by Linda Bertelsen

One of the main climate goals in Austria is to reach carbon neutrality by 2040. The renewable share in district heating (DH) is currently at 48.4%, of which the vast majority is biomass. This large share of biomass is mainly due to more than 2,400 small biomass-based rural DH networks. Apart from these, some larger DH networks exist in all major urban areas, i.e., Vienna, Graz, Linz, Salzburg, and Klagenfurt, mainly based on combined heat and power plants (CHP) using natural gas.

By Ralf-Roman Schmidt, Edith Haslinger, Roman Geyer, Benedikt Leitner, Dragisa Pantelic

One of the main climate goals in Austria is to reach carbon neutrality by 2040[1]. The renewable share in district heating (DH) is currently at 48.4 %, of which the vast majority is biomass[2]. This large share of biomass is mainly due to more than 2,400 small biomass-based rural DH networks[3]. Apart from these, some larger DH networks exist in all major urban areas, i.e., Vienna, Graz, Linz, Salzburg, and Klagenfurt, mainly based on combined heat and power plants (CHP) using natural gas.

The decarbonization roadmap of the Austrian DHC association

In 2020, the Austrian Association of Gas- and District Heating Supply Companies published a scenario for decarbonizing the Austrian DH sector[4]. Here, an increase in DH demand by around 30 % to almost 26 TWh is predicted, accounting for approx—30% of total heat consumption. On the supply side, besides the continuous use of waste heat and waste incineration, the most significant increase is due to geothermal energy. However, the overall largest heat supplier in 2050 will be renewable fuels, reaching a share of 59 %.

[1] https://www.bundeskanzleramt.gv.at/bundeskanzleramt/die-bundesregierung/regierungsdokumente.html
[2] https://www.bmk.gv.at/dam/jcr:f0bdbaa4-59f2-4bde-9af9-e139f9568769/Energie_in_OE_2020_ua.pdf.
[3] https://www.biomasseverband.at/wp-content/uploads/Bioenergie-Atlas-Oesterreich-2019.pdf
[4] https://www.forum-gww.at/pdf/2020_02.pdf

Figure 1 Decarbonization scenario for Austrian DHC networks (adapted and translated from )
Figure 1 Decarbonization scenario for Austrian DHC networks

Sustainability of biomass and the competition for renewable fuels

Although there are rich biomass resources in Austria, their utilization in general and more specific for heating purposes is increasingly questioned. In a recent statement, 500 scientists addressed heads of governments: “Trees are more valuable alive than dead for climate and biodiversity. To meet future net zero emission goals, your governments should work to preserve and restore forests and not to burn them[5]. Furthermore, studies on the decarbonization of the Austrian industry sector show a large demand for renewable fuels[6]. Following this trend, cities like Helsinki aim to decarbonize their heat supply while using as little biomass as possible[7].

[5] https://plattform-wald-klima.de/wp-content/uploads/2021/02/Scientist-Letter-to-Biden-von-der-Leyen-Michel-Suga-Moon-Re.-Forest-Biomass-February-11-2021.pdf
[6] https://www.mdpi.com/2076-3417/11/4/1819
[7] https://energychallenge.hel.fi/

Figure 2 District heating in Vienna, development by 2022

Best practice Vienna

With about 1.7 million inhabitants, Vienna is the largest city in Austria. More than 30 % of its buildings are supplied with DH. Its supply mix is dominated by gas CHP (52 %), waste incineration (21 %), and waste heat (18 %), while boilers, ambient heat, and biomass account for the remaining 9 %[8]. A study on the decarbonization of Vienna’s energy system[9] showed that the most important measures related to DH are integrating profound geothermal energy and large-scale heat pumps. Renewable fuels are expected only to cover peak loads on cold winter days. For a coordinated decarbonization effort, an energy planning concept considering urban and spatial planning has been implemented[10]. Here, a focus is put on using digital information models[11].

The most significant heat pump in Central Europe

Early on, Wien Energie invested in large-scale power-to-heat projects, e.g., two electrode boilers with a capacity of 10 MW each were installed in 2017[12]. Further on, since 2019, the largest heat pump in central Europe has been operating in Vienna, supplying about 25,000 households with heat. Cooling water from power plants in Simmering is used as a heat source. The HP has a thermal output from 27.2 to approximately 40 MW and a temperature lift from 6 to 95 degrees Celsius[13]. A recent project is related to utilizing waste heat from cooling processes in the large office buildings of UNO City[14]. Options like flue gas condensation from waste incineration are being investigated[15].

