Figure 2. Green energy-based

systems, hydrogen above, and district heating below.

Methodology This article aims to evaluate the energy intensity and GWP of a future energy system that utilizes either blue energy, decar- bonized natural gas, or renewable energy for fulfilling building heating demands. The analysis is based on examining the en- ergy supply chain, from primary energy input to the energy system to the end-user of heat. For the blue energy systems, the system boundary extends from the gas field development to the heat-consuming buildings, see Figure 1. In renewable energy systems, the system boundary extends from the point where the renewable power enters the power transmission grid to the heat-consuming buildings, see Figure 2. When estimating the overall supply system efficiency, the effi- ciency and fugitive emission of each step is estimated, based on a literature review. Results While several different thermal sources would generally supply DH, this analysis assumes that both heat supply systems are based on the same primary energy input. This simplification enables a one-to-one comparison of the primary energy de-

mands of DH and hydrogen-based heat supply systems. The below Sankey diagrams visualize the main results of the study, the primary energy demands, the energy efficiencies along the supply chain, and the value of matching the supplied energy quality with the demanded energy quality. Comparison of the Sankey diagrams for the blue scenarios, Figure 3 and Figure 4, show that the superiority of blue DH originates from the ability to capture waste heat from primary fuel conversions and by incorporating ambient heat, via heat pumps, into the heat supply. Utilizing the waste and ambient heat greatly reduces the primary energy demand compared to the blue hydrogen alternative. The lower primary energy de- mand further leads to significantly lower short- and long-term GWP potential compared to the blue hydrogen alternative, as shown in Table 1. In the green scenarios, Figure 5 and Figure 6, the ability of DH to utilize heat pumps becomes even more advantageous, lead- ing to significantly lower primary energy demand compared to the green hydrogen alternative.

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