Distribution network operates at 80°C supply and 40°C return. Reference operation assumes a 10% relative network heat loss (12,700 MWh/year). Heat sources: Base load covers 60% of peak capacity, corresponding to 96% of annual demand; peak load natural gas boilers cover the remaining 40% of peak capacity, corresponding to 4% of annual demand. The total heat generation, including final heat consumption, building and distribution losses, is 127,000 MWh/year. Figure 2 shows the system duration curve. Table 1. Efficiencies, see [2], and the cost of primary energy (PE) sources. shows assumptions related to the primary energy (PE) supply. Considered Improvement Measures and Their Impact on Heat Generation To demonstrate the importance of wide system boundaries when evaluating the impact of efficiency improvements, two complementary solutions are considered:
Figure 2: Duration curve of the system heat demand.
Reference Systems To illustrate the value of a holistic approach, two reference systems are considered, identical except for the baseload heat source, which is either based on a biomass boiler or a CO2 heat pump. These two systems can be considered as two future alternatives for an existing fossil-based system. Alternatively, it can be viewed as an existing biomass-based system, with a planned future replacement by a CO2 heat pump. The holistic assessment framework empowers decision-makers to assess long-term investment impacts and plan accordingly. Key system data: Annual final heating demand: 100,000 MWh (80,000 MWh for space heating, 20,000 MWh for domestic hot water), plus 14,300 MWh losses in energy transfer stations and building heat distribution.
a) Temperature optimization of the distribution network, achieving a 5 °C reduction in supply temperature.
b) Heat exchanger replacement in energy transfer stations (substations), achieving a 5 °C reduction in return temperature.
Both solutions have a proven track record, yet have substantial implementation potential remaining.
PE harvesting, mining and processing efficiency
PE conversion efficiency
Distribution efficiency
Fuel source
Total efficiency Fuel cost [EUR/MWh]
Grid electricity
N/A
N/A
98%
72.2%
100
- Renewable electricity
100%
N/A
N/A
100%
N/A
- Gas-based electricity
88.6% (nGas)
50%
N/A
44.3%
N/A
Biomass
95%
N/A
98%
93.1%
40
Natural gas
90%
N/A
98.5%
88.6%
41
Table 1. Efficiencies, see [2], and the cost of primary energy (PE) sources.
Impact on heat generation
Heat source
Reference efficiency [3]
T supply / Efficiency
T return / Efficiency 1°C ↓ / 3% ↑ 1°C ↓ / 0.2% ↑ 1°C ↓ / 0.16% ↑
1°C ↓ / 2% ↑ 1°C ↓ / 0% 1°C ↓ / 0%
CO2 heat pump [4]
350%
Biomass boiler
115%
Natural gas boiler
103%
Table 2. Expected impact from reduced operating temperatures on the heat generation efficiency.
16 HOTCOOL SPECIAL COLLECTION edition 2, 2025
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