Thermal modelling of a flat plate solar collector with latent heat storage validated with experimental data in outdoor conditions

This paper presents a thermal modelling strategy to evaluate the performance of latent heat storage technique in a flat plate solar collector (FPSC) with integrated phase change material (PCM). A thermal dynamic model is developed based in simplified semi empirical correlations and includes heat transfer by conduction, convection and radiation in each part of the device. Melting process of the PCM is described with energy balances for a set of discrete spatial layers to calculate temperature and liquid fraction. The model is validated with experimental data gathered under outdoor conditions from a real flat plate solar collector prototype modified to incorporate PCM containers between the absorber plate and the insulation. As result of the validation process, the model shows the capability to estimate the global thermal performance of the device with good accuracy compared with the experimental measurements and using minimal computational resources. Comparisons between estimations of the model and test data are presented for 20 days, real conditions include days with both high and low incident radiation and two different PCMs. Predicted temperature of glass cover, absorber plate, water outlet and PCM are obtained with a maximum error of 4.62%. The model was employed to analyze the collector thermal performance. Temperatures, heat transfer, stored energy of collector main components and liquid fraction of PCM are estimated and analyzed in two cases: under clear sky condition without strong changes of solar radiation and under scattered weather with solar radiation variation. Two PCMs with different melting points (45 degrees C and 60 degrees C) are analyzed and compared with results without PCM by using the model to evaluate their performance.