Modellering av inmatningscentral för småskalig värmetillförsel till fjärrvärmenät

Sammanfattning: The district heating sector is moving into a new era which brings lower temperatures in the heating network which in turn opens up for a more extensive use of low grade heat such as solar heat. This project aims to develop a dynamic simulation model for feeding centrals in order to be able to design and optimize systems for decentralized feeding regardless of heat source. The big challenge lies in reducing and eliminating the power swing of the feeding which occurs as a consequence of the high pump pressure that is required in this type of establishment. The modelling part is designed in Simulink which is a simulation environment with a graphical interface coupled with the programming language MATLAB. The model is initially aimed on two system configurations that consist of a circulation pump and one alternatively two two-way valves. The feeding central is connected in-between the return- and feed pipe in order to obtain the highest efficiency of heat transfer. A few existing Simulink-blocks have been used as a base for the model after some modification. Two field studies to feeding centrals have been made in association with development of the model, one to Ödåkra and one to Avedöre, Denmark. These both feeding centrals use solar thermal heating as heat source and are using a pump together with one two-way valve. The difference between the two systems is that the establishment in Avedöre includes storage tanks for heat storage. These field studies were carried out to give further knowledge of the feeding central design as well as to obtain data for verification of the model. Data from the field study in Ödåkra has been used to verify the model. The simulations give good results even as there is room for fine tuning of the model to give an even better interpretation of reality. The most probable reason for the deviations is that the material data used in the model concerning valves, pipes and heat exchanger differ from the ones used in Ödåkra. Additionally, limits in Simulink have contributed to approximations of physical relations that may have influenced the results. The greatest deviation appears during valve regulation where a relatively large offset of mass flow occurs. After investigation, even this seem to be connected to the material data used. In order to be able to generate satisfying results, the model need further development.