A modeling approach for district heating systems with focus on transient heat transfer in pipe networks: A case study in Studstrup, Denmark

Increasing the building energy efficiency in recent years results in noticeably reduction in their heating demand. Combined with the current trend for utilizing low temperature heat sources, it raises the necessity of introducing a new generation of district heating [DH] systems with lowered operational temperature. However, in order to implement low temperature concept for existing DH systems, there is a need to apply a stepwise changes in the existing systems. This study emphasis on improving the existing DH pipes networks. For this purpose the first step is developing a model, which comprises district heating networks [DHN] characteristics.
This paper is presenting a new developed model, which reflects the thermo-dynamic behavior of DHN. It is designed for tree network topologies. The purpose of the model is to serve as a basis for applying a variety of scenarios towards lowering the temperature in DH systems. The main focus is on modeling transient heat transfer in pipe networks regarding the time delays between the heat supply unit and the consumers, the heat loss in the pipe networks and the consumers’ dynamic heat loads. A pseudo-dynamic approach is adopted and also the implicit finite element method is applied to simulate transient temperature changes in pipe networks. The model is calculating time series data related to supply temperature to the DHN from heat production units, heat loads and return temperature related to each consumer to calculate dynamic temperature changes in the network, heat loss and temperature loss through the pipe networks. To validate the model and to demonstrate its competences, the model is applied for Studstrup district heating networks. Studstrup is a suburban area in Aarhus, Denmark where 320 consumers are connected to the DHN through approximately 14 km pipelines (supply and return pipes). At the first stage, the Studstrup DH system is developed in TERMIS, which is commercial software for district heating system simulation, and then the developed model is validated and compared with the results obtained from TERMIS and measurements. The TERMIS model is already validated towards measurements.
This paper explains the developed model, which is going to be used for performing possible scenarios to improve the existing DHN from heat and temperature loss viewpoints. Moreover, it provides a platform to add and extend different aspect of DH systems.