Dynamic thermal models and CFD analysis for flat-plate thermal solar collectors - A review

The detailed analysis of a solar collector is a complex task, due to the high number of parameters affecting its performance. In the last 40 years, several dynamic procedures have been developed and tested using numerical approaches, to obtain the behavior of the thermal solar collector without performing the set of complicated and expensive experimental tests usually adopted in steady-state approaches. Moreover, thanks to the improvement of the computing performance, these numerical models provide useful tools in reproducing for complex system behavior. In fact, when multiple energy sources are coupled together to build integrated systems (i.e., Solar-Assisted Heat Pumps, Ground-Source Solar-Assisted Heat Pump, etc.) the dynamics of each equipment has an noticeable influence on the behavior of the whole system. Therefore, these tools can be also profitably used to develop and optimize dynamic control criteria for these systems. In this context, a great effort has been made in the last years to improve the predictive potential of the dynamic models for solar collectors. Finally, thanks to the increase of the computational performance in the last years, Computational Fluid-Dynamics (CFD) approach has become a powerful tool to investigate the heat transfer phenomena. A lot of works have been made using both commercial and in-house developed codes, investigating several aspects concerning the heat transfer mechanism in a solar collector. In the present work, an updated review of models for flat-plate thermal solar collectors is presented, including a proper classification and a description of their main characteristics and performance. A short description of the main works involving CFD analysis on thermal solar collectors is reported too.