Analytical and experimental analysis of procedures for testing solar domestic hot-water systems. NBS Building Science Series 140

Abstract

A repeatable test method independent of outdoor environmental conditions and laboratory geographical location is required in order to provide a means by which solar domestic hot water systems may be rated and compared. Three experimental techniques which allow the net thermal output of an irradiated solar collector array to be reproduced indoors without the use of a solar simulator are investigated. These techniques include use of an electric heat source only, use of a nonirradiated collector array in series with an electric heat source, and the use of electric strip heaters which are attached to the back of nonirradiated absorber plates. Expressions are developed to compute the input power required for each experimental technique. Solar collectors connected in parallel and series combinations are considered. All three test techniques were shown to reproduce the outdoor daily collector array thermal output within four percent. Two of the techniques allow the actions of the circulator controller for an outdoor irradiated system to be duplicated indoors. One technique applies to solar hot water systems which operate on the thermosyphon principle. Experiments conducted to determine the effect of storage tank temperature stratification on system performance for a single-tank direct solar hot water system are described.more » Several return tube designs were fabricated and tested to determine the influence of thermal stratification on system performance. An analytical model for a single-tank direct hot water system is developed. The model is used to support parametric studies for the thermal performance characteristics which result from the use of each test method to duplicate the net theral output of an irradiated array. The model is also used to assess thermal performance differences which occur due to indoor versus outdoor environmental conditions.« less