Question-and-Answer Resource for the Building Energy Modeling Community
 | 1 | initial version |
Why do you need to find sky clearness? Normally weather data (ddy file) includes sky clearness. If not, normally 0 is used for WinterDesignDay and 1 is used for SummerDesignDay as a conservative side.
I/O Reference describes under what circumstance sky clearness can exceed 1. "1.0 represents a clear sky at sea level. Values greater than 1.0 may be used for high altitude locations."
Solar radiation increases with altitude due to smaller optical depth of the atmosphere at higher altitudes.
