Computer Model of the Philips Evacuated Tubular Solar Collector Used in the CEC5 Round Robin Test Series

Summary

The fifth round robin test series of the CEC solar collector testing programme used a Philips evacuated tubular collector. A computer model based on a one-dimensional, steady-state heat transfer analysis of the collector module was developed to aid theoretical understanding of its heat transfer processes and to normalise test data to standard operating conditions. Model-predicted collector performance characteristics are in excellent agreement with the CEC5 round robin test results, for both kinds of diffuse back reflector used in the test series. The effects of variations in local wind speed, effective sky temperature, percent diffuse irradiance and collector tilt angle (for angles in the range 25°–65°) are estimated to be small. Because the absorber fins and heat pipe evaporators in the collector module are well isolated from the environment, their heat transfer processes are only weakly influenced by variations in environmental conditions. It is concluded that the observed scatter in the round robin test results, which was found to be non-reducible by normalisation, is therefore probably attributable to instrument calibration errors, and to heat losses through cracked glass envelopes and gaps in the header insulation