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If you are defining a window assembly in EnergyPlus, then you have the following options:

1. Use the WindowMaterial:SimpleGlazingSystem object to define parameters for the entire window assembly.

2. Use objects to define individual layers of the assembly (i.e. WindowMaterial:Glazing object for each glass pane)

3. Use the Construction:WindowDataFile object to read an external file generated by LBNL's WINDOW program that analyzes window performance.

If you want to simulate embedded phase change material (PCM) within a window, then you would normally use the MaterialProperty:PhaseChange object to define how the enthalpy and conductivity of the PCM changes for different temperatures. However, EnergyPlus treats PCM as an opaque material layer, and these cannot be assigned to window assemblies. So, you will have to find a workaround using the existing input fields of the three methods above.

1. The WindowMaterial:SimpleGlazingSystem object doesn't have inputs for enthalpy or conductivity, so that won't work.

2. The WindowMaterial:Glazing object has an input field for the conductivity of the glass pane, but not for enthalpy of the glass pane.

3. I'm not sure if LBNL's WINDOW program will account for variable conductivity and/or enthalpy (I haven't used it in a long time).

As a workaround with the method #2, you can try the following process:

• Create multiple WindowMaterial:Glazing objects to represent the different conductivity states or values that you want to analyze.
• Define a Construction object to represent the window assembly for each conductivity state or value that you defined as WindowMaterial:Glazing objects in the previous step.
• Use the Energy Management System (EMS) feature of EnergyPlus to define control logic when you want to apply each window assembly. There is an example of using EMS to switch window assembly construction for thermochromic technology.

Once again, this will only handle the variable conductivity related to PCM. To handle the variable enthalpy of the PCM, you could use EMS to change the amount of "free" heating or cooling provided to the zone from an OtherEquipment object. This isn't quite correct because the variable enthalpy affects the surface where the PCM is embedded, but it's better than not accounting for variable enthalpy at all.