[Gopal_Åbo]

I have a skylight for roof top modeled with two different materials
1. regular window glass which is opaque for longwave radiation.
2. ZnS glass is 75% (0.75) transparent to the longwave radiation.
I used Discrete Ordinates (DO) Model since it is the only model with 'semi-transparent' and 'non-gray' mode.
I made four bands, 0 – 4, 4 – 8, 8-14, 14-50 µm in Model - Radiation - Number of Bands,
Lets assume that :
Topside window glass and top side ZnS glass are exposed to ambient surroundings at 296 K
bottom side window glass and bottom side ZnS glass are located inside building space at 298 K
Now, I turned on solar calculator,
Input the data such as Latitude, longitude and time and data, (this is fine).
Direct solar irradiation as 660 W/m2
Diffuse solar irradiation as 125 W/m2
Then, I turned on solar BC options for both top side window glass and top side ZnS glass.
Direct and diffuse irradiation values are directly calculated by Ansys Fluent,
I think, Diffuse fraction = Diffuse irradiation/(direct irradiation + diffuse irradiation).
Now, the question is:
For bottom side window glass, for bottom side ZnS glass, I want to set
Direct irradiation = ? Perhaps it is zero in all bands´(1 to 4)
Diffuse irradiations = band 1 to band 4 = (need help here).
Diffuse fraction= band 1 to band 4 = (need help here).
Please find the attached screen shots for better idea.