EXPERIMENTS WITH A FLAT-PLATE SOLAR WATER HEATING SYSTEM IN THERMOSYPHONIC FLOW

A typical Israeli water heating system in thermosyphonic-flow was tested. The system consisted of two flat plate collectors painted matt black connected in parallel and a 140 l. storage tank. Total surface area of the collectors, employing the parallel flow pattern, was about 3 m2 and they were tilted about 35° relative to the horizon. All collector pipes and connecting tubes were made of galvanized steel. The underside collector plate, collector tubes and storage tank were equipped with thermo-couples. A specially designed flow meter was used to measure water flow rate. Results show relatively linear temperature distributions both along the collectors and in the storage tank when no water consumption was allowed. Water flow rate was found to essentially follow solar radiation and reached a maximum of about 950 cm3/min. This value was found to be about 33 per cent smaller than the one predicted by an analytical model developed by the authors. It was also observed that shutting the system off during the afternoon hours, when losses to the environment are enhanced, might increase system efficiency. © 1979.