Abstract
The heat decarbonisation challenge remains substantial, competing low carbon solutions such as hydrogen and heat pumps (HPs) and the entrenched position of gas combination boilers create inertia in many markets. Hybrid appliances which can directly replace gas boilers may provide a low disruption, low-cost pathway to net zero in gas-reliant markets. Emerging compact combination (CoCo) hybrid heating appliances which combine a gas combi boiler and a small HP unit in one appliance have been modelled for the English housing stock across a range of different scenarios. CoCo hybrids offer sizeable energy demand reduction of up to 60% compared to current gas boilers, also reducing peak electrical demand by 10 GW compared to air source heat pumps. The control strategy for switching between HP and gas boiler is key in determining the scale of demand reduction. Modelling sensitivity to the HP size within CoCo hybrids showed that a 50% reduction in energy demand compared to gas boilers could be achieved with a standard 2.5 kW HP. A lack of clarity in regulation and policy incentives for hybrids exists. To drive innovation and performance improvement, product regulation for hybrids needs to be improved to support decarbonisation of heat with this promising technology. Practical Application Convenient, low disruption heat decarbonisation technology is crucial to the speed of deployment necessary to achieve net zero. This article defines the size of HP necessary to achieve rapid low disruption impact and distinguishes the types of compact hybrid which can deliver the highest decarbonisation impact while minimising in house disruption and the electrical grid impact.
Highlights
Domestic energy demand accounts for 29%1 of the UK national total
Energy is used within the home primarily for space heating and gas boilers continue to dominate domestic heating in the UK making up the majority of the 22 million homes heated by fossil fuel boilers.[2]
The UK Government plans to eliminate fossil fuel gas connections from new buildings and the IEA is recommending that only hydrogen ready boilers are installed from 2025.6 Heat pumps play a central role in Government policy, aiming to increase the deployment of heat pumps (HPs) annually to 600,000 from 30,000 in 7 years.[7]
Summary
Domestic energy demand accounts for 29%1 of the UK national total. Energy is used within the home primarily for space heating and gas boilers continue to dominate domestic heating in the UK making up the majority of the 22 million homes heated by fossil fuel boilers.[2]. And disruptive aspects of HP installation can be averted with hybrid systems, such as the upgrading of radiators or the installation of a hot water tank This is seen as a ‘low regrets’ policy move due to the preservation of multiple decarbonisation options the future including, district heating, fully electric heating and hydrogen based heating pathways. Bivalent systems with active secondary heat sources (HPs, biomass burners rather than passive solar thermal) have cost and space implications due to the redundancy built in and the lack of integration The complexity of this type of bivalent boiler/HP system presents a challenge to occupants and heating professionals which can be exacerbated when incompatible equipment from multiple manufacturers is installed. This research endeavours to understand to what extent the modest size of the HP within a CoCo hybrid could deliver carbon savings of HP heating while mitigating the necessity for widescale grid reinforcement during a transition
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