A quasi-dynamic model and comprehensive simulation study of district heating networks considering temperature delay

In district heating networks (DHNs), the water temperatures supplied to the users are often delayed relative to the heat source conditions due to distant pipeline transportation. The exclusion of time delays causes inaccuracy in estimating user supply temperatures with steady-state models. In this work, a quasi-dynamic model is proposed to estimate hydraulic and thermal conditions of heat networks. For each timestep of the simulation, the transport time delays from the heat source to the users are calculated according to flow conditions, and the users’ supply temperatures are derived by tracing the historic heat source temperatures. Moreover, the models for heat substations and radiators in buildings are incorporated with the primary pipeline model for comprehensive system simulations. An iterative solver based on the Newton-Raphson method is developed to address the coupled hydraulic-thermal equation system. An existing university campus heat network is case-studied, and the measured operation data is used for model validation. The proposed quasi-dynamic model demonstrates an improved supply temperature estimation accuracy compared with the steady-state model, with 20 % less of the average rooted mean square error. It also offers comparable accuracy to Dymola and COMSOL simulations with reduced computation time. In addition to model validation, system simulations are conducted to investigate future DHN scenarios with low operating temperatures. The findings suggest that the network heat loss is related to both the primary and secondary temperature levels, and a reduction in the primary temperature alone may increase heat loss. • A quasi-dynamic hydraulic-thermal model for district heating networks is developed. • The user's supply water temperatures are delayed from the heat source. • A university heat network is case-studied and measured data is used for validation. • Heat networks with lower temperatures in secondary loops have less heat loss.