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HEAT NETWORKS | THERMAL STORES SIZING UP THE BENEFITS: OVERSIZED THERMAL STORAGE IN HEAT NETWORKS Oversized thermal stores in heat networks could cut electric boiler capacity by up to 30%, says FairHeats Jake Adamson, who looks at data from existing heat networks and the potential for thermal stores T he UK has set ambitious but necessary carbon-reduction targets, and heat networks are one solution for achieving these goals. These networks are transitioning from gas-fired to electrically powered heat sources, which means using heat pumps and electric boilers as primary sources of heat in a hybrid generation arrangement. But how do we make sure these networks deliver low carbon heat efficiently? My latest research, presented at the FairHeat Annual conference and selected to feature in the CIBSE Technical Symposium 2023, provides valuable insight into this very question. A frequent topic in design meetings with clients was the large anticipated electrical capacities required on site, and the developer expenditure on upgrades to the local grid to accommodate this. I saw this as an area to explore and see if we could start to cut these costs through reductions to the total electric capacity, while maintaining network performances. The FairHeat Graduate Scheme gave me the resources and support I needed to conduct this research, which not only enhances FairHeats knowledge base and practices, but is also shared with the wider industry for everyones benefit. In the past, we have ventured into predictive A thermal storage system in a district heating energy centre hourly models to select heat pump and thermal storage sizes. However, the purpose of the research was to use operational heat network data to assess how the size of thermal storage would have impacted the required boiler capacity during the peak months: typically November to March. The findings showed that by increasing and oversizing the thermal storage volume, it is possible that marginal reductions in electric boiler capacity, in the region of 15-30%, could start to be considered. This could result in capital cost savings for developers but it also poses a risk that must be mitigated. To explain, heat pumps have relatively high capital costs, so its optimal to maximise the thermal storage volume to minimise the required heat pump size for the majority of heat networks. This allows the heat pump to deliver a target annual heat fraction, with electric boilers used to meet peak demand. Previously, it was acceptable to run the heat pumps to target 80% of the annual heat fraction when topped up by gas boilers. With the large running costs of electric boilers, however, supplying 20% of the heat fraction with these boilers is not achievable while maintaining a fair cost of heat. These days, we typically have to target a 95% heat fraction from the heat pump when topped up by electric boilers to maintain a fair cost to the end user. The data from existing heat networks on residential schemes has provided a greater understanding of the heat-demand profile of the www.cibsejournal.com November 2023 51