Heat Pumps Today

24 February | March 2023 T E C H N I C A L HEAT NETWORKS EXPLAINED There are over 14,000 heat networks in the UK of which around 91% are located in England and 6% in Scotland, according to the Association for Decentralised Energy (ADE). Heat networks are not suited to all buildings, but as many as 50% of buildings in the UK are in areas of suitable density for heat networks, says the ADE. It claims that the government estimates between 3 and 8 million dwellings, as well as a major share of commercial and public buildings, can be connected to heat networks at reasonable cost ( https://bit.ly/2BLTA34 ). There are essentially two types of heat networks – communal heating and district heating – both of which can employ heat pump technology. Communal heating is the supply of heat and hot water, typically from an energy centre to several customers within a single building. The energy centre might comprise a large boiler in the basement of a building or a heat pump on a roof or in a plant compound, with the heat and hot water distributed through the building via pipes. However, delivery of low carbon heat has resulted in a marked shift away from natural gas towards electrified heating systems. With the electricity grid now very much decarbonised, heat pumps have become a viable alternative to fossil-fuel powered systems. Another benefit of using heat pumps in commercial and high- end residential heat network installations is the potential to provide cooling as a by-product of the heating, the heat source being the cooling systems of the served properties. District heating involves a local energy centre that supplies heat and hot water to customers in more than one building. District heating networks can vary in size from a few hundred metres supplying just a few homes to several kilometres of pipe supplying heat and hot water to multiple buildings in a development. The potential exists for heat pumps to be integrated into heat networks in a variety of configurations, including: • Retrofitting a heat pump into an existing district heating scheme to provide a low carbon source of heat to the network. • Using a low temperature heat network in conjunction with distributed heat pumps in buildings, to increase the temperature at or near the point of use. • Linking buildings using a network which can be used as a heat source or heat sink for reversible heat pumps in each building, for high efficiency heating and cooling. THE PLACE OF HEAT PUMPS IN DISTRICT HEATING A landmark report – Heat Pumps in District Heating ( https://bit.ly/3CJ5us7 ) – published by the then Department of Energy and Climate Change in February 2016, recognises the value of using heat pumps in district heating to lower carbon emissions in place of central gas boilers or fossil fuel-based combined heat & power (CHP). The report explains that incorporating heat pumps into district heating schemes has the potential to offer large carbon dioxide (CO 2 ) savings relative to district heating based on either gas CHP for large schemes or gas boilers for small schemes. Assuming the current trajectory towards low carbon electricity generation, CO 2 savings versus gas burning schemes are in the range 48-84%. The carbon savings are found to be greatest where: • Heat pumps provide a larger fraction of the heating. • Heat pumps operate with a lower source-sink temperature difference resulting in better efficiency. • Network thermal losses are lower, especially for lower temperature distribution networks with building integrated heat pumps. Heat pumps bring potential additional benefits that may shift the economic balance in their favour compared to the alternatives. In particular, the ability to provide cooling as well as heating has been found to be a key driver for the use of heat pumps in heat networks. Moreover, a particular advantage of electrifying heating and cooling via heat pump usage is that there is an opportunity to take advantage of ‘demand response’ – when heating time is diverted from peak to off-peak hours, the price of heating falls and relieves the grid of stress.