Flat plate thermal solar collector efficiency: Transient behavior under working conditions part II: Model application and design contributions

An experimental research was performed on a solar facility with a nine-year-old, on-campus field with 50 m2 area of flat plate solar collectors. A transient model was developed, adapted to the characteristics of this facility and experimentally validated as described in Part I of this paper. The efficiency normalization curve (ENC) operating conditions for the steady-state test are different from the working conditions. Significant differences between the ENC and the model based predictions were found and quantified. The significance of the transient behavior is compared with the thermal inertia proposed in the EN-12975:2006 standard for the quasi-dynamic test. Using the model capabilities to predict the collector performance under transient working conditions, the influence of the operating conditions on the collector efficiency and on the useful heat produced is studied individually. The relevance of those conditions is ranked as follows: the wind (velocity magnitude and direction) was the most influential, followed by the aging of the collector surfaces, convective heat losses, thermal inertia and the incident angle of irradiance.