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# Zone within a zone

I have thermal zone which is enclosed within another thermal zone. I have attached the picture below. The question is, when I create a zone within a zone the boundary conditions of the inner zone is Outdoor. However, this is a completely inner zone whose walls no contact with the outdoor conditions. You see, the outer zone is maintained at 25 C and inner is maintained at 18 C What should be boundary conditions of the inner zone ?!

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Just curious in this configuration, how is the outer zone floor surface represented in EnergyPlus? Its essentially a rectangle with a hole inside, 8 vertices in total. The surface is not simply connected anymore. How does SketchUp arrange the 8 vertices in a series to represent such a surface?

( 2018-09-05 14:16:07 -0500 )edit

It is just a rectangle, it has no holes in it. Atleast, I have not created any holes in it. However, I am unsure how sketchup exports it.

( 2018-09-06 01:58:50 -0500 )edit

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You will get a severe or fatal error by having a space within a space in OpenStudio. This will create non-convex geometry, and EnergyPlus will have difficulty calculating the zone volume.

I recommend splitting the larger space into two spaces, setting the connecting surface as an air wall, and then assigning them under the same zone in OpenStudio. Your boundary conditions on the interior will be 'Surface' matched to the adjacent surface. The surface matching feature in OpenStudio should do this automatically.

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I believe that just like any other internal wall which divide two zones the condition should be the other side Surface.

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The outside boundary condition for the wall surfaces of the inner zone is the outer zone (or rather the surfaces in the outer zone corresponding to the "other sides" of the inner-zone walls). Here is the documentation.

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But there are no additional surfaces. Its just a singlular zone. It has no attachments with any other surfaces

( 2018-09-05 08:36:11 -0500 )edit

Each interior wall in EnergyPlus is actually two surfaces, one for each face. Either way, you have a bigger problem on your hands as mentioned above.

( 2018-09-05 11:53:18 -0500 )edit