Thermo-hydraulic coupled analysis of long-distance district heating systems based on a fully-dynamic model

Abstract

The long-distance district heating pipeline (LDHP) system is a key solution for transporting the renewable heat from the suburban to urban areas. In LDHP, thermal and hydraulic characteristics are coupled. Developing effective thermo-hydraulic co-simulation method is vital to enhance LDHP’s operation performance and to enhance its flexibility. As the pressure wave travels much faster than the hot water in the district heating (DH) pipeline, the research in this regard mainly focuses on pseudo-dynamic model, in which the calculation of thermal dynamics only adopts the static hydraulic conditions. In this paper, a novel fully-dynamic model considering both the hydraulic transients and thermal dynamics is developed. The model is solved using the method of characteristic (MOC). The optimal spatial and temporal step sizes for the thermal dynamic modeling are analyzed and studied. Next, we compared our proposed model with the conventional pseudo-dynamic model on a 20 km LDHP. Results show that the simulated temperature fluctuations of the two models are close to each other, but the predicted temperature arriving at the heat exchange station is up to 28 s earlier than the pseudo-dynamic model, indicating that hydraulic transients have some influence thermal dynamics. Moreover, the fully-dynamic model has capability to predict the temperature and flow rate transport of the system in both disturbance state and steady state, which is important for the rapid and accurate analysis of the operation of LDHP.