HEAT NETWORKS | WASTE HEAT Wasted opportunity If the UK reused waste heat from its buildings and industrial processes, it could be used to supply 14% of the hot water and heating demand in UK homes, says FairHeats Lina Agln S o much heat produced in the UK is going to waste. The list of culprits is long: food industries, cement factories, warehouses, leisure centres, sewage plants and waste-incineration sites are among the facilities producing heat that is not used but it does not have to be that way. In Sweden, there are several examples of waste heat being reused to produce heating and hot water. The use of waste heat is enabled by the countrys district heating infrastructure, which, in 2016, supplied more than 57% of all buildings in Sweden with heat and hot water. Based on statistics gathered from Swedish district heating producers, more than 45% of all the heating generated in 2018 came from sources of waste heat. District heating, often referred to as a heat network, relies on a network of pipes to transport heat to individual buildings and dwellings from a centralised source of production. Heat exchangers in individual buildings and/or dwellings extract heat from the hot water, and this is then recirculated as cool water to the central production. The source of heat at the central production varies. It can be a boiler or combined heat and power (CHP) system, but it can also be a heat pump or a heat exchanger. These last two examples are highly relevant for waste heat. I work for a specialist consultancy dealing exclusively with heat networks. As part of my role, I visit existing developments with heat networks, as well as developments under construction. In many cases, the new developments are built with natural gas-based heat networks, despite being next door, literally, to a facility that is generating waste heat. Given the significant impact it has had on heating provision in my native country, I cant help but wonder why more effort has not been made to use waste heat in the UK. As the potential for waste heat in the UK energy system is largely unknown, I prepared a case study for the CIBSE Technical Symposium that aims to create a basis for discussion around the potential for waste heat in the UK. Incorporating unutilised waste heat into district heating production1 investigates what effect using Swedish techniques for waste-heat recuperation would have on the UK heat supply and its associated emissions. According to a report from the Department for Business, Energy and Industrial Strategy, published in 2018, net UK emissions in 2016 amounted to 468Mt CO2e. Heat demand is the biggest source of the countrys carbon emissions, with about 46% of the heat demand used for space heating and cooling. Figure 1 displays the breakdown of 2016 UK carbon emissions across sectors. To recuperate waste heat from industries, heat extraction can be made possible via a heat exchanger. For industries outside of the metallic, mineral and chemical sectors, the majority of waste heat potential is available in the temperature range of 100C to 200C, which is suitable for recuperation into district heating production. An estimated 9TWh of waste heat in this temperature range is currently unused in the UK industrial sector.1 One potential approach to recuperating waste heat created in dwellings is through using heat in wastewater. Warm wastewater is created from everyday activities such as showering, washing hands and cleaning 2020 PAPER D ACCEPTE Technicalm Symposiu .org/ www.cibseum symposi UK emissions in 2016 across different sectors 50% Percentage 40% 30% 29% 20% 17% 10% 0% 6% 18% 15% 9% 2% 4% n Transport n Agriculture and waste n Buildings and Industry (non-heating n Other n Heat industrial processes n Heat cooking n Heat hot water n Heat space heating (and cooling) Figure 1: Breakdown of 2016 UK carbon emissions across sectors 38 May 2020 www.cibsejournal.com CIBSE May20 pp38-39 Supp Waste heat.indd 38 24/04/2020 16:32