Long-term performances prediction of an evacuated tube solar water heating system used for single-family households under typical Nord-African climate (Tunisia)

• We study the performance of an evacuated tube collector system by TRNSYS program.
• A comparison between plate–plat collector and evacuated tube collector system is done.
• The solar fraction of the flat–plate and the evacuated tube collectors is 68% and 84%.
• An economic comparison was also given.

This paper presents a year round energy performance monitoring results of a new type of domestic solar water heating system (DSWH) based on evacuated tube collector (ETC) recently commercialized in Tunisia. This investigation is performed according to two-folded approaches. Firstly, a complete model is formulated taking into account various modes of heat transfer in the DSWH by using TRNSYS simulation program. To validate the TRNSYS model, experimental tests under local weather conditions were performed for 6 days spread over 2 months (November and July 2010). Predicted results were compared to the measurements in order to determine the accuracy of the simulation program. The long-term system performance was then evaluated by means of the Typical Meteorological Year (TMY) data relative to Borj Cedria, Tunisia. Results showed that for an annual total solar insolation of 5489.3 MJ/m2, a total of 4653.13 MJ/m2 were collected by the 3.4 m2 ETC. For 1047.8 MJ/m2 of auxiliary energy supplied to the ETC DSWH system the average solar fraction was 84.4%. An energy performances comparison on yearly basis between the most commercialized flat-plate collector (FPC) DSWH system in Tunisia and ETC DSWH system is also presented in this paper. Results show that the annual average solar fraction of the FPC DSWH systems is lesser (68%) than that of ETC DSWH systems (84%) respectively. It is also found that ETC generated about 9% more energy than the FPC. An economic appraisal was also performed to select the most cost saving between the two DSWH systems.