Consulting Engineer, FairHeat


Significant progress has been made in the industry with specification of heat generation equipment to meet the updated Building Regulations and GLA requirements and carbon reduction targets. However, the Future Homes Standard currently requires gas to be phased out of all developments from 2025 onwards, meaning that consideration is required as to the optimal strategy to supply heat to heat networks using only electricity.

This paper details the findings of a lifecycle assessment investigating the impact of various heat pump led energy strategies on system capital and operating costs. Six different energy strategies were compared for a typical 500 dwelling scheme during this research, which are: ASHP & gas boiler top up, GSHP & gas boiler top up, ASHP & electric boiler top up, GSHP & electric boiler top up, ASHP only, GSHP only.

The key conclusions of this research are from a lifecycle perspective, the optimal heat fraction is c.80% for gas boiler hybrid systems. However, all high heat fraction gas hybrid systems are comparable, so there is a minimal lifecycle impact to maximising the heat fraction whilst retaining the hybrid strategy to maximise carbon reduction. The lifecycle cost of electric boiler systems decreases for all hybrid systems up to a c.98% heat fraction. There is not a case for 100% heat pump solutions when considering both upfront and lifecycle costs.

Furthermore, the research showed that the increase in CAPEX due to an increase in heat fraction is compensated by a reduction in carbon offset payments (at £95/ tonne CO2 for 30-years) up to a 98% heat fraction for an ASHP gas hybrid system, and is cost beneficial or neutral up to a 95% heat fraction for an ASHP electric hybrid system. For GSHP hybrid system, the increase in CAPEX is offset up to heat fractions of c.80% with gas boilers and c.60% with electric boilers. The offset payment is therefore a powerful regulatory tool that should be used by local authorities to accelerate decarbonisation.