Waste heat in the focus

As one of the most essential sources for heat pumps, waste heat is the focus of investigations in Vienna. In 2017, the city’s energy planning department published a map of waste heat potentials in Vienna[16] based on a methodology described in a Blue Globe Report[17]. This effort is continued in the project Spatial Energy Planning[18].

[8] http://jahrbuch.wienenergie.at/de/2019/Amoiu7jm/geschaeftsverlauf-finanzielle-und-nichtfinanzielle/?page=1
[9] https://positionen.wienenergie.at/beitraege/decarb-studie/
[10] https://www.wien.gv.at/stadtentwicklung/strategien/step/step2025/fachkonzepte/energieraumplanung/index.html
[11] https://www.ait.ac.at/themen/digital-resilient-cities/projects/dim4energy/
[12] https://www.wienenergie.at/blog/wie-funktioniert-wiens-groesster-wasserkocher/
[13] https://www.wienenergie.at/blog/staerkste-grosswaermepumpe-mitteleuropas-pumpt-in-wien/
[14] https://www.wienenergie.at/pressrelease/hanke-strebl-uno-city-klimaanlagen-heizen-wien-ein/
[15] https://greenenergylab.at/projects/thermaflex/
[16] https://www.wien.gv.at/stadtentwicklung/energie/themenstadtplan/
[17] https://www.klimafonds.gv.at/wp-content/uploads/sites/6/BGR0102017SC.pdf
[18] https://greenenergylab.at/projects/spatial-energy-planning/  

Figure 3 waste heat potential distribution in Vienna from the most relevant industry sectors

Significant contribution by geothermal energy and seasonal storage

There are efforts to exploit deep geothermal resources in the Vienna Basin[19]. 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 competes with the existing waste incineration plants, Wien Energie is investigating different options for seasonal storage. These include pit storages[20] as well as aquifer thermal energy storages (ATES) and the use of groundwater-bearing geological formations in the deep underground[21].

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)[22]. These high temperatures are key barriers to integrating alternative heat sources; however, technical, economic, and legal obstacles hamper the necessary investments for their reduction. A recent study has shown possible business models encouraging a substantial temperature reduction[23]. Assessing the socio-economic benefits of reduced network temperatures is essential in this context. An analysis of the Austrian DH sector showed savings of 0.426 €/(MWh·°C) or, in absolute terms, 10 million Euros per °C per year when the system temperature in all existing DH networks is reduced[24]. This number can be expected to be even higher for systems with a high share of waste heat, geothermal energy, and seasonal storage [25].

[19] https://www.geotiefwien.at/
[20] https://www.gigates.at/index.php/de/
[21] https://greenenergylab.at/green-energy-lab-startet-mit-17-neuen-innovativen-projekten-und-einem-investitionsvolumen-von-80-millionen-euro-ins-neue-jahr/
[22] http://www.austrian-heatmap.gv.at/fileadmin/user_upload/FW_KWK_Endbericht.pdf
[23] https://doi.org/10.1016/j.energy.2020.116963
[24] Roman Geyer, Jürgen Krail, Benedikt Leitner, Ralf-Roman Schmidt, Paolo Leoni: Energy-economic assessment of reduced district heating system temperatures; Smart Energy (submitted)
[25] Implementation of Low-Temperature District Heating Systems, A guidebook from the IEA technology collaboration program concerning district heating and cooling, IEA DHC Annex TS2 (unpublished)

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[26]. An interesting option for larger refurbishment projects has been demonstrated in the project “Smart Block Geblergasse.” A low-temperature DHC network has been implemented in a block of old buildings[27]. The project AnergieUrban builds upon this experience and investigates different heat supply options for existing buildings[28]. Since heat sources in urban areas are sometimes limited, options for harvesting excess solar heat from building surfaces, sidewalks, streets, and squares are also investigated in research projects[29].

