1 Simulations of Material Flows in a District Heating System - Influence of Solar Heating and Flue Gas Condensing Ola Eriksson 1 , Johanna Olander 2 and Björn Frostell 1 1 Industrial Ecology - Royal Institute of Technology, Stockholm, Sweden 2 Cap Gemini, Stockholm, Sweden Abstract Stockholm Energi is the main supplier of district heating and electricity in the city of Stockholm. A systems analysis of introducing flue gas condensing and solar heating in the southern part of Stockholm was made. In this, annual flows of carbon, nitrogen, sulphur and phosphorus were studied. An Excel based simulation model was developed for calculations and presentation of results. A combination of flue gas condensing, solar heating and long-term heat storage would decrease the flow of the studied materials with 15 - 20 %. Material Flow Analysis proved to be an interesting possibility to study environmental pressure from energy systems. Key words: substance flow analysis, systems analysis, material flows, solar heating, flue gas condensing Introduction Much of current discussions on sustainable development focuses on a decreased material intensity in various products and processes (von Weizsäcker et al, 1997). Of particular importance in such a development is the dematerialisation of energy supply. This is since at the moment, the main material flow disturbances on a global scale may be attributed to the global energy supply system. Stockholm Energi is the main supplier of district heating and electricity in the city of Stockholm. In district heating, a few big centralised plants are used to supply surrounding city areas with hot water for space heating of apartments, offices and industrial facilities and for the production of hot tap water. The district hot water circulates in large, insulated, buried pipes. In each building, a heat exchanger is used to transfer the district heat to the buildings local net for further distribution of heat and hot tap water. Beginning a number of years ago, Stockholm Energi has continuously striven to decrease the environmental impact of services supplied. Fossil fuels have gradually been replaced by biofuels, such as tall oil pitch. Stockholm Energi is also responsible for energy and district cooling supply in the Hammarby Sjöstad project, one of the largest ecologically oriented city development projects in the world. Here, the goal is to develop a city area with twice as good an environmental performance as that achieved currently in Stockholm (Stockholm 1995). An important aim for Stockholm Energi is to reduce emissions of fossil carbon. This may be achieved either by increasing the efficiency in the current facilities or introducing new energy supply systems with better material turn over characteristics. As a part of the work to develop an environmentally benign energy supply, a systems analysis of introducing flue gas condensing and solar heating in the Southern Net of Stockholm was investigated. Two main reasons to investigate a combination of flue gas condensing and solar heating were: