Mapping of low temperature heat sources in Denmark

Low temperature heat sources are available in many applications, ranging from waste heat from industrial processes and buildings to geothermal and solar heat sources. Technical advancements, such as heat pumps with novel cycle design and multi-component working fluids, make the utilisation of many of those heat sources feasible. In this work a mapping of those heat sources is performed to gain an overview of the potential amount of waste heat and natural heat sources in Denmark. The energy potentials are mapped together with the temperature ranges at which the heat is available and the exergy content of the heat. The mapping is based on data and literature primarily published by Statistics Denmark and the Danish Energy Agency, as well as interviews with specialists and engineering estimates. The results indicate that up to 13 % of the energy input to the analysed sectors is available as waste heat. The total accessible waste heat potential is found to be approximately 266 PJ per year with 58 % of it below 100 °C. In the natural heat category, temperatures below 20 °C originate from ambient air, sea water and shallow geothermal energy, and temperatures up to 100 °C are found for solar and deep geothermal energy. The theoretical solar thermal potential alone would be above 500 PJ per year. For the development of advanced thermodynamic cycles for the integration of heat sources in the Danish energy system, several areas of interest are determined. In the maritime transport sector a high potential is found in exhaust gases, where also high temperatures are present. Also the industry sector has a large waste heat recovery potential from refrigeration and cooling processes, however at much lower temperatures.