A proprietary heat-pipe Evacuated Tube Solar Water Heater originally designed for collection of solar energy using forced fluid circulation was operated using thermosyphon fluid circulation. The thermal performance of this solar water heating system was monitored from October 2006 to June 2007 at the University of Ulster. The ETSWH was inclined with the expected collector outlet at a higher datum level than the expected collector inlet to provide a hydrostatic pressure differential across the manifold. During the monitoring period it was observed that thermosyphon flow was not always in the expected direction with flow reversal when the collector inlet temperature was greater than that of the outlet. When the evacuated tube solar water heater was inclined at 1˚ reverse fluid flow was observed to occur for 69% of the monitored diurnal periods. Diurnal reverse circulation reduced systemefficiency by degradation of thermal stratification in the hot water storage tank via convective entrainment and mixing.The thermal performance of the ETSWH was monitored continuously from January 2007 to June 2007 with the manifold inclined at 5° from the horizontal. Over this time period it was found that fluid flow reversal arose for 22% of the diurnal periods considered, resulting in a 47% improvement in diurnal storage efficiency compared to when the system had its manifold inclined at 1°. The long term diurnal storage efficiency of the optimised system inclined at 5 ° was measured as 66%.
|Journal||International Journal of Ambient Energy|
|Publication status||Published (in print/issue) - 1 Apr 2010|