Modeling, quantification and enhancement methodology for energy storage in load-concentrated district heating systems

District heating systems can act as passive thermal storage that supports power system regulation, but realizing this value calls for rigorous quantification and purposeful enhancement. This study develops an improved district heating network model based on a one-dimensional pipe formulation, representing axial heat conduction, heat dissipation, and a calibrated initial temperature field to capture spatial inhomogeneity. Using numerical simulations without field or experimental validation at present, storage performance is assessed in both heat source failure and flexible heating scenarios using clear, operational notions of maximum heating duration and maximum heat storage duration. For a representative system, raising the circulating water flow rate lowers the overall temperature level of the network and, when combined with variable flow operation that actively stores heat on the user side, yields a markedly longer period of sustained heating during source outages. To unlock flexibility, an enhanced flow-temperature regulation method is proposed that greatly broadens the range of heat source heat flow variations the system can tolerate within a day; this benefit remains under a stricter upper water temperature limit, although the admissible range is smaller than under a more permissive limit. Overall, coordinated flow control converts thermal inertia into usable storage, and the proposed regulation substantially increases admissible source side variability, enabling integration of low temperature heat sources and the provision of grid support services by district heating systems.