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

Abstract

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 6days spread over 2months (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 5489.3MJ/m2, a total of 4653.13MJ/m2 were collected by the 3.4m2 ETC. For 1047.8MJ/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.