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International Journal of Renewable Energy Technology Research (IJRETR) ISSN: 2325-3924 (Online)
Table of Contents Articles Authors: Samer Alsadi and Yasser Fathi Nassar Pages: 1-16 Abstract In Arabic territories, the ASHRAE clear sky model is commonly used as a basic tool for solar radiation estimation. Unfortunately, this model was developed for the atmospheric condition in the USA, which was quite different from weather conditions of the Arabic territories. The purpose of this study was to revise all parameters of the ASHRAE model under the atmospheric conditions of Arabic countries in an attempt to improve the accuracy of the model. The solar-radiation over horizontal surface calculated by the ASHRAE clear-sky model is compared with measurements form (Brack-Libya, Tulkarm-Palestine and Riyadh- Saudi Arabia) cities in order to test the validity of the ASHRAE clear-sky model parameters (A, B and C).The revised model is tested against statistical analysis based on RMSE, MBE and t-stat. the results showed that the revised model can be a good estimator for the prediction of global solar radiation in Arabic countries with an acceptable agreement to the measured data from meteorological record stations. That performance is a more accurate prediction than those throughout the previous studies. This model presented the unique alternative approach for solar radiation prediction in regard to the locations where there is no availability of some input data for other models. Instantaneous, daily, monthly and yearly solar-radiation on various surfaces such as building walls and flat-plate solar collectors can then be conveniently calculated using the adjusted model for different orientations and inclination angles. The model also allows the beam, diffuse and ground-reflected solar-radiation components to be determined separately. Keywords: Clear sky model, ASHRAE model, solar radiation data of Palestine, solar radiation data of Libya, solar radiation data of Saudi Arabia
Optimization of flat-plate solar collectors used in thermosyphon solar water heater Authors: Koholé Yemeli Wenceslas and Tchuen Ghislain Abstract In this paper, thermodynamic optimization based on exergy concept is developed to determine the optimal combination of values for the constructional parameters. This maximizes the exergetic efficiency of three flat-plate solar collectors commonly used in thermosyphon solar water heaters (SWH). The effect of some design parameters on the performance of a flat-plate collector has also been investigated. It has been observed that, the optimal combination of values that maximizes the exergetic efficiency for the three models are the same, with a slight difference in the maximum exergetic efficiencies. After studying a more practical situation, it has been realized that, a distance of ten centimeters between the riser tubes lead to a more cost-effective solution for designers. A change in the distance between the absorber plate and the glass cover from 0.001 to 0.03 m indicates a strong influence of the distance between the absorber plate and glass cover on the heater performance. It has also been observed that, increasing the insulator thickness to approximately 0.05 m leads to an increase in the performance of the system. The results also show the possibility to reach higher exergy efficiency with lower absorber area and consequently lower price. Keywords: Absorber plate, Exergy, Flat-plate, Genetic algorithm, Water heater.
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