Assessment of the Partial Model Stability of the Quasi-Dynamic Collector Test Under Outdoor Conditions EN 12975 by the Application of Uncertainty Analysis

Outdoor collector tests are inherently performed under variable weather conditions. Whereas ISO 9806 sets strong restrictions for the conditions of usable data sets for the steady-state collector test SST, EN12975 allows more variable ambient conditions for the quasi-dynamic collector test QDT. This results in shorter collector test times, but could have drawbacks for the uncertainties including the reproducibility of the test results, i.e. the parameters of the collector model. As the weather conditions are never the same within several tests, outdoor collector tests are not repeatable only reproducible. It is thus to be expected, that the uncertainties of the collector parameters gained by a quasi-dynamic test are higher than those from the steady-state test. In this paper we evaluate the collector parameters and their uncertainties for a covered collector using both the SST, and QDT test methods. As basis for this comparison, we apply a large data set from 2 months of operation under quasi-dynamic conditions. This set is then separated into various single data sets which either fulfill the conditions for a complete steady-state or a complete quasi-dynamic test. For the quasi-dynamic test various sets could be identified. For each of these tests, the parameters and their uncertainties are calculated. This allows for the comparison of both, the model coefficients and their uncertainties. It is tested whether the coefficients extracted from each of the ‘quasi-dynamic sets’ are in coherence or stable within a 95% confidence by using statistical procedures.