Low Temperature Heat Recovery and Distribution Network Technologies
Introduction
LoT-NET was a six-year EPSRC GrantLink opens in a new window programme awarded to Warwick in 2018 to investigate how waste heat could be recovered, used and incorporated in smart, thermal and electrical energy systems.
Heating and cooling produces more than one third of the UK's CO2 emissions and represent about 50% of overall energy demand. BEIS anticipate that heat networks could supply up to 20% of building heat demands by 2050. Heat networks have previously used high temperature hot water to serve buildings and processes but now 4th generation networks seek to use much lower temperatures to reduce heat losses and to enable heat pumps to operate efficiently.
LoT-NET examined ways in which CO2 emissions due to heating can be reduced or eliminated by using low temperature networks to connect recoverable heat sources, thermal stores, heat pumps and buildings. The overall principle was to address 4 areas:
- What is the decarbonised heat source? What are the alternatives and decisions?
- How to include thermal storage?
- How to include waste heat recovery?
- How to reduce demand?
The strategies include:
- Taking advantage of the slow cool-down rate for modern, well insulated buildings by delivering heat throughout the day and night, as opposed to a traditional rapid heating in the early morning. This will:
- reduce the peak electrical demand from the grid
- allow installation of smaller and cheaper heat pumps
- allow a reduced heat emitter temperature, such that heat pumps achieve higher COP
- Operate existing building management systems (BMS) with greater oversight to ensure operation “as planned” without corruption of system settings, thereby avoiding unnecessary heating
- Use multi-zone heating controls and sensors to apply heating only where needed
- Improve building fabric standards. Provide large-area heat emitters so that heat pumps can operate at low temperature lift and achieve high COP.
- Use a low-temperature network to connect recoverable heat sources, heat pumps, large thermal stores and buildings.
- The "recoverable heat" is typically not at a high enough temperature to provide direct heating but acts as a heat source for the heat pumps, thereby reducing the temperature lift and increasing COP. Heat pump COP as high as 9 were achieved.
- Use very large thermal stores to utilise renewable energy at times of low demand and then provide heat with little or no electrical requirement during cold, low-wind periods.
The LoT-NET case studies provide evidence to guide strategic decisions at a national level in terms of heat network expansion, heat pump COP targets, planning for large thermal stores (to minimise operating costs and reduce the requirement for large-scale electricity storage) and the use of recoverable, low-temperature heat sources to raise heat pump COP.
Heat networks and very large stores will be permanent parts of the national infrastructure, with long payback periods. These will require large-scale plannning and incentives to encourage development and expedite the UK's Net Zero target.Project Outline
The original plan was for an interdisciplinary collaboration between the four Universities (University of Warwick, Loughborough University, London South Bank University and Ulster University), but this became impractical due to COVID-19 and the associated lockdowns and travel restrictions.
It is notable that to date, smart thermal networks are less well understood than smart power networks, although significantly more energy is used in our homes and businesses as heat rather than electricity. The programme addressed these issues through a focus on how waste heat (and cold) can be recovered and used, for example by incorporating low carbon energy resources in smart, thermal and electrical energy systems.
The four universities carried out a series of case studies into technologies required for the adoption of Low-Temperature Networks. The aim was to identify best practice in each area, leading to recommendations for policy development and strategic planning as part of the UK’s commitment to Net Zero by 2050.
University of Warwick:
- Studies into the operation and optimal control of buildings connected to a heat network.
- Development of an adsorption heat pump and thermal transformer to use heat more efficiently.
London South Bank University:
- Identification of sources of recoverable heat that would reduce the electrical power required by heat pumps.
Loughborough University:
- Simulations and experimental work into thermal stores at both small scale (domestic) and very large scale. This allows heat pumps to run whilst electricity is cheapest and even for seasonal storage to obviate the need for electrical power during periods with no wind.
- Consumer surveys into the acceptability of low-carbon heating measures.
Ulster University:
- Development of advanced heat pumps with variable output, high COP and high delivery temperature for ease of retrofit or industrial use.
Project partners: 3D Technical Design Ltd Asda Causeway Coast & Glens, Dept for Bus, Energy & Ind Strat (BEIS), Emerson Climate Technologies GmbH, FutureBay, Greater London Authority (GLA), Islington Council, London Underground Ltd, REHAU Ltd, Spirax sarco, SWEP International
