A new quasi-dynamic load flow calculation for district heating networks

District heating networks can serve as large heat reservoirs due to thermal inertia. To analyse the behaviour of these networks, a load flow calculation must be performed. There are three basic approaches available for this purpose. One is the steady-state approach, which cannot consider the temporal temperature distribution. Another one is the dynamic approach that considers the thermal inertia of district heating networks, but it has a high computation time. The presented method uses a quasi-dynamic approach, which can provide a faster calculation time than dynamic approaches and can also consider thermal inertia. This method is based on a Lagrangian specification approach which shows better performance than Eulerian specification approaches but is more complex to implement. The validation of the method indicates that the accuracy is high and, therefore, acceptable. The computation time of the method is several times faster than dynamic approaches and slightly slower than steady-state approaches. However, with quasi-dynamic approaches, it has not been possible to compute networks of arbitrary size and complexity. With the method described in this paper, this is now possible. Furthermore, due to its properties, the method can be well integrated into calculation methods of multi-energy-systems.