Cooling Potential of the Warta River in Poznań (Poland) for Sustainable Energy Systems: Determinants and Seasonal Variability

The smart city concept promotes the use of innovative solutions to improve residents’ quality of life while supporting sustainable urban development. In the context of climate change and rapid technological advancement, there is a growing demand for energy-efficient cooling systems that use natural resources. This study evaluates the influence of the hydrological regime of the Warta River on its cooling potential in Poznań, one of the largest cities in Poland. Based on hydrological data collected between 1971 and 2024, the distributions of river discharge and water temperature were analysed, as these represent the two key parameters determining the feasibility of river-based free-cooling systems. Considering environmental flow requirements and water temperature thresholds, several operating scenarios were developed to simulate cooling capacities of 100, 150, and 200 MW at temperature differences (ΔT) of 3 and 5 K. Among the analysed variants, the lowest cooling demand scenario (100 MW, ΔT = 3) provided suitable operating conditions for a river-based free-cooling system during 10,582 days, corresponding to 53.6% of the study period. In contrast, the highest cooling demand scenario (200 MW, ΔT = 5) was feasible during 43.9% of the analysed period. The results indicate that the Warta River has considerable potential as a natural cooling source for free-cooling applications, although this potential exhibits pronounced seasonal variability. The highest cooling capacity can be achieved during spring and autumn, while lower capacities are available in summer and the lowest in winter. River water temperature was identified as the dominant limiting factor, accounting for approximately 96% of all cases in which free-cooling operation was not feasible. Furthermore, the observed increase in river water temperature has reduced the number of summer days during which the required cooling capacity can be achieved. The findings enable the identification of periods when river water can fully or partially replace conventional mechanical cooling systems. They also provide a framework for assessing the seasonal and operational potential of surface waters in support of future investments integrating rivers into urban cooling infrastructure.