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Large collector fields are increasingly being integrated into district heating systems. Due to the operation mode of these networks, the solar system must provide the desired supply temperature. Therefore, knowledge of thermal-hydraulic behavior and energy efficiency are very important for planning, operation and control. The study presents the investigation of two large-scale solar collector fields in Chemnitz (Germany). For the detailed study of heat transfer and hydraulic behavior of the field, mobile monitoring has been installed on selected rows in addition to the conventional monitoring system. The measurement results show that large collector fields with differently sized rows, consisting of a large number of collectors with a dividing manifold (below) and a combining manifold (above) connected to a large row, can be operated with a variable flow rate (matched flow). With the provided measured values, comparison of the desired/actual values and the calculation of absolute and relative parameters are performed. The Brühl solar district heating system has been in operation since summer 2016 and meets the expectations of thermal performance and efficiencies.
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