Comparative test of two large solar collectors for solar field application

摘要

Two large flat plate solar collectors for solar heating plants were tested according to the standard norm EN 12975-2. The two collectors were almost identical, the only difference being a thin FEP (fluorinated ethylene propylene) foil interposed between the absorber and the glass cover in one of them, in order to decrease convection losses. The efficiencies of the collectors were tested for different flow rates and tilt angles. The effect of the change from laminar to turbulent regime was investigated as well. Numerical models of the two collectors were developed with the software Soleff and their results were compared to the experimental measurements. The experimental results showed that the FEP foil caused a decrease in the optical efficiency of 2-4 percent. Nevertheless, the collector with the FEP foil performed better when the mean temperature of the solar collector fluid was sufficiently high. Additionally, the collector efficiency of both collectors increased at higher flow rates and tilt angles. The models developed in Soleff fit the experimental results with an average error of 1% in case of fully laminar and turbulent flow, so that they are likely to be suitable to simulate the collector performances in untested conditions. On the other hand, the software proved to be inadequate to study the collector efficiency in the transition region between laminar and turbulent regime.