Integration of solar thermal systems into existing district heating systems

Abstract

Modern district heating (DH) networks are usually operated with a changing flow temperature to cover the heat load of the supply area, depending on the outside temperature. Due to the minimum temperature requirements of individual customers, DH networks also need to operate during the summer months. During this time, the load on the system is relatively low. This requires combustion facilities to operate on low load levels as well. These systems have a potential of improving the energy efficiency by utilizing other energy sources such as waste heat from industrial processes or solar thermal systems. The overall aim of the presented work is to provide a new methodology for the integration of solar heat into existing DH systems.The feasibility of including solar thermal systems in existing DH networks will be analyzed, based on the state of the art of solar DH. The main focus will be on large DH systems that are mainly supplied by fossil fuel powered combined heat and power (CHP) plants considering how such plants can be operated in the future. In this paper, characteristic technical and ecological key performance indicators of a transformed DH system will be displayed.The work was carried out based on real data of an example DH network in Germany. It was analyzed how a sub-network of a system can be supplied during the summer season by a solar thermal system as far as possible independently from the main-network without using a back-up boiler system. The favored solution in this article is to use a thermal storage that can be recharged once a day by a central CHP plant.