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ideal air loads and openstudio

asked 2017-05-12 22:20:04 -0600

Matt Koch gravatar image

updated 2017-05-13 17:01:56 -0600

So, I was perusing the web on the subject, and I am not sure I am interpreting what I found correctly. However, here is my - possibly erroneous - take on it.

1) In order to avoid having to model any HVAC loops, I have to use ideal air loads - yes, no?

2) When using ideal air loads, no outdoor air is being included in the calculations - ever - no matter what is entered under Spaces -> Airflow -> Design Specification Outdoor Air Object Name?

3) Hence, if I do want to investigate outdoor air, I must model my HVAC loops?

I'd appreciate your advice on this.

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answered 2017-05-15 11:31:40 -0600

I made an EnergyPlus measure that loops through each zone and injects the Design Specification Outdoor Air object into the Ideal Loads Air System object. I also made it possible to edit other fields and add reporting variables as a default.

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So, I was trying to use this measure in PAT (1.14.0) just now. However, in "Organize and Edit Measures for Project", the measure has a red exclamation mark, and when clicking on the measure, the three schedule choices are red, just as shown in the above image. I cannot make any selections here, and the out.idf file likewise shown empty entries for these, so I should not have to make any selections, or they should default to empty? Any thoughts? In the meantime, I have written a Scilab script to accomplish what I did manually below, but it would be nice to have a working official measure.

Matt Koch gravatar imageMatt Koch ( 2017-05-15 14:35:04 -0600 )edit

you need to create a Schedule:Ruleset object that is the Availability schedule for your HVAC system. If you want it always on, you can create a default schedule that is always 1. Use Schedule Type OnOff.

mdahlhausen gravatar imagemdahlhausen ( 2017-05-15 15:13:50 -0600 )edit

So, looks like this only works when there are OA specifications of all zones. I have some plenum zones for which I have no OA specification. I suspect that is why the simulation fails with the following error?

"Error: Unable to find design specification outdoor air for zone TZ-FA-PC. Please specify a design specification outdoor air object for the zone, or select None for Outdoor Air Specification."

Matt Koch gravatar imageMatt Koch ( 2017-05-19 11:27:18 -0600 )edit

OK, so I simply commented out the following two lines:

runner.registerError("Unable to find design specification outdoor air for zone #{zone_name}. Please specify a design specification outdoor air object for the zone, or select None for Outdoor Air Specification.")

return false

in the measure.rb file, and now it runs through, and also delivers the same results that I had obtained earlier through my "non-conformist" approach.

Matt Koch gravatar imageMatt Koch ( 2017-05-19 11:42:21 -0600 )edit

The measure is exiting at that error. You can modify the measure to skip the plenum zones (you'd need a way to tell the measure which zones to skip), or alternately, create a plenum space type with zero values in the design specification outdoor air and then have your plenum zones have spaces of that space type.

mdahlhausen gravatar imagemdahlhausen ( 2017-05-19 12:20:15 -0600 )edit
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answered 2017-05-12 22:23:29 -0600

Matt Koch gravatar image

So, I set up a model in SketchUp/OpenStudio and ran it with ideal air loads in OpenStudio/EnergyPlus. If I understand correctly, this does not include outdoor air, even though I specified such in SketchUp/OpenStudio. In reviewing the "eplustbl.htm" file from the "run/nn-EnergyPlus-0" directory, the Outdoor Air Summary indeed shows 0 ach for Mechanical Ventilation (although it shows non-0 ach for Simple Ventilation - not sure what that is).

Then I edited the "out.idf" file from the "run/nn-EnergyPlusPreProcess-0" directory. Towards the end of the file, there is a section entitled "New objects created from ExpandObjects" (not sure what that is). In it are sections entitled ZoneHVAC:IdealLoadsAirSystem for each thermal zone of the model, and within these is a line named "Design Specification Outdoor Air Object Name". Towards the beginning of the same "out.idf" file are sections entitled DesignSpecification:OutdoorAir, and within these is a line named "Name".

So, I copied the name from the "Name" line of the DesignSpecification:OutdoorAir section to right before the comma on the "Design Specification Outdoor Air Object Name" line in the ZoneHVAC:IdealLoadsAirSystem section - correspondingly for each zone. That is a lot of copy and paste and requires some concentration, but it can be done. Then I ran this modified "out.idf" file straight through EnergyPlus, using the following:

cd 2-EnergyPlus-0

C:\Software\OpenStudio\share\openstudio\EnergyPlus-8-6-0\energyplus -w C:\Software\WeatherData\USA_TX_San.Antonio.Intl.AP.722530_TMY3.epw ..\1-EnergyPlusPreProcess-0\out.idf

cd ..

Now the "eplustbl.htm" file from the "run/nn-EnergyPlus-0" directory, shows non-0 ach in the Outdoor Air Summary for Mechanical Ventilation, and still the same non-0 ach for Simple Ventilation as before. The site and source Energy Use Intensity (MJ/m2) has increased as well.

Is this then how one can force Ideal Air Loads to include outdoor air?

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Asked: 2017-05-12 22:20:04 -0600

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Last updated: May 15