Improved District Heating Return Temperatures by Cascading Concepts

Abstract As the focus on the performance of district heating (DH) systems intensifies, this study explores three cascaded substation concepts to assess their potential for reducing the DH return temperature at the building level substation. A lower DH return temperature is crucial for lowering the DH flow temperature to optimal levels, thereby enhancing system efficiency, which is a key feature of 4th generation DH (4GDH). Within the ARV project ( https://greendeal-arv.eu ), DH substation concepts have been evaluated, including parallel, two-stage, aftercooling, and midcooling configurations, with the parallel concept serving as the baseline for comparison. The analysis, based on annual simulations, covers generalized parameter combinations to demonstrate the potential for DH return temperature reduction across the different substation concepts in comparison to the baseline. Additionally, the impact of various climate profiles is explored, represented by the locations of Copenhagen, Helsinki, Paris, and Rome. Field data from a two-year test of the aftercooling concept validates the analysis results. The aftercooling and midcooling concepts have a significant reduction potential in annual DH return temperatures by 3 to 9,5 °C for 4GDH operations, compared to the baseline system.