Weather data Horizontal Infrared Radiation Intensity

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Hello to all, the Horizontal Infrared Radiation Intensity is used in the EnergyPlus simulation, right? If it is missing, it is calculated from the Opaque Sky Cover. But if I specify neither Horizontal Infrared Radiation Intensity nor Opaque Sky Cover, the simulation runs anyway. What value is assumed for Opaque Sky Cover?

PS: Regarding the additional Software-Tool Elements, is the Input "Infrared Sky Radiation" equal to "Horizontal Infrared Radiation Intensity"?

Thank you for any help! M.