Why is the surface window BSDF beam direction number output from energyplus zero ?

[a200626190111]

Hi,everyone

I used LBNL window to generate a BSDF idf and import the BSDF idf to EnergyPlus.In order to output the hourly incident direction number,I set up the output variable "BSDF Beam Direction Number" in EnergyPlus.But output Surface Window BSDF Beam Direction Number was 0 at all hours,Which is why?

Below is the link for IDF and weather file:

https://drive.google.com/drive/folders/1Osoy8KMgMQbcgl7SU8Ulr-0cUOQ95_0d