Heat pumps for space heating and domestic hot water production in residential buildings, an environmental comparison in a present and future scenario

The hydrogen vector stands as a potentially important tool to achieve the decarbonization of the energy sector. It represents an option to store the periodic excesses of energy generation from renewable electrical sources to be used as it is as a substitute for fossil fuels in some applications or reconverted into electricity when needed. In this context, hydrogen can significantly decarbonize the building sector as an alternative fuel for gas-driven devices. Along with hydrogen, the European strategic vision indicates the electrification of heat among the main energy transition pathways. The potential environmental benefits achievable from renewable hydrogen in thermally-driven appliances and the electrification of residential heat through electric heat pumps were evaluated and compared in this work. The novelty of the research consists of a consequential comparative life cycle assessment (16 impact categories) evaluation for three buildings (old, old retrofitted, and new) supplied by three different appliances (condensing boiler, gas absorption heat pump, and electric heat pump), never investigated before. The energy transition was evaluated for 2020 and 2030 scenarios, considering the impact of gaseous fuels (natural gas and European green hydrogen) and electricity based on the pathway of the European electricity grid. (27 European member states plus the United Kingdom). The results allowed to compare the environmental profile in deterministic and stochastic approaches and confirm if the increase of renewables reduces the impact in the operational phase of the appliances. The results demonstrate that despite the increased renewable share, the use phase remains the most significant for both temporal scenarios, contributing to 91% of the environmental profile. Despite the higher footprint in 2020 compared to the electric heat pump (198-200 vs. 170-196 gCO2eq/kWhth), the gas absorption heat pump offered a lower environmental profile than the others in all the scenarios analyzed.