Optimal slope angle selection of an evacuated tube collector for domestic solar water heating

Rigardt Alfred Maarten Coetzee, Aggrey Mwesigye, Zhongjie Huan

Research output: Contribution to specialist publicationArticle

5 Scopus citations


A pressurised system utilising evacuated tube collectors with internal heat pipes was investigated for the production of hot service-water for domestic use during all seasons in Pretoria, South Africa. The investigation focused on the prediction of seasonal hourly performance trends and the maximum thermal performance at the optimal slope angle. This study was accomplished by developing the system's theoretical performance model which was solved numerically using Engineering Equation Solver. Results show the thermal performance of the system during the sequential seasons at different slope angles. Optimal performance parameters that influence the collector overall performance, depending on the water consumption of the occupants, were obtained and presented. In summer, a 25° slope angle produced the highest useful heat rate and in winter, a slope angle of 40° produced the highest. Lastly, a 20-tube collector system operated maximally in September, reaching an outlet temperature of 103.98 °C and yielding a useful heat rate of 1 919.85 W.

Original languageEnglish (US)
Number of pages16
Specialist publicationJournal of Energy in Southern Africa
StatePublished - 2017
Externally publishedYes

Bibliographical note

Funding Information:
The support received from the Tshwane University of Technology and the University of the Witwatersrand is acknowledged. The support received from the National Research Foundation is also acknowledged. Special thanks to the South African Weather Service for provid-ing data used in this investigation.


  • Dual tank system
  • Heat pipes
  • Simple system model
  • Slope angle
  • solar thermal


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