Study of the Impact of Automatic Backflush on Direct SDHW Thermosyphon Systems
Abstract
Thermosyphon solar water heaters are often deployed in regions where freezing ambient conditions do not occur, allowing potable water from the storage tank to be directly circulated through the solar collectors. In many regions “hard water” conditions exist where dissolved minerals can deposit on hot surfaces within the solar collector’s flow tubes, restricting the flow of water and resulting in increasing collector temperatures. A recent development aims to alleviate this condition by introducing a novel flow configuration and valving system that reverses the flow of cold “mains” water through the solar collectors each time hot water is drawn from the system. This flushes the collector, and the regular introduction of cooler “mains” water significantly reduces the potential of hardwater scaling in the solar collectors. This study investigates the effect of this flow reversal on the energy delivered to the end user through a side-by-side comparison of two thermosyphon solar systems; one with the backflush feature and one without.