both improvements across the two reference systems. With a wider system boundary, the higher-order benefits may justify solutions that seem unjustifiable under a narrow boundary, such as an improved heat exchanger in heat interface units of heat pump-supplied systems. Comparing Table 3 and Table 4. Impact analysis for a wide system boundary, including all elements of the thermal supply system. reveals that for sources sensitive to operating temperatures, such as heat pumps, a narrow system boundary can significantly underestimate the benefits of efficiency improvements, including cost, emissions, and primary energy savings. For high-temperature sources, such as fuel boilers, a narrow boundary may suffice for supply temperature reductions. However, when solutions lower the return temperature, the boundary should at least include the heat source to capture potential efficiency gains from flue gas condensation.
Table 2 illustrates the approximate effects of changes in the system operating temperatures on the heat generation plants.
Expected Impact of Improvement Measures Traditionally, the impact of these solutions is evaluated only within the distribution network (double-outlined in Figure 1), as lowering operating temperatures in high-temperature, fossil-based systems primarily affects distribution losses. Table 3 illustrates the potential impact of this narrow system boundary on both temperature optimization and return- temperature reduction through an improved heat exchanger. Table 3 suggests that the cost savings potential is limited, making it challenging to justify investment-heavy improvements, such as upgrading heat exchangers in energy transfer stations. In contrast, system solutions, like software- based temperature optimization, appear more attractive. Extending the system boundary to the full thermal supply system shown in Figure 1 reveals higher-order benefits, which include impacts from upstream and downstream efficiency improvements, as well as changes in the fuel mix. Table 4. Impact analysis for a wide system boundary, including all elements of the thermal supply system. shows results for
System Efficiency First: Framework for Future Proofing District Heating
DH is a cornerstone of the clean energy transition, particularly for the sustainable utilization of low-temperature energy sources. However, with the transition toward low-temperature
Cost savings [EUR/year]
Reference system efficiency
System efficiency after improvements
Heat savings [MWh/year]
CO2 eq reduction [ton CO2 eq /year]
Base load source
Either supply or return temperature is reduced by 5°C
Biomass boiler
90%
90.5%
715
32.7
25,000
Heat pump
90%
90.5%
715
162.7
20,700
Table 3. Impact analysis for a narrow system boundary, only including the distribution network.
Cost savings [EUR/year]
Reference system efficiency
System efficiency after improvements
Primary energy savings [MWh/year]
CO2 eq reduction [ton CO2 eq /year]
Base load source
Distribution system temperature optimization – 5°C reduction in supply temperature
Biomass: 670 nGas: 710
Biomass boiler
83.6%
84.2%
450
29,200
Green power: 0 nGas: 9,380
CO2 heat pump
189.7%
216.1%
5,770
368,500
Improved heat exchanger at energy transfer stations – 5°C reduction in return temperature
Biomass: 1,430 nGas: 960
Biomass boiler
83.6%
84.9%
620
67,400
Green power: 0 nGas: 12,930
CO2 heat pump
189.7%
229.4%
7,950
517,700
Table 4. Impact analysis for a wide system boundary, including all elements of the thermal supply system.
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