Assessing long-term sustainability of district heating systems
Conference contribution, 2012
Biomass has become the main fuel for district heating (DH) systems in Sweden, and the substitution of biomass for oil during the last decades has led to considerably reduced CO2 emissions within the DH systems. Today, biomass is used both in heat- only boilers and, increasingly, in combined heat-and-power plants. District heating contributes also to increased sustainability through the utilization of industrial waste heat, which substitutes for primary energy use.
With increasing pressure on constrained biomass resources and due to the geographical distribution of waste-heat sources, the municipal DH systems need to look for new solutions in order to further reduce their dependency on primary energy sources and enhance their sustainability. An integration of local systems into a regional heat system would allow for utilization of an increasing amount of waste heat, to capture scale effects of biomass combined heat and power plants and also to compensate for load profile differences between the local systems. DH systems are in addition being increasingly integrated with the power system and also with biorefineries through the production of bio transport fuels. Thus, the role of DH systems is becoming increasingly complex. This calls for new tools and methods to assess the sustainability of various possible future options and developments.
The aim of the study is to assess the long-term sustainability of different DH developments with a focus on possibilities for integration of local DH systems into a regional system. In order to assess the sustainability in a long-term perspective of future DH options, we combine methods such as energy systems modeling and life cycle assessment in a procedural framework called life cycle sustainability assessment. The energy systems model applied is an optimizing bottom-up model. The study concerns the Vastra Gotaland region of Sweden and our model represents all the municipal DH systems at a detailed level. This presentation will mainly focus on the methodological aspects of the work: on how the different methods can be integrated and applied in a sustainability assessment of future district heating.