How to add a "new output" in E+ (idf editor)

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It looks like you are creating the RDD with a "Regular" syntax instead of "IDF" syntax. The text format you've pasted isn't what EnergyPlus requires to define an object (start with object class, end with semicolon ";", etc.). This is likely the cause of your severe error stopping the simulation, which prevents EnergyPlus from generating an updated RDD file.

I would recommend trying to change the Output:VariableDictionary object like below:

Output:VariableDictionary,
  IDF;                                      !- Key Field (Desired RDD Format)

If you save the IDF and run future simulations, you can directly copy Output:Variable lines from the RDD and paste them into the IDF without reformatting. Saving and simulating again will add these new output variables to the ESO and CSV output files.

For the specific Zone Air Terminal Cold Supply Duct Damper Position output variable that you're interested in, EnergyPlus can only generate that if you have the dual duct VAV air terminal object type or dual duct CAV air terminal object type defined in the IDF.