Openstudio Solar Model Indicator

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I'm assuming you're talking about the SizingPeriod:DesignDay object, specifically the Solar Model Indicator.

You're seeing no fenestration load because when you switch to ASHRAEClearSky it will look for the Sky Clearness (instead of the two tau values, $\tau_b$ and $\tau_d$). You probably left this field blank, which will default to 0, meaning no solar gains.

Clearness may range from 0.0 to 1.2, where 1.0 represents a clear sky at sea level. Values greater than 1.0 may be used for high altitude locations. Traditionally, one uses 0.0 clearness for Winter Design Days.

Edit:

Considering that the Sky Clearness field isn't exposed in the OpenStudio App, you could do something like this to change all your summer design days (the winter ones are usually already as Clear Sky, with clearness of 0) to Clear Sky with a value of 1.0

model.getDesignDays.each do |dd|
 if dd.dayType == 'SummerDesignDay'
   dd.setSolarModelIndicator("ASHRAEClearSky")
   dd.setSkyClearness(1.0)
 end
end