Small Smart Sustainable Systems for future Domestic Hot Water (4S-DHW)

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


The purpose of the proposed research programme is to address the challenge of providing domestic hot water (DHW) using low carbon heat pump technology given the overwhelming trend away from conventional hot water tanks in homes and the inability of present heat pumps to provide instant hot water.

We intend to develop a suite of heat pump / storage / control technologies, using either electricity or gas that function without conventional storage cylinders and can deliver energy efficient affordable hot water to a wide range of dwellings well into the future.

Ulster will use a novel compressor being developed by industrial partner Emerson that has an exceptional range of running speeds, enabling the same device to either deliver e.g. 25 kW for instantaneous hot water or 10 kW or less for space heating. This would be used in conjunction with a small buffer store to overcome the delay in start-up before hot water is available.

Present gas fired heat pumps (both commercial and under development at Warwick) are easier to modulate but are physically large if delivering 20 or 30 kW and also have a long start up time (5 minutes). The Warwick goal is to use new composite adsorbent heat exchangers to reduce start up time to one minute, even when meeting a 25 kW load and to reduce key component sizes to achieve a compact system.

Thermal storage is a vital part of DHW provision by heat pumps. A small buffer store may be needed to overcome starting transients, or a large capacity store might be needed to provide a bath-full of water quickly. An intermediate capacity store might work together with a heat pump to meet peak loads. Our research will encompass buffers, compact PCM stores that could be sited in unused spaces such as corners in kitchens and 'flat' stores using vacuum or aerogel insulation that could fit under kitchen cabinets or other available unused spaces.

To bring this all together into a range of integrated systems suited to different housing types etc there needs to be both an understanding of the consumer's needs and preferences plus a smart adaptive control system. In addition to data in the literature we have access to data from detailed monitoring studies previously carried out by Loughborough. Consumer preferences will be investigated by the use of surveys carried out by the User Centred Design Research Group at Loughborough Design School. Ulster will assume overall responsibility for sensor choice, control hardware and software. They will devise a system controller that adapts to and meets consumer needs in an optimal way. In the long term this will be part of a house-wide wirelessly linked system including 'wet' appliances such as dishwashers and washing machines and 'smart taps' that communicate with the DHW system so that it responds optimally to the size and type of load demanded.

Planned Impact

This work addresses the 'Energy Trilema' identified by the Department of Energy and Climate Change, i.e. reducing emissions of greenhouse gases, improving security of supply (by reducing energy inputs) and improving affordability.
Its importance is highlighted by the fact that DHW accounts for 14% of heat use in the home. This compares with 63% in space heating but is much more intractable to major reduction. Present heat pump systems, whether gas or electrically driven, cannot supply instantaneous hot water in the same way as a combi boiler. We will develop new heat pump technologies integrated with advanced thermal storage to provide affordable low-carbon DHW without the need of a conventional large DHW storage tank.

Quality of Life
The research will lead to products that will result in reductions in CO2 emissions (with present energy supply infrastructure) from the current 875kg of CO2 per household per year using a gas boiler to between 625kg (electric heat pump) and 540kg per year (gas heat pump), benefitting the environment and addressing policy commitments. In monetary terms, the current annual average hot water cost is £230 and heat pumps could achieve reductions of £30 to £65 per year for electric and gas heat pumps respectively This is in addition to the savings in space heating that these same heat pumps will achieve of between £150 and £300 per annum with potential benefits in alleviating fuel poverty.

Business and Industry
The potential benefits to UK business and industry are highlighted by the TINA report on Heat which estimates the value in meeting emissions targets with heat pump systems at £12bn and in business creation £3bn. For heat pump integrated thermal stores it identifies a further £1.4bn of value in emissions savings and £1.4bn in new business creation. BSRIA's newly released heat pump study shows continued growth in the global heat pump market with the market value reaching $5.4 billion in 2014.

Although it is possible that thologies could lead to the establishment of new companies, it is more probable that existing companies working in related areas would be in a strong position to exploit. We are working with the following manufacturers who will benefit from inclusion in the research and access to its results:

The gas-fired adsorption heat pump research at Warwick will be facilitated through cooperation with BDR, best known in the UK for the 'Baxi' brand.
The electrically driven heat pump at Ulster utilises novel compressor technology developed by Emerson/Copeland to improve heat pump performance.
Spirax-Sarco is making available its vacuum insulation technology to advance thermal storage options in domestic applications.

Research assistants will benefit from working in large established research groups with excellent facilities and collaborating across different disciplines. Research assistants will be encouraged to write academic journal papers and attend and make presentations at conferences. Papers will be jointly authored as appropriate by different members of the research team across the disciplines providing exposure to different ways of working. The PI and Co-Is will benefit from undertaking and directing stimulating research and the high quality high impact publications that are expected to result.


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Hewitt N (2017) Hot water - the emerging energy challenge in International Journal of Ambient Energy