Refraction of Light in EnergyPlus

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For questions like this about how EnergyPlus performs calculations, you want to review the Engineering Reference documentation. There is an entire section about Window Calculations, and the index of refraction, $n$, appears in multiple places:

• Conversion from Glass Optical Properties Specified as Index of Refraction and Transmittance at Normal Incidence: How $n$ is used with spectral (visible light) or solar transmittance to calculate spectral or solar reflectance
• Angular Properties for Uncoated Glass: How $n$ is used to calculate the change in transmittance and reflectance at different incidence angles

You can also read another Unmet Hours post for more information.

SUMMARY: Yes, EnergyPlus accounts for index of refraction of light and solar passing through windows.

To see the incidence angle as an output variable, your best option is likely the Surface Outside Face Beam Solar Incident Angle Cosine Value. This is from the surface object defining the fenestration (FenestrationSurface:Detailed, e.g.).

This is only for the outside face of the window -- there isn't a similar output variable for the incidence angle at the inside face of the window. However, incidence angles will only change for different materials or mediums due to their different index of refraction (air vs. glass, for example). Therefore, the incidence angle for light/solar passing through air at the outside face of the window will eventually be the same incidence angle for light/solar passing through air at the inside face of the window after transmitting through all glass layers. See image below taken from here), where $\theta_{i1} = \theta_{r2}$.