I am developing a Python thermal simulation for a vehicle cabin and I'm struggling with the radiation balance equation when applying a specific window film layer.
I am using the technical specifications of NTECH (a Korean-made sputtered film) which claims an Infrared Rejection (IRR) of $99\%$ and a Visible Light Transmission (VLT) of $70\%$.
When I plug these values into my current Stefan-Boltzmann based model:
$$Q_{net} = \epsilon \sigma (T_s^4 - T_{sur}^4)$$
The interior temperature curve in my simulation is still significantly higher than the real-world test data provided by the manufacturer.
Does the sputtering technology used in NTECH films require a specific complex refractive index ($n, k$) adjustment in the Fresnel equations, or is a simple attenuation coefficient enough?
How should I weight the IRR vs. UVR ($99.9\%$) in the solar heat gain coefficient (SHGC) calculation to match NTECH's reported Total Solar Energy Rejection (TSER)?
I have already tried using the basic pvlib library for solar angles, but I suspect my absorption/reflection ratio for the metallic sputtered layers is incorrect. Any insights on the optical physics of these specific ceramic films for simulation purposes?