Technical and economic assessment of a hybrid heat pump system as an energy retrofit measure in a residential building
Mohammad Saffari, David Keogh, Mattia De Rosa, Donal P. Finn
Energy and Buildings
School of Mechanical and Manufacturing Engineering

Air to water electric heat pumps are one clean energy contribution to mitigating climate change. Nevertheless, they may not necessarily be the only solution for all residential building stock. Extensive fabric refurbishment may make installation impracticable. Alternatively, where electric heat pumps may not be advisable where low ambient temperatures prevail and/or high water delivery temperatures must be utilised. For such instances, hybrid (gas and electric) heat pumps offer an alternative option by facilitating fuel source switching between electricity and gas, when ambient temperatures are low or high water supply temperatures are required.


In the current study, the efficacy of an air-to-water electric heat pump and hybrid heat pump are examined for different building retrofit scenarios for a residential dwelling located in Ireland. This is achieved by means of a sensitivity study of a validated building simulation model, incorporating both heat pump systems, subject to different building retrofit scenarios. Finally, the deployment of either an electric heat pump or hybrid heat pump for deep building fabric retrofit achieves approximately half of the heating system capital cost return within 20 years.

Improving the energy performance of the building sector has been well established as a key energy policy goal of the European Union (EU), given that the EU has committed to developing a sustainable, secure and carbon-free overall energy scenario by 2050. Given the building sector accounts for about 40% of primary energy consumption and 36% of associated greenhouse gas emissions in Europe, it plays a paramount role towards achieving a carbon-neutral and competitive economy. Currently, about 35% of EU buildings are over 50 years old, 75% of which do not meet the national energy performance targets according to the EU Directive 2018/844 on the energy performance of buildings.