THERMAL IMPROVEMENT OF SOLAR HOT WATER

Abstract

This study includes a comparison between the performances of two locallyfabricated similar flat plate solar collectors. One of these collectors is a new design ofaccelerated absorber, its risers are of converging ducts (the exit area is half that at theentrance). The other collector is of conventional absorber (its risers have the same crosssectional area along its length). Each collector is the major part of an indirectthermosyphon circulation solar hot water system facing the south with a fixed tilt angleof 33.3 o from the horizontal. A side by side experiments are conducted for three months 1,2,&3 of 2009 for different water withdrawal profiles, continuous, interrupted and no load, also forhorizontal and vertical storage tank orientations. Two types of storage tanks areinvestigated (two concentric cylinders and helically coiled tube in cylinder). Results show that a considerable enhancement of thermal performanceapproximately (60%) of absorbed heat (useful gain) at solar noon is obtained for thenew design in comparison with the conventional type. The instantaneous efficiency was31.5% for the accelerated absorbed flat plate at solar noon, while that of conventionalabsorber was (16.5%). The longitudinal water temperature variations in the risers ofaccelerated absorber were larger than that belong to the conventional absorber. Thestratification in the storage tank is considerably improved for the solar hot water systemwith the new absorber design in which the maximum temperature indicated was 50 C(vertical storage tank) while that for conventional absorber was 37 oC. The stratificationobtained for coiled tube in cylinder storage tank indicates a good thermal performancewith less space requirements. Also the circulation rate in the accelerated absorber washigher when it is connected to coiled tube than that when it is connected to theconcentric cylinders.o