A review of low-flow, stratified-tank solar water heating systems

Researchers have discovered that by using low collector flow rates (roughly one-seventh of those that have been generally used) and by taking measures to ensure the water in the storage tank remains stratified, the energy delivered by a forced-flow solar system can be increased substantially. In addition, the lower collector flow rates permit substantial savings in system cost, mainly through reduction in plumbing costs. This paper reviews the state of the art in this highly promising change in approach. Items discussed include physical reasons for the predicted performance improvement, savings in system cost, current knowledge in tank stratification, methods of analyzing and computer-simulating the systems, and finally, full-scale system experiments.