Economic and environmental assessment of hybrid heat pumps: a cross-country analysis

Decarbonizing the residential heating sector requires flexible and efficient alternatives to conventional systems. Hybrid heat pumps (HHPs), combining an air-to-water electric heat pump and a natural gas condensing boiler operating in an alternative manner, represent a promising solution to improve the sustainability of the residential heating sector. However, their integration into the building stock of different countries, along with the impact of component sizing and control strategies, remains underexplored. In this study, the thermal behavior of benchmark residential buildings located in Italy and Spain is dynamically simulated, considering both heating and domestic hot water (DHW) loads. Various generator sizes and control strategies are tested to evaluate annual operational costs and carbon emissions. Results show that, under ideal sizing and optimal control conditions, HHPs can lead to substantial economic and environmental benefits compared to the use of a condensing boiler alone. In Spain, cost and emission savings reach up to 50% and 60% respectively, whereas in Italy the maximum reductions are limited to 20% and 30%, due to differences in electricity generation mix and energy carrier prices. The adoption of conventional rule-based control strategies reduces these advantages, and in Italy, economic savings are not always guaranteed. Furthermore, the DHW demand has been found as an important driver of the overall system performance. These findings highlight the importance of proper design and sizing of hybrid systems, suggesting context-specific strategies to optimize their deployment in residential buildings.