MUSE pilot area activities – RESULTS – #9 Vienna

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Identifying underground urban heat islands in Vienna using groundwater temperature measurements

C. Steiner (GBA), 18 August 2021

Field measurements for MUSE in the pilot area Vienna focused on the shallow groundwater body, which consists of gravelly river sediments, on the right side of the river Danube. There are many different anthropogenic heat sources expected in this urban environment. In order to increase the knowledge of possible urban heat islands in the pilot area, we conducted groundwater temperature measurements in eight boreholes. The selected boreholes are located in the vicinity downstream of large known groundwater heat exchangers. Goal was to demonstrate the impact of the systems to the groundwater temperature. An analysis of temperature time series in the city of Vienna revealed a mean annual temperature of around 13 °C. In three study sites (Erdberg, Prater and Praterstern), we intended to quantify the urban heat island effect compared to this overall value of Vienna.  Figure 1 shows the location of the boreholes inside the pilot area of Vienna. 

Figure 1: Overview of pilot area Vienna including the three case-study sites Praterstern, Prater and Erdberg as well as existing shallow geothermal energy installations (GWHE – groundwater heat exchanger) and boreholes with groundwater temperature measurements conducted by Geological Survey of Austria and Municipal department for Vienna Waters (MA 45).

The investigated boreholes were equipped with in-house developed loggers to measure the groundwater temperature in multiple depths and water level data loggers (have a look at our measurement equipment here).

At Erdberg we focused on one large building, which uses a groundwater heat exchanger for heating and cooling as well as borehole heat exchangers. Here we saw a large impact in the close vicinity of around 200 m on the groundwater temperature (temperature increase of up to 3 °C) and even in 700 m away from the injection well, the groundwater temperature is still elevated of 1 °C. Over the year, the influence of the shallow geothermal energy (SGE) use is prevailing from May to October, as figure 2 shows.

Figure 2: Groundwater temperatures (yellow, orange, brown) and water level (pink) in the vicinity of the groundwater heat exchanger in Erdberg.

In the area Prater the expectations of a large thermal plume caused by a groundwater heat exchanger using 150 l/s for the Economic University of Vienna were not fulfilled. The investigated boreholes are situated outside of the thermally influenced area. The groundwater temperatures in the area Praterstern show an impact of the metro line nearby, they are increased up to 2 °C compared to the mean groundwater temperature in Vienna.

Our field measurements show that anthropogenic heat sources influence the temperature very locally, and a dense monitoring network is necessary to identify and more accurately delimit urban heat islands. The follow-up project “Heat below the city” intends to create a temperature map with high resolution for the identification of underground urban heat islands in Vienna. Management plans can integrate this temperature map for an efficient use of groundwater for heating and cooling and furthermore to counteract even the development of urban heat islands by intensified use for heating.

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