HYBRID ENERGY CENTRES | HEAT PUMP SIZING FORMULA FOR SUCCESS: SIZING HEAT PUMPS IN HYBRID ENERGY CENTRES Reducing the size of heat pumps in hybrid energy centres can cut carbon and capital costs dramatically but what ratio of heat should they supply? Research by FairHeats Ellie Hiscock used hourly load modelling to come up with a rule of thumb for the optimal heat ratios for heat pumps and thermal storage with electric boilers T he UK is making strides towards decarbonisation of its electricity grid, and heat pumps are playing a crucial role in this transition. Most new heat networks are now shifting towards all-electric heat generation, with heat pumps replacing gas combined heat and power (CHP) as the lead heat generation source. However, there can be a significant increase in spatial requirements and capital expenditure when using heat pumps as the lead heatgeneration source for heat networks, compared with gas CHP and gas boiler solutions. To tackle this issue, I propose a hybrid approach that combines heat pump and thermal storage with electric boilers. Thermal storage increases operational flexibility of heat pumps and maximises the annual target heat fraction that can be provided by the heat pumps. My research, How hourly load modelling is revolutionising heat pump and thermal store sizing in hybrid energy centres, was presented at the CIBSE ASHRAE Technical Symposium 2023, at the University of Strathclyde, Glasgow, in April (www.cibse.org/symposium). It provides a rule of thumb for hybrid energy centres to support designers and developers early in the design stages, ensuring that heat Thermal storage system in a district heating energy centre pump size and thermal storage capacity are optimised to achieve the required target heat fraction contribution, which is the proportion of the total annual network consumption that is provided by the heat pumps. The heat pumps are sized to deliver the majority of the site-wide annual heat demand, with large thermal storage used to reduce the required heat pump size by storing heat during times of lower demand and using it during periods of higher demand. Electric boilers are sized to act as top up during periods of peak load demand. It is important to consider equipment sizing early on in the design stages, as such decisions could be constrained later by architectural layouts, floor plans and building elevations. This is where my research comes in. Modelling heating and hot water use In my research, an hourly load model was built, which aims to model the domestic hot water (DHW) and space heating usage that can be assumed for each hour across an entire year for any given development. The model takes into account several inputs to investigate the impact of equipment sizing on the heat pumps annual heat fraction contribution. These include: heat network heat losses; heat interface unit heat losses; DHW hourly profile; space heating hourly profile; and annual DHW and space heating loads. www.cibsejournal.com August 2023 35