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

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.

Principal Investigator:

Professor Bob Critoph


Dr Stan Shire

Dr Zacharie Tamainot-Telto

Value: £1.30M

Start date: 01/07/20

End date: 30/06/24

Partner Institutions:

Ulster University

To find out more visit:

Interested in undertaking a PhD in thermal energy?

Dr Stan Shire and Dr Zacharie Tamainot-Telto are accepting PhD applications for funded and self-funded students.
Please email or to express your interest and find out more about our PhD opportunities.
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