How to model electrochromic glazings in radiance?

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The simplest method is to generate a Radiance material description for state of the electrochromic device, and run a simulation with each. If you need to do an annual simulation you can run the daylight coefficient method for each state and blend the results hour by hour in post processing.

A more complicated but perhaps elegant method is to generate a BSDF file for each state and use the three phase method. With the three phase method you can use dctimestep to change the glazing properties for each hour. The three-phase method is intended for dynamic and/or optically complex facades.

To generate the material definitions, the start in LBNL Window. Create a glazing system with your electrochormic device in the outer pane and a low-e coated pane (Guardian Neutral 78/65 pairs well with Halio) or a clear pane (with View or Sage). Create a glazing system for each tint state. Then export a "radiance file" file for the glazing systems from window. In Radiance, you need to run the script optics2rad to correct the material description. Then you can use the script output as materials in your Radiance model.

To generate BSDF files for the three-phase method, section 3.2.1 of the now deprecated three-phase tutorial (https://radiance-online.org/learning/...) is still the best resource. However to learn how to use the three-phase method, the more recent tutorial on matrix based methods is your best resource since many of the Radiance programs have changed: https://radiance-online.org/learning/....