Development and validation of a detailed TRNSYS-Matlab model for large solar collector fields for district heating applications

This study describes the development of a detailed TRNSYS-Matlab model to simulate the behavior of a large solar collector field for district heating application. The model includes and investigates aspects which are not always considered by simpler models, such as flow distribution in the different rows, effect of the flow regime on the collector efficiency, thermal capacity of the components and effect of shadows from row to row. The model was compared with measurements from a solar collector field and the impact of each aspect was evaluated. A good agreement between model and measurements was found. The results showed that a better agreement was achieved, when a flow regime-dependent efficiency of the collector was used. Also the precise flow distribution in the collector field improved the model accuracy, but it must be assessed if the aimed level of accuracy justifies the much longer programming and computing time. Thermal capacity was worth being considered only for the bulkier components, such as the longer distribution and transmission pipes. The actual control strategy, which regulates the flow rates in the solar heating plant, was accurately reproduced in the model, as proved by the good agreement with the measurements.