Results of groundwater heat exchanger monitoring in the urbanized area of the city of Zagreb

S. Borovic (HGI-CGS), 19 July 2021

Zagreb, as other large urban areas, has significant heating and cooling demand, and it is clear that many investors opt for the installation of different types of heat pumps. Unfortunately, the number of installed heat pump systems is not known as there is no organised register and the regulations on construction are becoming more lenient, rather than stricter.

In the scope of MUSE we wanted to examine if the open loop systems cause thermal pollution in the Zagreb aquifer, which is also the source of public water supply, and if that is the case, what is the magnitude. We monitored two sites: one is a residential building, while the other is a large IKEA store with accompanying facilities. Due to significant extent, thickness and favourable hydrogeological parameters of the aquifer, our hypothesis was that we will not observe significant temperature deviations.

As can be observed from the figures, the groundwater levels and temperatures show a normal annual variation. The amplitudes are small and in accordance with the seasonal data for Zagreb alluvial aquifer. The temperature amplitude was only 2.2 °C in Veslačka, and 1.83 °C in IKEA, while the recorded amplitude in the nearby observation well of the Croatian water management authority closer to Sava River is 5.5 °C.

Since we have engaged in a small-scale pilot activity, the monitoring results are expected. However, we tested a hypothesis and confirmed it, so we can be more confident in our future assessments.

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