A Classification of Real Sky Conditions for Yongin, Korea

Abstract

Information on sky condition classification is important to the energy-efficient and sustainable building designs for predicting the energy consumption and daylight performance. Sky conditions are commonly classified into overcast, partly cloudy, and clear sky. IESNA’s Sky Ratio (SR), Perez’s Clearness Index (CI), Li’s Clearness Index (Kt) are representative sky conditions classification. However, reliable and accurate daylight climatic data are lacking in Korea. Thus, this paper presents a classification of real sky condition for Yongin, Korea from data recorded during a period of one year at the KHU station. For the research, illuminance and irradiance data were obtained from 1st February 2011 to 31st January 2012. Hourly frequency of sky conditions occurrence and hourly global horizontal illuminance were analysed according to sky conditions. It was found that sky conditions in Yongin, Korea are classified, respectively, as clear and overcast skies 34% and 17% of the time in Yongin, Korea. These findings indicate that sky condition classification and illuminance information gathered at KHU could be applied for various daylight design applications and energy-efficient building design in Yongin, Korea.