Control Aspects of Decentralized Solar Thermal Integration into District Heating Networks

This paper consists of two parts. In the first part a numerical model describing the thermo hydraulic behavior of district heating (DH) networks has been used to investigate the pressure and temperature profile within a solar assisted system. The network description is based on a graph-theoretical method and the Newton algorithm was used for solving the system of nonlinear equations. A direct integration without heat storage is implemented here for an existing network topology in South Germany. The simulation shows that critical differential pressure driven operation of the district pump is not realizable with a reasonable number of pressure transmitters. The volume flow driven control provides more stability but has to be optimized by means of pressure measurements. The second part of the paper presents the new test facility built for decentralized solar heat integration. It also gives an overview about the design topics that will be investigated during the next test period: component suitability for bidirectional heat exchange, station control, net metering and handling both solar and load sides.