Heat Pump Fully Integrated with Thermochemical Store (HP-FITS)

Lead Research Organisation: University of Warwick
Department Name: Sch of Engineering


The contribution to decarbonising heat in buildings (both domestic and commercial) when utilising renewable electricity are well known and easy to appreciate. However, it is simplistic to think that with enough wind turbines, PV panels, etc. to produce renewable electricity and enough electric heat pumps to heat homes and other buildings that the problem will be solved.

Even with very efficient heat pumps the peak electricity load on a Winter's morning might be 2 or 3 times the present grid and distribution system capacity and this does not include the effect of simultaneously charging the large number of electric vehicles expected in the future.

The problem is complicated by the possibility of decarbonised gas (whether hydrogen or biogas) in a new or repurposed gas grid, partial enhancement of the electricity grid, etc.

Possible ways to mitigate these problems will include both electricity and thermal storage to manage peak loads, either at consumer level or more centralised. This proposal concentrates on heat storage, which is many times less costly per MJ that electricity storage. The concept is to store heat at the consumer's (domestic or commercial) heat pump so that the heat pump can operate when most advantageous to the system, i.e. when there is surplus renewable electricity (predominantly wind and PV). Heat is drawn from the store when there is a higher demand for or lower availability of renewable electricity. Here we consider storage times of hours to a day, but not weeks or inter-seasonally.

This is not a new idea in itself but attempts to come up with good solutions have met a number of challenges still to be solved. Prof Hewitt at Ulster has used a conventional heat pump linked to a hot water store supplying an (occupied) test house. Using signals from the Northern Ireland grid (which has a high proportion of wind capacity) the system has been operated using algorithms that would be utilised in future when the cost of electricity to the user reflected the variable production costs. This provided valuable experience in system operation and control but the overall performance was hampered by store heat losses and the limitations of the commercially available heat pump in terms of temperature output and modulation.

We will use novel storage, heat pump and control systems in an integrated package that will demonstrate how both energy and economic benefits to the user and the national energy supply infrastructure can be achieved:
Heat storage will be based on a new thermochemical absorption system that can store the required heat in a much smaller and low-loss package at close to ambient temperature.
The heat pump will combine best practice with using a variable speed compressor in a sophisticated Economised Vapour Injection (EVI) cycle to achieve a Coefficient Of Performance (COP = Heat out / Electricity in) of 5 when delivering heat at 60 C.
The control strategy will encompass the state of the grid and predicted time-variable tariffs with heat pump, store and house load models to ensure cost effectiveness combined with low emissions.

The complete integrated system will be demonstrated in Ulster University's 'Terrace House'; a new building but built as an early 1900s terrace to facilitate retrofitting of new technology in old buildings whilst occupied by 'real' people.

Planned Impact

Beneficiaries of this research include a range of different industries, government and policy makers, academia, and the general population.

Society / General Public
This research seeks to contribute to the decarbonisation of heat and hence to help counter global warming and also to reduce the cost of heating to the consumer. Thus in a global sense we will nearly all be beneficiaries and it will have a positive impact on the environment. Society should benefit from its impact on reducing future energy costs; decarbonising heating will not come without a cost implication but integrating heat pumps, thermochemical storage and grid-connected control will require less costly infrastructure (less grid capacity and fewer renewable sources needed) than other options.

Manufacturing companies that fabricate the new products and systems for heat pumping and storage will benefit from a sustained long term economic opportunity.
Companies able to undertake maintenance of the developed systems and components will have growing portfolios with increased deployment.

Government and policy makers
National and local government and policy makers will benefit from the knowledge of the major contribution that the technology will have. The knowledge and ability developed will play a major role in achieving future carbon budget targets. Policy makers and regulators seeking economically and technically viable solutions to the long term challenges of heating buildings will have a feasible option identified to reduce.

Researchers and Innovators
Researchers and Innovators in academia, industry and government, both in the UK and abroad, will gain from the breakthroughs made. This includes researchers working both in the areas immediately related to heating and those engaged in the wider energy research field including economics, policy and social inclusion.


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