Grey model of direct solar radiation intensity on the horizontal plane for cooling loads calculation

According to the tenets of Grey System Theory, this paper analyzes the stochastic characteristics of the attenuation rate of solar radiation intensity, and then presents a grey model for direct solar radiation on the horizontal plane on sunny days. By combining the definitive physical model with the grey parameter, this grey model describes the attenuation pattern of solar radiation intensity more comprehensively and more reasonably. Based on the principle of message assembly, the authors find out two envelope curves which describe the maximum and minimum limits of the collective influence of all stochastic factors, and estimate the optimum varying interval of a grey parameter in the model with the help of the least square method. Finally, a concept of a grey degree is proposed to represent the degree of confidence for the optimum value of a grey parameter, thus providing a reasonable theoretical base for calculating the intensity of solar radiation on sunny days.