Three Experimental Techniques to Duplicate the Net Thermal Output of an Irradiated Collector Array

A relevant and repeatable test method is required to provide a means for rating solar domestic hot water systems. The test method should be independent of the geographical location of the laboratory and the prevailing outdoor environment. Three experimental techniques which reproduce the net thermal output of a normally irradiated solar collector without the use of a solar simulator are investigated. These techniques include the use of an in-line electrical heat source only, use of a nonirradiated collector array in series with a heat source, and the use of electrical strip heaters attached to the back of nonirradiated absorber plates. Two single-tank direct solar domestic hot water systems have been fabricated at the National Bureau of Standards to validate each experimental technique. The solar collector array of one system is subjected to outdoor meteorological conditions. The second system, used to validate the experimental techniques, is located entirely indoors. Daily tests of the solar domestic hot water system with the irradiated collector array were subsequently repeated for the laboratory system using the three experimental techniques. Based on results from several nearly clear and intermittently cloudy days, all three simulation techniques reproduce the net thermal output of the normally irradiated collector array within 4 percent. Pump controller operation can be closely reproduced using two of the techniques. Advantages and limitations of each method are discussed.