Transient test methods for flat-plate collectors: review and experimental evaluation

Abstract This communication presents a review of the literature on the test methods of flat-plate solar collectors under varying environmental conditions. The methods are classified into different groups based on their common features. The methods are examined critically from the point of view of their: (a)experimental procedures, (b)echniques of parameter identification and (c)output results. Four test procedures have been evaluated experimentally in detail. The results from different tests are compared with each other and with the steady state values based on the ASHRAE 93-86 standard. The review reveals that test procedures based on multi-node models may not be implemented accurately in experimentation. They require impractical measurements or lead to complicated equations for estimation of parameters. A few one-node models include inconvenient test runs or confusing data reduction techniques. The results of the experimental investigation indicate that Saunier's method yields arameters close to those obtained on the basis of the ASHRAE standard. However, the results are greatly affected by measurement errors and propagation of error in various test stages. Exell's method eliminates the inconvenient tests of Saunier's method, but includes a long chain of experiments and does not provide a good estimate of collector characteristics. Rogers' method yields a good estimate of optical efficiency, but underpredicts the heat loss term; it also involves a large amount of computation. The filter method leads to a good estimate of the heat loss term, but it overpredicts the optical efficiency. In addition, precise control of the flow rate and inlet temperature is essential in the last two methods.