Open Access

Decarbonizing the EU’s district heating is crucial for meeting climate goals and securing a sustainable energy future. Currently, district heating suffers from inefficiency, high operating temperatures, significant distribution losses, and reliance on fossil fuels. Literature highlights strategies for reducing emissions, including integrating low-carbon heat sources, lowering supply temperatures, and employing efficient technologies like heat pumps and combined heat and power (CHP). However, the individual effectiveness of these strategies in reducing emissions within existing networks remains unassessed. This study addresses the gap by applying a comprehensive model that evaluates energy and emissions across the district heating supply chain, coupled with a derivative-based sensitivity analysis. We apply this methodology to the national-level district heating systems of Sweden, France, Germany, and Poland. Results indicate that the impact of decarbonization strategies on district heating emissions varies significantly by the system’s characteristics, i.e., the energy mix in power and district heating supply and the presence of CHP plants. Primarily, incorporating more low-carbon heat sources emerges as the most effective method for emission reduction across nearly all examined countries. A 1 % increase in the share of low-carbon heat sources can potentially cut emissions by 0.8–1.3 kg CO2e per GJ of heat. In countries like Sweden and France, where the power generation already relies heavily on low-carbon resources, technologies which convert electricity to heat—such as heat pumps and electric boilers—rank as the second most effective approach. In contrast, for countries like Germany and Poland, with their moderate to low use of low-carbon power, reducing distribution losses and decreasing heat demand prove more effective, with emission reductions ranging between 0.8-1.3 and 0.7–1.2 kg CO2e per GJ in these countries, respectively. Additionally, cutting down power generation in fossil fuel-based CHP plants significantly reduces emissions in these regions. While green hydrogen and carbon capture and storage (CCS) also contribute to emission reductions, a 1 % increase in green hydrogen’s share might decrease emissions by just 0.3–0.5 kg CO2e per GJ of heat, highlighting their lower effectiveness compared to the aforementioned strategies. These insights hold value for both district heating operators and for technology suppliers seeking decarbonization pathways. This is also true for policy- makers focused on climate change mitigation, guiding the distribution of subsidies and R&D investments.

This study presents a method and graphical representation for optimizing the operational strategy of urban energy systems to simultaneously meet electricity and heat demands. Building on Part 1, "Designing a Fully Renewable Urban Energy System: The Meaning of Sector Coupling and Hydrogen," this paper addresses the previously open question of effectively operating a complex structure of multiple energy converters. By introducing a two-dimensional merit order principle, the study systematically prioritizes the use of energy converters based on their efficiency and role in balancing heat, electricity, and hydrogen demands. Visualized through a graphical representation, this approach offers an intuitive understanding of how different energy converters interact to meet demand states, elucidating why specific converters are employed under varying conditions. By providing valuable insights into cross-sectoral energy integration, this methodology serves as both a planning tool and educational resource. It highlights the optimal deployment of specific technologies, with applicability extending to other coupled energy systems, such as heating and cooling systems in diverse contexts.

As decarbonization accelerates across policy, markets, and supply chains, small and medium-sized manufacturers face growing demands to quantify organizational climate impacts and to target the main sources of emissions. This study defines the foundational elements of a streamlined organizational assessment for manufacturing SMEs that is practical, repeatable, and aligned with real data constraints. Building on ISO 14072, ISO 14040, and ISO 14044, and drawing on UNEP O-LCA and ILCD guidance, it reviews relevant standards and conducts a sector scan of six public reports in plastics components and industrial machinery to identify where methodological choices most influence screening outcomes. Two screening designs are proposed that fix goal and scope, and specify an inventory strategy using hybrid data collection, tiered data quality, simple cut-off rules, and clear electricity accounting conventions. The designs align LCA guidelines with sector patterns to enable consistent scoping, efficient data requests, and transparent assumptions. The screening designs are meant to guide screening LCAs that retain broad climate-relevant coverage but rely on streamlined data for key emission sources. The result is an initial technical basis for accessible organizational assessments tailored to German manufacturing SMEs, intended to lower technical barriers, support credible prioritization of action, and improve integration with supply chain sustainability practices.