Heat transfer modelling of the Leibnitzer Feld aquifer, Austria

The impact of groundwater heat pumps on groundwater temperature is simulated by means of a 2D numerical groundwater model in the Leibnitzer Feld aquifer, Austria. The model provides a basis for assessing the regional use of groundwater temperature as an energy source. Since the groundwater table is shallow, the air temperature represents the main source controlling the groundwater temperature. A temperature input function depending on the depth of the groundwater table is delineated from an observed soil temperature profile and the air temperature. Given the diffuse and ubiquitous nature of the heat input, the heat exchange is implemented as a third type boundary condition to enable two-way heat transfer. The temperature of the reinjected water is limited to a decrease of 5 K and an absolute minimum of 5 degrees C by Austrian law. The pumping rates needed to cover the heat requirements of three typical users are determined for selected locations. It is shown that the reduction of the ambient groundwater temperature approximately 300 m downstream of the reinjection wells is less than 0.5 degrees C. Thus it can be concluded that aquifers in similar settings show substantial potential to provide heating and warm water supply for buildings without deteriorating the regional groundwater temperature regime.