution for large scale cold thermal energy storage. The developed technology can utilise off-peak or curtailed electricity to shave the peak power demand of large refrigeration plants and district cooling networks, and thus mitigates the impacts of the cooling sector on the grid and also reduces operational costs.

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.

The cooling sector currently consumes around 14% of the UK's electricity and emits around 10% of the UK's greenhouse gases. Global electricity demand for space cooling alone is forecast to triple by 2050. Moreover, as air temperature increases, the cooling demand increases, but a refrigerator's Coefficient of Performance decreases. This results in a time mismatch between a refrigerator's efficient operation and peak cooling demand over a day. Clearly, this problem will deteriorate over the coming decades. Indeed, research by UKERC recently reported that cooling sector will cause a 7 GW peak power demand to the grid by 2050 in the UK. A solution is to employ cold thermal energy storage, which allows much more flexible refrigeration operation, thereby resulting in improved refrigeration efficiency and reduced peak power demand. Large-scale deployment of cold thermal energy storage could dramatically reduce this peak demand, mitigating its impact to the grid. Moreover, the UK curtails large amounts of wind power due to network constraints. For example, over 3.6TWh of wind energy in total was curtailed on 75% of days in 2020. Therefore, through flattening energy demand, cold thermal energy storage technology provides a means to use off-peak wind power to charge cold thermal energy storage for peak daytime cooling demand. This project, based on the proposed novel adsorption-compression thermodynamic cycle, aims to develop an innovative hybrid technology for both refrigeration and cold thermal energy storage at sub-zero temperatures. The resultant cold thermal energy storage system is fully integrated within the refrigerator and potentially has significantly higher power density and energy density than current technologies, providing a disruptive new solution for large scale cold thermal energy storage. The developed technology can utilise off-peak or curtailed electricity to shave the peak power demand of large refrigeration plants and district cooling networks, and thus mitigates the impacts of the cooling sector on the grid and also reduces operational costs.

Decarbonisation of the UK's energy system will require substantial action at a regional and local level. Therefore, the UK's energy system is growing rapidly to a more decentralised model by 2050 with a great level of small-scale electricity and heat generation at the distribution level, where wind and solar renewable energies will play a large role. However, the intermittent nature of these renewable sources presents a great challenge in energy generation and load balance maintenance to ensure stability and reliability of the power network. This highlights the need for electricity storage technologies as they provide flexibility to store excess electricity for times when it is in demand. The majority of recent installations deploy fast response electricity storage systems (e.g. batteries) with short-duration electricity storage (minutes-days) and short-discharge duration of up to 4 hours. However, technologies with long-duration electricity storage (days-weeks) and medium-duration discharge of over 4 hours, with negligible capacity and efficiency degradation are required to ensure power supply security in all weather conditions (e.g. wind or solar energies are not available for several days). There are several possible technologies for long-duration energy storage, e.g., pumped-hydro storage, liquid air energy storage and compressed air energy storage (CAES). Among them, adiabatic CAES systems (ACAES) has the lowest installed energy capital costs (2-50$/kWh) for a wide range of storage applications from micro scale (few kW) to large scale (few MW). In conventional ACAES systems, the electricity is used to compress air in compressors, generating high levels of heat during the process. The heat of the compressed air is removed at the outlets of the compressors and stored in a thermal energy storage (TES) unit, while the cool compressed air is stored in a cavern at depths of hundreds of metres. To discharge the energy on demand, the cool compressed air heats up in the TES before expansion in turbines to generate electricity. Despite its promising features for decarbonising the electricity power system, there are major challenges which hinder further development of ACAES systems, including (1) limitations on the underground geology, (2) low roundtrip efficiency and (3) thermal and structural challenges on the TES unit because of high-temperature air at the outlets of the compressors. This proposal aims to address these major challenges through development of an affordable micro-scale co-generation near-isothermal and adiabatic CAES system with overground air storage vessels (micro-Ni-ACAES). The system utilizes near-isothermal and high-efficiency compressor/expander devices, TES and heat exchanger units based on an innovative composite phase change material and air storage vessels. The project will perform a fundamental experimental and modelling analyses to gain deep insight into the flow and thermal fields in the near-isothermal compressors/expanders as well as charging and discharging kinetics of the TES unit. Both isochoric and isobaric storage processes will be analysed. These fundamental studies will lead to efficient designs of the micro-Ni-ACAES system components and further support the development of a thermodynamics-based design tool. The design tool will be used to identify the system's optimum operating condition and control strategy for steady-state and dynamic operations of the system. Additionally, the project will include a techno-economic and environmental impact assessment in order to evaluate the economic viability of the system, as well as CO2 abatement and fossil fuel savings over the system's lifetime. The proposed high efficiency co-generation micro-Ni-ACAES systems are believed to be the future of the CAES technology, eventually culminating in decentralised microgrid power network in application to district energy network or commercial sectors (e.g. business parks).