Urban Technology: Power Beneath the Drain Cover

A pilot project for accessing a new source of power for heating and cooling buildings utilises waste water in Vienna's sewage network. The City of Vienna is checking further locations up until 2008. Large companies will also be offered access to the system.

Unutilised power potential

Whenever in winter steam rises out of the drain covers an unused source of power goes to waste. "What has been missing so far is the technology to tap this treasure", said Environment City Councillor Ulli Sima. And now Austria's first-ever plant for deriving power from the public sewage system is being presented. It is located in the operating branch of Municipal Department 30 - Wien Kanal - in the district of Liesing.

Heat exchange

In principle the system makes use of the temperature difference between the water and the surrounding air. Waste water in the 3,200 km Vienna sewage system has an average temperature of 16°, and even in winter it is not below 12°. Thanks to the discharge from showers, bathtubs and washing-machines a lot of hot water flows into the sewage system. Over a distance of 30 meters below the operating branch a heat exchanger has been installed in the sewer there. A heat pump raises the temperature of the water to around 35°.

Eco-friendly

The plant heats one-fifth of the approximately 5,000 sq.m. building in winter and helps with the warm water heating. In summer the opposite effect is used for cooling. This enables the MA 30 to save about € 12,000 a year in this location alone. The thermal power production amounts to 366 megawatt p.a. Compared to an oil heating of the same capacity about 80% less greenhouse gases are produced and the "source of power" is virtually inexhaustible. The cost of installing the plant amounted to € 150,000.

More plants in future

In collaboration with Vienna Technical University up until spring 2008 tests will be conducted to see how the plant's energy output can be enhanced. At the same time MA 30 is looking for additional sights in Vienna where similar plants would be technically and economically efficient. The prerequisite is a through-flow of 90 litres per second in the particular sewage sections. As from autumn 2006 the system will also be offered to large companies for their own energy needs.

Link-Tipp

Municipal Department 30 - Wien Kanal Vienna Technical Universit