HI-85-04-3 -- Field Testing of Systems Using Controls to Enhance Thermal Stratification during Solar Collection PDF

A new solar collection strategy, NCS, was proposed by R. L. Cole and F. 0. Bellinger (1982) in a paper entitled "Thermally Stratified Tanks" ¹. Since the proposed strategy was untested, and was radically different from standard practice, an experiment was designed to test and evaluate its merits.

To accomplish the experimental evaluation, side-by-side testing of identical solar DHW systems was performed in the experimental testing station on the campus of Arizona State University. Over the several years that this work was conducted, both pumped-recirculation and antifreeze systems were used.

The NCS called for drastically reduced collector array supply flow rates so that two objectives were met. First, the entire solar storage volume would make only one trip a day to the collector array rather than the usual one trip per hour. Second, the temperature of the solar heated water returned to the storage must be at the minimum temperature required to satisfy the load - typically 130F (540C) in DHW systems.

Based upon experimentation under actual weather conditions with a prescribed load, it was found that the NCS produced a 15-20% improvement in thermal performance over the standard nonstratified operation. This encouraging performance improvement was found to occur on clear and cloudy days alike . In addition to improved performance, the new collection strategy, in some cases, could result in reduced pump size and operating cost and smaller array supply and return piping.

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