High-level numerical modeling of complex heating loops with heat pumps and Thermal Energy Storage for energy flexibility analysis

Heat pumps are key to reducing building CO2 emissions and supporting EU decarbonization goals, but fully exploiting their potential requires integration with Thermal Energy Storage (TES) systems. Accurately analyzing their dynamic behavior and energy flexibility demands high resolution, dedicated dynamic models; by capturing component interactions and transient phenomena during operational transitions, such models can reveal flexibility potentials undetected in steady state simulations. This paper presents an open source Python model integrating water to water heat pumps (WSHPs) with sensible TES. Serving as a preliminary modeling framework, this work lays the foundation for a future digital twin of the HPFlexLab, an experimental facility at the Energy Department (DENERG) of Politecnico di Torino dedicated to advanced building energy management. Results demonstrate the model’s ability to reproduce real system behavior across all operating regimes. Validation against an equivalent Modelica model shows that TES temperature profiles exhibit an RMSE below 0.30 °C, a maximum MAE of 0.22 °C, and an MBE up to 0.09 °C; meanwhile, another plant temperature profile of interest yields RMSE, MAE, and MBE values up to 2.19 °C, 0.51 °C, and 0.15 °C, respectively, depending on the operating mode. Furthermore, the Python code is 3 to 9 times faster than Modelica depending on the simulated operating mode and simulation duration. Finally, multiple day energy simulations reveal that the proposed cost minimized control strategy reduces plant operating costs by 5.0% compared to a reference case without TES, despite increasing energy consumption by 10.5% and carbon emissions by 5.7%. Conversely, an emission minimized strategy fails to lower environmental impacts, resulting in an 11.7% increase in electricity consumption and a 1.4% increase in carbon emissions. Consequently, for this case study, TES integration consistently deteriorates both energy consumption and environmental impact compared to the reference configuration.