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OA for unitary system

asked 2015-07-31 12:01:19 -0500

Rohini gravatar image

updated 2015-07-31 13:44:21 -0500

Waseem gravatar image

I am using a AirLoopHVAC:UnitarySystem. I cannot figure out if it is getting outside air or not. I cannot see the OA node flow rate or temperature as output - these don't show up in the csv file. Is there something else I can output that will show how the OA mixer is working? Thanks, -Rohini

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@Rohini please edit your question to use existing tags.

MatthewSteen gravatar image MatthewSteen  ( 2015-07-31 12:39:53 -0500 )edit

I can certainly do that if you tell me what exactly does that mean - is there a list of tags somewhere that I should be choosing from? Are you talking about the body of the question or the "upto 5 tags" I am supposed to add?

Rohini gravatar image Rohini  ( 2015-07-31 12:59:25 -0500 )edit

Just noticed that there is a list of tags. Is there a way to enter relevant once in the body of the text easily?

Rohini gravatar image Rohini  ( 2015-07-31 13:07:22 -0500 )edit

Yes, it should display existing ones while you type, although it will also display unused ones. Best to search from the tags page and choose existing ones that are the most used. Our convention is to use a - between words. Thanks!

MatthewSteen gravatar image MatthewSteen  ( 2015-07-31 13:17:36 -0500 )edit

Nothing displays when I type a question.

Rohini gravatar image Rohini  ( 2015-07-31 13:32:40 -0500 )edit

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answered 2015-07-31 14:06:28 -0500

updated 2015-07-31 15:31:51 -0500

The AirLoopHVAC:UnitarySystem object does not contain an outside air system. You need to add an AirLoopHVACOutdoorAirSystem to the AirLoopHVAC structure separately from the unitary. Look at UnitarySystem_DXCoilSystemAuto.idf as an example.

Assuming you have an outdoor air system installed and properly configured, you can verify the operation with one of the following output reports.

Output:Variable,*,Zone Mechanical Ventilation Mass Flow Rate,detailed; !- HVAC Average [kg/s]
Output:Variable,*,Zone Mechanical Ventilation Mass,detailed; !- HVAC Sum [kg]
Output:Variable,*,Zone Mechanical Ventilation Standard Density Volume Flow Rate,detailed; !- HVAC Average [m3/s]
Output:Variable,*,Zone Mechanical Ventilation Standard Density Volume,detailed; !- HVAC Sum [m3]
Output:Variable,*,Zone Mechanical Ventilation Current Density Volume Flow Rate,detailed; !- HVAC Average [m3/s]
Output:Variable,*,Zone Mechanical Ventilation Current Density Volume,detailed; !- HVAC Sum [m3]
Output:Variable,*,Zone Mechanical Ventilation Air Changes per Hour,detailed; !- HVAC Average [ach]

Or the most direct way, by reporting the oa node flow rate directly.

Output:Variable,*,System Node Mass Flow Rate,detailed; !- HVAC Average [kg/s] <-- filling in the oa node name for *
Output:Variable,*,System Node Standard Density Volume Flow Rate,detailed; !- HVAC Average [m3/s]
Output:Variable,*,System Node Current Density Volume Flow Rate,detailed; !- HVAC Average [m3/s]
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I have the AirLoopHVACOutdoorAirSystem and the AirLoopHVAC:UnitarySystem in the branch object. If I look at the temp for the OA (environmental) and mixed node - these are same, so there is OA coming in (at 100%) - it would have been easy if the OA node numbers could be output directly. The output works for the non-unitary HVAC system.

Rohini gravatar image Rohini  ( 2015-07-31 15:09:31 -0500 )edit

I updated the response with some report variables that might be useful to you. You might want to back down the "detailed" frequency to "hourly" if you are going to view these in a spreadsheet.

Kyle Benne gravatar image Kyle Benne  ( 2015-07-31 15:35:52 -0500 )edit

I have been using the - Output:Variable,*,System Node Standard Density Volume Flow Rate,detailed; !- HVAC Average [m3/s] - and the temp for this node. These both don't show up in the output file. I will try the others. Thanks.

Rohini gravatar image Rohini  ( 2015-07-31 15:37:42 -0500 )edit

What file are you looking in? These report variables are output to the eplusout.eso file automatically, and the eplusout.sql file if you ask for it. The readvarseso program can read the eso file and turn it into a csv file. OpenStudio's ResultsViewer Application is good if you want to work with the sql file.

Kyle Benne gravatar image Kyle Benne  ( 2015-07-31 15:59:15 -0500 )edit

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Asked: 2015-07-31 12:01:19 -0500

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Last updated: Jul 31 '15