Life cycle assessment of heat pump-based hydronic systems for multi-apartment buildings
Centralized heat pump (HP) systems are increasingly recognized as a sustainable solution for providing space heating (SH) and domestic hot water (DHW) in multi-apartment buildings. While previous life cycle assessment (LCA) studies highlight the environmental advantages of HP-based systems over conventional technologies, the influence of different hydronic distribution configurations has not yet been systematically investigated. This study conducts a comprehensive LCA of multiple centralized hydronic system variants for a large multi-apartment building with 52 apartments, integrating both embodied and operational impacts. Four configurations are analyzed: (1) a 2+2-pipe system with decentralized fresh water stations (FWS), (2) a 4-pipe circulation system, (3) a 2-pipe system with heat transfer stations (HTS) and (4) a 2-pipe system with decentralized electric boilers. All systems are designed and dimensioned according to conventional engineering rules, with component sizing based on SH loads and DHW profiles. The results indicate that the '2+2-pipe FWS' and '2-pipe HTS' variants exhibit the lowest global warming potential (GWP) over the entire life cycle. The '2-pipe E-Boiler' variant performs the worst of all options, causing at least 30 % higher emissions, even in the optimistic 2040 electricity mix scenario. A key finding is that operating energy has a significant impact on GWP. Under the conditions of the current Austrian electricity mix, the GWP of operation exceeds that of the manufacturing, construction, and disposal phases after around three years, with a magnitude that can be up to nineteen times greater over the entire life cycle. Overall, the findings emphasize the importance of low-temperature, efficiently dimensioned hydronic systems and highperformance building envelopes. Passive measures that reduce heating demand remain the most effective lever for minimizing life cycle emissions.