A daylight criterion on solar controls for comparing sky radiance models

Abstract

The obstruction of solar radiation by solar controls must be balanced with the required daylight contribution. Solar controls are characterized by the percentage of non-obstructed external radiance. The estimation of this radiance, particularly its diffuse component, depends on the sky radiance distribution used. In this work, we have compared three models (isotropic, CIE clear sky and Perez) before deciding which one is the most suitable for calculating natural light without forgetting the aspect of energy. The incident energy on an aperture where solar control is installed and its daily factor (DF) are the two parameters that have been adopted to analyze the three models. The energy allows us to compare the models and the DF allows us to discuss the weight of each part of the sky dome for each model.

It is deduced that the isotropic model is not suitable for calculating the natural light available in the presence of solar control. The small differences observed between the results obtained with the other two models justify the advantage of using Perez's model in calculations of natural illumination due to its simple formulation.