Proprietary evacuated tube solar water heaters have superior thermal performance in Northern Maritime climates compared with proprietary flat plate solar water heaters. Typically delivering 5-15% more thermal energy per annum, this is, however, achieved with higher capital costs. The adoption of thermosyphon fluid circulation compared with forced circulation systems allows the capital cost of solar water heating systems to be reduced, reliability increased and similar levels of performance to be achieved, for well designed systems. The thermal performance of an evacuated tube solar water heater system utilising thermosyphon fluid circulation subjected to Northern Maritime climatic conditions at the University of Ulster was monitored from the 23rd of September to 21st of November 2006. Measurements including collector outlet temperatures, mean bulk tank temperatures, ambient temperatures, and incident solar radiation levels were used to determine diurnal efficiency. The manifold of an evacuated tube solar water heater was inclined at 1˚: the manifold outlet being higher than the inlet. During the monitoring period it appeared that thermosyphon flow did not always occur in the direction expected. It was deduced that flow reversal had occurred when the collector inlet temperature was greater than that of the outlet. Comparison of the calculated diurnal efficiency for the days when flow reversal occurred with those when it did not indicated that flow reversal reduced the mean calculated diurnal efficiency by approximately 13%.
|Title of host publication||Heat transfer in components and systems for sustainable energy technologies|
|Place of Publication||grenoble france|
|Publication status||Published - 20 Apr 2007|
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- solar energy