Determination of sky models from ISO CIE 15469- 2004 standard using climate files

Abstract

Most natural daylight simulation programs currently use the Perez Model, which employs climatic data files to determine a set of eight Luminance distribution models characterizing representative models of skies between entirely cloudy and entirely clear. Generally, these simulators also use the ray-tracing method in their simulations, mostly based on the established Radiance algorithms. Since 2004, ISO 15469-2004 (E) -CIE S 011-E 2003 Standard has established 15 Sky Models, similar to the Perez Model but with a distinct formulation. These models were subsequently given calculation treatment in articles to support their specific determination using climatic data. In this work, a new method is presented, based on the mentioned articles, using climatic data to determine, in a set of possible models (the differentiation between models is not unequivocal), which Standard Sky Model is more adequate to the original data. This study was developed using in calculations the radiosity method, although other methods also apply. The calculations tested files from various locations in Brazil and other countries, such as France, Japan, and the USA, reaching results within a very satisfactory approximation range, with average divergences mostly below about 10%, thus demonstrating the consistency of the method.