Accuracy of the European solar water heater test procedure. Part 1: Measurement errors and parameter estimates

Abstract

The Collector and System Testing Group (CSTG) of the European Community has developed a procedure for testing the performance of solar water heaters. This procedure treats a solar water heater as a black box with input-output parameters that are determined by all-day tests. In the present study we carry out a systematic analysis of the accuracy of this procedure, in order to answer the question: what tolerances should one impose for the measurements and how many days of testing should one demand under what meteorological conditions, in order to be able to guarantee a specified maximum error for the long term performance? Our methodology is applicable to other test procedures as well. The present paper (Part 1) examines the measurement tolerances of the current version of the procedure and derives a priori estimates of the errors of the parameters; these errors are then compared with the regression results of the Round Robin test series. The companion paper (Part 2) evaluates the consequences for the accuracy of the long term performance prediction. We conclude that the CSTG test procedure makes it possible to predict the long term performance with standard errors around 5% for sunny climates (10% for cloudy climates). The apparent precision of individual test sequences is deceptive because of large systematic discrepancies between different sequences. Better results could be obtained by imposing tighter control on the constancy of the cold water supply temperature and on the enviromment of the test, the latter by enforcing the recommendation for the ventilation of the collector.