This paper presents an experimental comparison of two common heat exchanger configurations used in residential-sized solar water heating systems to evaluate the relative merits and effects of heat exchanger placement (in-tank immersed coil versus external thermosyphon heat exchanger) on storage tank temperature profiles. Experiments were conducted on a specialized test apparatus that allowed controlled charge sequences to be studied for the two configurations considered. The results of this study provide a significant insight into the operation of indirect solar systems configured with immersed coil, or external, heat exchangers and their effect on tank stratification levels. Test results were evaluated on both a First and Second Law Thermodynamic basis, illustrating differences in temperature profiles, energy and exergy levels occurring after identical charge sequences. Results of these tests indicate that, for the configurations studied, higher tank temperatures, stratification and exergy levels were achieved earlier in the charge sequence with the external thermosyphon heat exchanger than with the immersed coil heat exchanger. In addition, it was observed that charging of a partially stratified storage with an immersed coil can result in tank mixing, resulting in a reduction in the temperature and exergy level of the stratification layer.

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Conference 30th ISES Biennial Solar World Congress 2011, SWC 2011
Citation
Harrison, S.J. (Stephen J.), & Cruickshank, C. (2011). Effects of heat exchanger configuration on solar domestic hot water system performance. In 30th ISES Biennial Solar World Congress 2011, SWC 2011 (pp. 3151–3162).