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Modeling thermal stratification

asked 2018-10-25 12:12:58 -0500

Philhoward gravatar image

updated 2018-10-30 16:26:08 -0500

I am trying to model thermal stratification in a small building with no forced air. Is it possible to do this using the 3 node displacement ventilation measure in openstudio? I uploaded this measure into the model but can't seem to figure out how to get the three different node temperatures in the outputs. Any help is appreciated!

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answered 2018-10-25 13:06:44 -0500

If you are referring to the Change Overhead Ventilation to Displacement Ventilation measure on the BCL, this measure will add a RoomAirSetting:ThreeNodeDisplacementVentilation EnergyPlus object designed for representing a low velocity floor-level displacement ventilation air distribution system. This isn't your exact case of no forced air, so use it with some caution.

Because this measure "injects" this EnergyPlus object into your translated EnergyPlus file from OpenStudio, you won't see its related Output Variables in OpenStudio. However, you can add these using the Add Output Variable measure from the BCL. Here are some Room Air Model variable names that you may be interested in:

You'll need to apply this measure for each output variable that you want to report. After applying all the measures, save your Openstudio model, run a new simulation, and you should see the new output variables appear in the generated CSV file from EnergyPlus. If your OpenStudio file is named My Model.osm, you can find this CSV file in the folder My Model / run starting in the same folder where My Model.osm is saved.

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The names of the node outputs are exactly what I was missing! Thanks! I realize that the displacement ventilation measure isn't at all what I'm modeling, but it is the only way I found to model thermal stratification. Is there another way to model this that you know of? Thanks

Philhoward gravatar imagePhilhoward ( 2018-10-25 13:38:54 -0500 )edit

If you truly want to model thermal stratification, you will need to first simulate your zone in a CFD (computational fluid dynamics) tool outside of EnergyPlus -- EnergyPlus has no CFD capability. This will calculate the air temperature distribution within your zone. Then, you could use one of the Room Air Model objects in your EnergyPlus model to apply the same temperature distribution calculated by the CFD simulation. The workflow would be similar to the paper referenced in this post.

Aaron Boranian gravatar imageAaron Boranian ( 2018-10-25 14:12:49 -0500 )edit

Thanks for the response! Is it possible to define the air flow rate for the displacement ventilation? I looked for a place in the model to define this, but was unsuccessful. I assume that even though I don't have a ventilation system, that there is air flow from this measure, due to the change in my models building energy use. Thanks!

Philhoward gravatar imagePhilhoward ( 2018-11-01 11:33:09 -0500 )edit

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Asked: 2018-10-25 12:12:58 -0500

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Last updated: Oct 25 '18