Sky Temperature Estimation by Three Metallic Plates Method

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Nuttapol Limjeerajarus
Apinya Aksornkij
Sawanya Suwannawong
Sivanappan Kumar


Sky temperature (Tsky) is an important parameter used in the design of solar collectors and nocturnal cooling systems. Thus, correct estimation of the Tsky is essential. In this study, a novel three-metallic-plate (3MP) method has been proposed for the Tsky estimation in which a principle of different heat exchange rates between each metallic plate and the sky dome has been used. The 3MP method uses three aluminium plates coated with various coating materials, which have different absorptivities. By measuring ambient temperature, absorptivities and plate temperatures of each plate and then taking these parameters into account in energy balance equation, the Tsky can be estimated. The 3MP experimental results were used to develop a correlation of Tsky, which were compared with those obtained using pyrgeometer and correlations proposed in previous studies. The results showed that the correlation developed based on the 3MP method can satisfactorily predict the Tsky. Therefore, the 3MP method can be a useful alternative of the Tsky estimation, which has advantages of simplicity and less monetary requirement.


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