INDICES TO ESTIMATE SKY RADIANCE DISTRIBUTION : A study on modeling sky radiance distribution Part 1

In effective use of solar energy and the heating and cooling load calculation of buildings for energy conservation, the actual state meteorological data is indispensable. The sky radiance distribution has been expediently assumed to be uniform distribution in the heating and cooling load calculation of buildings because there was no suitable sky radiance distribution model. It is necessary to propose sky radiance distribution model, which can corresoond to all sky conditions from clear sky to overcast sky. A suitable index is necessary to presume sky radiance distribution because sky radiance distribution is not measured in ordinary weather observations. In this paper, normalized global irradiance and cloudless index are defined based on measured data as indices to classify sky radiance distributions. The relationship between both indices and sky radiance distributions was examined, and the validity as the indices for the presumption of sky radiance distributions was confirmed.