Improved Modeling for Calculating Instantaneous Efficiency of Flat-Plate Solar Collector

[+] Author and Article Information
Oussama Ibrahim

Faculty of Engineering, Lebanese University, Beirut, Lebanon

Farouk Fardoun

University Institute of Technology, Department GIM, Lebanese University, Saida, Lebanon

Rafic Younes

Faculty of Engineering, Lebanese University, Beirut, Lebanon

Mohamad Ibrahim

Univ Grenoble Alpes, CEA, LITEN, Department of Solar Technologies, INES, F-38000 Grenoble, France

1Corresponding author.

ASME doi:10.1115/1.4038827 History: Received February 07, 2017; Revised November 07, 2017


The performance of a flat-plate solar collector is usually investigated by its efficiency. This efficiency is normally defined on a steady-state basis, which makes it difficult to correctly track the instantaneous performance of the collector in various case-studies. Accordingly, this paper proposes an improved definition of instantaneous efficiency of a flat-plate solar collector used as a part of a solar water heating system. Using a pre-developed model by the authors for such a system, the proposed efficiency-definition is examined and compared with the conventional one for a specific case study. Results show that the improved definition of efficiency records reasonable values, i.e. no over-range values are observed contrast to the case of conventional efficiency-definition. Furthermore, this suggested efficiency approximately coincides with the conventional one at a wide range of time, as long as the system is operating in the so-called trans-steady state phase or when the system is off-operational provided that the instantaneous rate of heat stored in heat transfer fluid is less than or equal to zero. As a result, the improved efficiency-definition yields more realistic results in reflecting the performance of a flat-plate collector in an active solar water heating system and is recommended to be used.

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