Usable thermal energy stored in the district heating system for peak shaving: A dynamic simulation study

The operational efficiency of district heating system (DHS) relies on the effective use of stored thermal energy, which spans from heating sources to heat users. Enhancing the operational flexibility of the combined heat and power (CHP) unit necessitates a quantitative evaluation of DHS's usable thermal energy storage to optimize its utilization over time. This evaluation is subject to variability due to the scale, topological structure, and dynamic behaviors of the DHS, presenting a complex challenge. Therefore, the maximum maintenance time and room temperature recovery time were defined as indicators to estimate the usable thermal energy of the DHS for peak shaving in this study, and the dynamic DHS models were constructed for this purpose. Simulations reveal that upon cessation of heating steam flow, standard indoor temperature requirements can be preserved for approximately 2 h. These models facilitate the determination of the optimal maximum maintenance time for various scenarios, thereby maximizing thermal energy utilization within the DHS. Additionally, an analytical derivation of a simplified model for maximum maintenance time calculation, suitable for integration with control systems, is presented. The deviation of this model from actual values is below 10%.