Are district heating systems and renewable energy sources always an environmental win-win solution? A life cycle assessment case study in Tuscany, Italy

Space heating and cooling pose fundamental challenges to the achievement of EU decarbonization targets. A comprehensive review of the recent literature acknowledged that district energy systems contribute substantially to the sustainability of energy in the building sector by improving the efficiency and integration of low energy sources. However, a holistic evaluation of the environmental performance of such systems is advisable during the planning and design stage. In this study, we use life cycle assessment to assess the potential contribution and environmental sustainability of renewable heating and cooling alternatives. The unit of analysis is a residential neighbourhood of 1000 inhabitants (equivalent to 250 apartments), located in Tuscany, Italy, served by a district network that provides heating, cooling and sanitary hot water. A geothermal heat pump and a biomass system are compared to two systems based on natural gas as a fossil fuel: a centrally produced heating and cooling system and a more conventional system with single apartment boilers and air-air heat pumps for cooling. The cradle-to-grave analysis shows significant global GHG emission savings of about 35% for the biomass system and about 20% for the GHP system compared with the centralised benchmark system, increasing to 46% and 34%, respectively, with respect to the conventional standalone appliances system. However, other environmental impact categories show different levels of performance depending on the scenario, and in some cases their impact is even greater than that of the benchmarking scenarios. The contributions from each life cycle stage - assembly, operation and end of life - suggest that an eco-design approach could improve the global performances of each scenario. Recommendations for local planning authorities are drawn accordingly.