How to add phase change materials properties in openstudio?

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MaterialProperty:PhaseChange and MaterialPropoert:VariableThermalConductivity can help you simulate PCM application in buildings, for a start. They have not been wrapped in OS as of now. I think the best way to do this in OpenStudio is to write an Energyplus script to include these objects in your model. It is also worth noting that the HeatBalanceAlgorithm for these models should be changed to ConductionFiniteDifference for energyplus to simulate PCM performance (the default is CondcutionTransferFunction). In OpenStudio, this can be changed in the Settings tab of the GUI. Hope this helps!