Modelling case study of compact combination hybrids as low disruption decarbonised heat

Transitioning from predominantly natural gas domestic heating to low carbon heating is one of the major challenges of the UK’s net zero decarbonisation pathway. Compact wall-hung combination boilers are the dominant heating appliance and continue to be installed as a rate of over 1.5 million per year, compared to less than 50 k per year for Heat Pumps. The disparity persists despite repeated Government support in the form of the Renewable Heat Incentive and the Green Homes Grant. Compact hybrid appliances offer a technology solution similar to the current combination boiler in terms of size and performance, which could be attractive to consumers. However, there is currently little knowledge of the emissions savings that could be achieved in practice by compact hybrid appliances. This research systematically analyses real world high frequency boiler data to evaluate the potential of such appliances to make carbon savings while emulating combination boiler operation. By utilising high frequency diagnostic data from combination boilers, the disaggregated (hot water and heating) demand is mapped onto hybrid models to determine the energy and emission impact. Exploration of the relative power output of the HP and boiler components of the modelled hybrid appliances provides insight into the appropriate specification of compact hybrids which can deliver similar heat service to boilers while maximising emissions savings. The analysis shows that hybrid appliances with moderately sized HPs can significantly contribute to the decarbonisation of the homes considered in the study. Considerable disruption could be avoided in retrofit due to the physical size of the proposed heat pump and ability of the hybrid system to operate with the existing heat emitter network.