Abstract. The potentials of energy conservation and emission mitigation are investigated by thermoeconomic systems analysis for a district heating system of 100 well-insulated housing units. The technologies considered are solar collectors, heat exchangers, the seasonal storage of solar heat, (gas-fired) condensing boilers, heat pumps, and the cogeneration of heat and electric- ity. Appropriate combinations of these technologies yield (non-renewable primary) energy savings between 15% and 35% associated with cost increases between 20% and 140% compared to a reference case with individual condensing boilers and electricity taken from the public grid. 1 Introduction Thermal physics considerations are crucial in the design of strategies for the rational use of energy and emission mitigation. The key to improving the energy efficiency of industrial plants has been the optimisation of exergy consumption with the help of heat- exchanger networks, heat pumps, and the cogeneration of heat and electricity. In order to find out the optimum combination of these technologies that minimises energy inputs and costs to satisfy a given demand for heat and electricity the system-analytical methods of thermoeconomics have been developed (Kenney 1984). These methods have been extended to national and regional energy systems; the first ones have been modelled in a highly aggregate way (Groscurth 1990) whereas for the latter ones it has been possible to take into account the individual energy supply processes and the fluctuations of heat and electricity demand as well as ambient temperature and insolation during one repre- sentative year (Groscurth and Ku«mmel 1993; Bruckner et al 1997). Furthermore, the collection and storage of solar thermal heat has been included in the dynamic energy, emission and cost optimisation model ‘deeco’ (Bruckner 1997).This model has been used to support the design of a pilot housing project within the research cooperation SOLEG (Solar unterstu« tzte Energieversorgung von Geba«uden, solar supported energy supply for buildings) initiated by the Zentrum fu«r Angewandte Energieforschung ZAE Bayern and the Bayerische Forschungsstiftung. Here we report some results obtained by the applica- tion of deeco to solar-supported district heating systems with seasonal heat storage and integrated (gas-fired) condensing boilers, heat pumps, and cogeneration. Details concerning the technical parameters and costs of these technologies as well as the system-analytical methodology are presented elsewhere (Lindenberger et al 2000). Heat, electricity, Sun, and fossil fuels: dynamic energy, emission, and cost optimisation High Temperatures ^ High Pressures, 2001, volume 33, pages 463 ^ 468 15 ECTP Proceedings pages 1031 ^ 1036 Dietmar Lindenberger Institute of Energy Economics, University of Cologne, Albertus-Magnus-Platz, D-50923 Cologne, Germany; fax: +49 221 44 65 37; email: Lindenberger@wiso.uni.koeln.de Thomas Bruckner Institute for Energy Engineering, Technical University of Berlin, Marchstr.18, D-10587 Berlin, Germany Helmuth M Groscurth Hamburgische Electricita« ts-Werke AG (HEW), Uº berseering 12, D-22297 Hamburg, Germany Reiner Ku«mmel Institut fu« rTheoretische Physik der Universita« t Wu« rzburg, Am Hubland, D-97074 Wu« rzburg, Germany Presented at the 15th European Conference on Thermophysical Properties, Wu« rzburg, Germany, 5 ^ 9 September 1999 DOI:10.1068/htwu601