Fenestration peak solar heat gain: A review of the cloudless day condition as conservative hypothesis

Abstract

Peak solar heat gain through fenestration, particularly for clear and cloudy day conditions, was estimated, using an approach based on the ASHRAE methodology and considering the correlation between hourly clearness index kT and diffuse ratio of the total radiation. Hourly SHGCLEAR and SHGCLOUDY values for surfaces facing the basic cardinal orientations and the horizontal surface, at different latitudes, on the 21st day of each month, have been computed and compared. Results show that in many cases solar heat gain for cloudy day may exceed that for clear day. For wall exposures near the North the clear day condition could not be the most conservative condition for the peak SHG evaluation.