On Hydraulic Constraints in Control of District Heating Systems

Sammanfattning: District heating systems make an important puzzle piece in the energy system of both today and tomorrow. When designing, simulating and controlling these systems, hydraulics play a vital role. The pressure generated by pumps has to drive sufficient flow throughout the system to satisfy the requirements of customers. Ensuring that the system is sufficiently pressurized is a challenging task already in current systems, and may become even more challenging in the transition to the 4th generation of district heating. In the first paper of this thesis, a demand response framework is suggested, which distributes the available flow to customers in a fair way. The framework aims to make it so that when the available pressure in the network is low, the buildings in the periphery should still be able to satisfy their heating needs. The second paper of this thesis extends previous methods for identifying greybox parameters for hydraulic district heating models. Previous methods of this type rely on more measurement points, and do not include the influence of the control valves situated in customer substations. These model parameters can then be used for simulation or control purposes. Together, the results presented in this thesis provide tools for better dealing with the hydraulic limitations in district heating systems. At the end, future work is outlined which may further pave the way for improved control that takes hydraulic limitations into account.