Vienna builds heat recycling system at local natural spa

The renewable energy system at Therme Wien will use wastewater to provide heat for 1,900 homes

This week, authorities in Vienna announced that Wien Energie, the city’s energy company, has set up heat pumps in one of the natural thermal water pools in the Austrian capital. Said pumps will collect heat from wastewater and feed it back to the district heating system, providing green energy for 1,900 households in the Oberlaa district.

Using every ounce of energy

The heat recycling system was installed in the Therme Wien thermal bath, located at the district's edge. A company owned by the city operates the spa site itself. The baths were first opened in the 1950s and fairly recently, in 2009, they were expanded to feature two natural sulphur springs. Therme Wien is a massive complex, as it offers 72,000 square metres of spa space, with 4,000 square metres of water surface, 3,000 square metres of saunas and more.

The pumps will take advantage of the water after it passes through the facility. Before the alternative energy system was installed, that water was just drained into the sewer system but now, via a process the city has dubbed ‘reverse refrigeration’ it will be a part of Vienna's renewables ecosystem. The water has a natural temperature of 30 degrees Celsius, but the system will be able to reach a level of 85 degrees before the energy can be fed back into the district heating system.

That green heat will be able to meet the demand of 1,900 homes with a rough annual energy production estimated at 11-gigawatt hours. It is also estimated to save up to 2,600 tons of CO2 per year. At the same time, the project will cost Wien Energie 3 million euros, in what CEO Michael Strebl has deemed a step towards energy independence and climate neutrality.

City Councillor for Economics, Peter Hanke, was quoted in a press release, saying: “It is precisely because of such solutions that Vienna is a model climate city! Here, Wien Energie uses valuable waste heat from the thermal water of Therme Wien to generate district heating. The project is another building block for climate protection and an important step towards greater independence from gas imports.”