Significant contribution by geothermal energy and seasonal storages Currently, there are efforts to exploit deep geothermal resources in the Vienna Basin 22 . If successful, the renewable heat supply in Vienna’s DH network will be increased substantially. Since geothermal energy constitutes a base load supply and thus is in competition with the existing waste incineration plants, Wien Energie is investigating different options for seasonal storages. These include pit storages 23 as well as aquifer thermal energy storages (ATES), the use of groundwater-bearing geological formation in the deep underground 24 . A key enabler: decreasing the DH network temperatures Many Austrian DH networks are operating with high supply temperatures, ranging from 90 °C up to 150 °C (supply) and from 50 to 70 °C (return) 25 . These high temperatures are key barriers for the integration of alternative heat sources; however, technical, economical and legal barriers hamper the necessary investments for their reduction. A recent study has shown possible business models encouraging a substantial temperature reduction 26 . In this context, the assessment of the socio-economic benefits of reduced network temperatures is of major importance. An analysis of the Austrian DH sector showed savings of 0.42 €/(MWh·°C) resulting in absolute terms to several million Euros per °C and year, when the system temperature in all existing DH networks are reduced 27 . For systems with high share of waste heat, geothermal energy and seasonal storages, this number can be expected to be even higher 28 .
Figure 4: The ‘vicious circle’ of high system temperatures, b) the added value of low system temperatures
For buildings outside the DH network Buildings not connected to the large-scale DH network in Vienna are mainly supplied by gas boilers. Some innovative approaches for their replacement are given in 29 . An interesting option for larger refurbishment projects has been demonstrated in the project “Smart Block Geblergasse”. Here, a low-temperature DHC network has been implemented in a block of old buildings 30 . The project AnergieUrban builds upon this experience and investigated different heat supply options for existing buildings 31 . Since heat sources in urban areas are sometimes limited, options for harvesting solar excess heat from building surfaces, sidewalks, streets and squares are also investigated in research projects 32 .
Figure 5: Vision of the Heat-Harvest approach for harvesting solar excess heat and re-using it in winter 32
Made with FlippingBook Digital Publishing Software