Comparative life cycle assessment of district heating supply pathways: Insights from waste heat and CHP configurations

• Introduced a novel dual-assessment framework for LCA of DH supply systems. • Simultaneously assessed embodied and operational carbon in DH systems. • Compared waste heat and CHP options under fuel and efficiency uncertainties. • Identified biogas CHP as the lowest-carbon option with 72.9 % emission reduction. • Informed future DH policy and design through system-wide carbon analysis. Decarbonising heat is a critical challenge for achieving climate goals, as heating accounts for around 40 % of global energy demand and nearly 30 % of global greenhouse gas (GHG) emissions. District heating (DH) systems provide a scalable, low-carbon alternative to decentralised heating; however, their Life Cycle Assessment (LCA), particularly when integrating renewable supply options, remains underexplored in the literature, especially for emerging markets such as Ireland. This study introduces a novel integrated LCA framework that captures both embodied and operational carbon emissions of alternative DH supply configurations. The framework combines SimaPro for life cycle inventory with HOMER Pro for techno-economic modelling and includes sensitivity analysis of critical parameters. Three scenarios were assessed: a waste-heat-fed DH system, a natural gas combined heat and power (CHP) system, and a biogas CHP system. The results show that the waste heat-fed system exhibits the highest embodied emissions (402,000 kg CO 2 eq) compared with 256,000 kg CO 2 eq for the biogas CHP. In terms of operation, the biogas CHP system achieves up to a 72.9 % reduction in annual GHG emissions relative to natural gas CHP. Over a 20-year lifetime, the biogas CHP achieves the lowest overall life cycle carbon footprint per functional unit, compared with natural gas CHP. These findings highlight the value of integrating life cycle carbon assessment into DH system evaluation and provide practical insights for policy and infrastructure planning to accelerate the decarbonisation of heating.