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# Embed PCM in Window Glazing system

I'm using EnergyPlus and I'm trying to embed a Phase Change Material into a glazing system, but I get the following error:

   ** Severe  ** MaterialProperty:PhaseChange: Reference Material is not appropriate type for CondFD properties, material=AIR, must have regular properties (L,Cp,K,D)
**  Fatal  ** GetCondFDInput: Errors found getting ConductionFiniteDifference properties. Program terminates.
...Summary of Errors that led to program termination:
..... Reference severe error count=1
..... Last severe error=MaterialProperty:PhaseChange: Reference Material is not appropriate type for CondFD properties, material=AIR, must have regular properties (L,Cp,K,D)


I found this question and this other question about the same topic, nevertheless they have no answer.

A comment on the last one suggests emailing the author of the first one, but I'm unable to find the e-mail of any user (maybe it is a limitation of my karma as a new user?).

Any feedback on how to achieve this (maybe there is a workaround using another kind of materials or using the Python API?) will be appreciated.

Also, if you could provide me the means to contact the users who has the same problem (e.g. their emails) I would really appreciate it, too.

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@elsa if you click on the name of an Unmet Hours user, then you can view their profile where you will find some of their information, but not their email (only moderators on Unmet Horus can see that).

( 2020-10-04 08:15:39 -0500 )edit

Thanks @Aaron Boranian. Unfortunately, on their profiles I'm only able to see the "member since", "last seen" and "todays unused votes" fields. I think this might be because one requires greater karma in order to see other user's emails.

( 2020-10-04 10:46:28 -0500 )edit

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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:

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.

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Thanks, I'll try this approach! Alternatively, I was considering on compiling EnergyPlus myself adding a class for the a new type of Translucent PCM, which would have both the properties of gases (which are not opaque can be used within windows) and PCM (which have the conductivity and enthalpy I need to consider in my simulation). Nevertheless, I wonder if this is a viable approach and if someone else has already done something like this. Specifically there's a lot of literature abour TIM-PCM which look similar to what I need, but I have not found a TIM-PCM for EnergyPlus.

( 2020-10-04 10:55:29 -0500 )edit

Modifying the EnergyPlus source code to compile your own unique version can be done, but it is not an easy task if you don't have much experience programming in C++. As an alternative, you could add this as a feature request issue on the EnergyPlus Github site where the source code is hosted. That would let the development team know that users want this feature and encourage them to add it to a future public release of EnergyPlus. If you have an urgent need for this project, modifying source code yourself may go faster.

( 2020-10-04 11:43:17 -0500 )edit

Thanks again! I do have some experience in C and other languages of the C family (Java, C#), but before engaging in such a task, I'd like to make sure that the solution isn't already out there. E.g., if there is something as a TIM-PCM material for EnergyPlus, I might use a TIM-PCM wall instead of a PCM embeded glazing and it could work just as well. Is there any place I should check to tell if this already exists?

( 2020-10-04 12:08:45 -0500 )edit

Also, I haven't been able to find documentation about specifically creating new materials in the source code. My first idea would be to create a new class inheriting both from WindowMaterial:Gas and some other material containing MaterialProperty:PhaseChange. Nevertheless, I'm not sure if that would make sense at all for EnergyPlus.

( 2020-10-04 12:11:39 -0500 )edit

Hello. I also encountered this problem. If anyone has a solution, tell me. Placement of phase change material in glass

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