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# Has anyone gotten a two-stage Transcritical CO2 system to function in OS?

I have been unable to get a two-stage Transcritical CO2 system to even open up in the OS app. My approach has been to create the standard refrigeration system objects in the OS app, with compressors and condenser objects. Then, manually edit the .osm text file to replace the standard refrigeration objects with transcritical objects, replace the condenser with a gas cooler object, and add transcritical compressor coefficients for the high pressure compressors. After making these changes, I have not been able to reopen the model file in the OS app. The error continues to say either field 3 or field 4 of the transcritical system has an incorrect data type:

The collection is INVALID at strictness level 'Draft', because of the errors: Field level data error of type DataType . Error is in an object of type 'OS:Refrigeration:TranscriticalSystem', named 'Rack A1B1 TransRefrigSys', in field 4. Additional information about the error type: field-level data is of an incorrect type.

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Like @Kyle Benne mentioned, two-stage transcritical systems are supported but you have to be careful about editing the osm manually.

I bet you are adding the Refrigeration:TranscriticalSystem like it is in the EnergyPlus IDD, however, the OpenStudio Model IDD is subtlety different for this object. Some of the fields can be inferred during Forward Translation from OSM -> IDF so they are not in the OSM.

Since you mentioned it comes with an error in field 3 or 4, I bet you have the field 'System Type' as 'TwoStage', which is A2 in the EnergyPlus IDD. This is one of the fields that is inferred during forward translation thus is not in the OSM IDD. Another difference between the OSM IDD and E+ IDD is the objects and terminology used for the Refrigerated CaseAndWalkInLists.

Your best bet to manually construct the OSM is to look at the OSM IDD and make sure you conform to its specifications since this is what is used when loading an OSM.

Look here for OS:Refrigeration:TranscriticalSystem in OpenStudio IDD

But I would really try to use either the ruby API directly or a measure to construct this type of system until it is supported in the GUI.

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I got it to work after removing the 'TwoStage' field. Thank you! I would prefer to do all of this with measures; however, I still have not been able to wrap my head around the complete process of developing a measure. I have gone through the measure writing guide (which all makes sense), but once I get into the SDK documentation and try to figure out how to write my own measure I get lost. I appreciate the feedback!

( 2015-03-27 11:34:48 -0600 )edit

In general it's not recommended to edit the OSM file directly like one might an IDF and the errors you're getting are likely due to OS not supporting the EP objects/fields yet. During an OS simulation the OSM file is translated to the in.idf file located in osm file folder > run > ModelToIDF.

To use EP features that are not yet exposed in OS, write an EnergyPlus Measure which will edit the in.idf file before it's translated to the out.idf file run by EP.

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OpenStudio won't like it if you manually edit the .osm to add functionality that's not currently supported. The best way to add or edit EnergyPlus objects in a model generated with OpenStudio is with an EnergyPlus measure or by manually editing the .idf file that's generated when you run the OpenStudio model. The .idf can usually be found in the project folder -> run -> 4-EnergyPlus-0.

edit: Ok, turns out Transcritical systems are supported in OS. However, I still think editing the .osm by hand is not a good idea. If you aren't able to create/edit the objects using the application interface, I would suggest looking into an OpenStudio measure.

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Transcritical systems are supported in OpenStudio via the API, but they are not exposed in the graphical Application. Eric's answer correct on all points.

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Why does OpenStudio seem so finicky with manually adding osm objects to the .osm file? Is there something obvious that I could be missing? I use generated handles (so as to not randomly create my own handles) and it still seems to not like the addition. Wouldn't a OS measure pretty much do the same thing? I understand the need for a OS measure with more complicated additions, but with refrigeration the objects are not really connected to anything in the same way HVAC is. So, it would seem that just adding the transcritical system object should be pretty simple/straightforward.

( 2015-03-27 09:47:42 -0600 )edit
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It is not impossible to successfully edit an osm file as text, particularly if the relationships between other objects are minimal. But we can't support this. Editing the OpenStudio Model through the API ensures that required relationships and assumptions built into the OpenStudio Model are maintained.

( 2015-03-27 09:54:53 -0600 )edit