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Construction of new low-energy buildings (LEB) areas is attracting attention as a climate mitigation measure. Heat can be supplied to buildings in these areas through individual solutions, through a small, on-site heat network, or through a heat connection to a close-by district-heating (DH) system. The choice between these options affects the energy supply systems and their carbon emissions far beyond the LEB area. We compare the long-term systems impacts of the three heat-supply options through dynamic modelling of the energy systems. The study draws on data collected from a real LEB area in Sweden and addresses scale-dependent impacts on district heating systems. The results show that, generally, the individual and on-site options increase biomass and electricity use, respectively. This, in turn, increases carbon emissions in a broader systems perspective. The systems impacts of the large heat network option depend on the scale and supply-technologies of the DH system close to the LEB area.

Use of low-temperature heat sources in district heating (DH) systems is gaining attention as a climate mitigation measure. Urban excess heat (UEH) from data centres, metro stations, sewage systems and service sector buildings’ cooling system belongs to these sources. The use of UEH affects energy supply systems and system costs. We analyse the long-term system impacts of utilizing the four UEH sources through dynamic modelling of the energy systems. The study draws on data from real cases in four cities and addresses local conditions. The results show that UEH utilization can contribute to increased competitiveness of DH compared to individual heating. The system benefits are larger if UEH replaces boilers in DH system and/or in buildings.