[26] https://www.klimaaktiv.at/service/veranstaltungen/Allgemein/restart-gas-etagenheizung.html
[27] https://www.diepresse.com/5730730/sonne-erde-wind-und-mikroben
[28] https://www.oegut.at/de/projekte/energie/anergie-urban.php
[29] https://nachhaltigwirtschaften.at/en/sdz/projects/heat-harvest.php

Figure 5 Vision of the Heat-Harvest approach for harvesting solar excess heat and re-using it in winter

Graz and Innsbruck

Other cities are currently implementing innovative activities towards the decarbonization of their DH supply as well. Alone frontrunner is Graz, where fossil-fired CHP plants have become uneconomic, and almost 80 % of the overall DH supply must be replaced. Therefore, Graz initiated a stakeholder process, resulting in various decarbonization measures[30]. In this context, Graz was a use case to validate different methodologies for evaluating and mapping the potential of waste heat[31], including an innovative approach using gamification[32]. Another interesting heat source is currently being investigated in Innsbruck: the drainage water from the 64-kilometer-long Brenner Base tunnel between Austria and Italy[33].

[30] https://www.grazer-ea.at/projekte/waermeversorgung-graz-2020-2030/
[31] http://blogs.hawk-hhg.de/memphis/   and  http://cities.ait.ac.at/uilab/udb/home/memphis/
[32] https://cities.ait.ac.at/projects/hotcity/
[33] https://www.tugraz.at/en/tu-graz/services/news-stories/media-service/singleview/article/brenner-basistunnel-als-leuchtturmprojekt-tunnelbauten-sollen-co2-neutrale-energielieferanten-werden/

Figure 6 The drainage water from the Brenner Base Tunnel could supply Innsbruck's city districts with energy in the future. © BBT SE

Wind, Solar, and Milk

One of the regions with the highest wind energy supply in Austria is Burgenland, where two heat pumps have recently been installed in Neusiedl am See’s DH network. The heat pumps are directly connected to a transformer station from a wind park, thus reducing network fees and making the system economically feasible[34]. Austria’s second-largest solar thermal system has recently been installed in Mürzzuschlag, a town of 8,500 inhabitants in a mountain region in Styria. Its DH system used to be fired by natural gas and biomass boilers. The new solar thermal field has a collector area of 5,000 m², resulting in CO2 savings of 930 t/a[35]. In the former “Martinek”-military camp south of Baden, a concept for a low-temperature heating and cooling grid is being elaborated at the moment, using waste heat from the neighboring NÖM dairy plant (milk) as well as locally available renewable heat sources[36].

[34] https://eventmaker.at/uploads/16600/downloads/lehner_vortrag.pdf
[35] https://www.solid.at/en/reference/murzzuschlag.html
[36] https://www.nefi.at/en/sanba/

Figure 7 Austria’s second largest solar thermal system in Mürzzuschlag

Flexibility is key

The expected massive integration of renewable sources in the electricity grid represents a challenge in the energy system due to their stochastic character. Investigating different integration options of heat pumps in Austrian DH networks has shown that heat generation costs can be reduced by taking advantage of low prices in the day-ahead market, and additional revenues can be generated in the balancing market[37]. This concept is further investigated and scaled for the region of lower Austria[38].

Conclusions and outlook

Current decarbonization strategies in the DH sector foresee mainly renewable fuels. On the other hand, many innovative projects, including heat pumps, waste heat, and geothermal energy, are currently carried out, including seasonal storage. A recent draft of the new renewable expansion law includes a mandatory development of a decarbonization pathway if applying for investment funding for DH networks. Further on, the concept of energy communities should be expanded to the heating sector. In any case, the future of DH in Austria has many promising options!

[37] https://doi.org/10.1016/j.energy.2019.116875
[38] https://www.ivl.se/projektwebbar/flexi-sync.html

For further information, please contact: Ralf-Roman Schmidt, Ralf-Roman.Schmidt@ait.ac.at

Meet the authors

Ralf-Roman Schmidt
Senior Research Engineer bei AIT - Austrian Institute of Technology
Edith Haslinger
Senior Scientist bei AIT - Austrian Institute of Technology
Roman Geyer
Designing Innovative Energy Systems, Wien Energie GmbH
Benedikt Leitner
Senior Data Scientist at Wien Energie
Dragisa Pantelic
Project Lead Innovative Energy Systems, Wien Energie GmbH
“Decarbonization of the Austrian District Heating systems” was published in Hot Cool, edition no. 1/2021. You can download the article here: