Research on dynamic thermal characteristics of district heating systems based on return temperatures at heat sources

The dynamic thermal characteristics (time delay and heat loss) of district heating systems (DHSs) affect the operational regulation and energy saving of the systems. Limited by the ability of the established dynamic thermal models to simulate return temperatures at heat sources, previous studies have mainly focused on the dynamic thermal characteristics of supply networks by simulating the supply temperatures at substations; however, the dynamic thermal characteristics of the entire DHSs, mainly represented by the characteristics of the return temperatures at the heat sources, have rarely been focused upon. This study presented an integration model that was capable of completely simulating the dynamic thermal conditions of DHSs, including the return temperature at the heat sources. In addition, the accuracy of the integrated model was validated by comparing the simulated and measured return temperatures at the heat source on a real DHS in terms of the heat loss and delay time in the process of temperature transfer. Moreover, based on the validated integration model, the dynamic thermal characteristics of the entire DHSs were analyzed. The validation results showed that the simulations of the integration model were consistent with the measured return temperature at the heat source; the average absolute and relative errors were 0.85℃ and 2.1%, respectively, while the deviation of the delay time was within 10 min. Furthermore, the results of the characteristic analysis indicated that the delay time of the return temperatures at the heat source was approximately twice that of the supply temperature at the farthest substation, and the delay time of the temperature transfer in the DHS was approximately 21–24 min/km.