Improved thermal transient modeling with new 3-order numerical solution for a district heating network with consideration of the pipe wall's thermal inertia

An improved thermal transient model was put forward to predict the thermal transient behavior of a long pipe. The model took particular consideration of the influences of the pipe wall's thermal inertia. Then a new 3-order numerical solution was presented to solve the proposed model. The new solution would not only preserve the sharp temperature front during the heat propagation, but also achieve fine computational accuracy even for the coarse grids. In addition, the proposed model and numerical solution could be easily coupled with enormous common hydraulic models to be available to a general district heating (DH) network. The model and solution were validated in a real DH system. The simulation results had a good agreement with the measured data. Furthermore, in order to quantify the degree of the influence of pipe wall's thermal inertia, a practical indicator was developed based on ten types of often-used pipes in the DH projects. The research results showed that, for the large pipes with diameters over DN 200, the simulation errors caused by neglecting the pipe wall's thermal inertia were no more than 10%, which meant it was unnecessary to consider the thermal inertia for larger diameter pipes during the process of modeling.