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Creating Openings In Return Ducts Above Ceilings

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Message 1 of 19
tim102289
2291 Views, 18 Replies

Creating Openings In Return Ducts Above Ceilings

For a project we're working on at the office, they want a return duct that just connects the space above the ceiling in each room to the corridor.  I made the duct easily enough, but I was wondering if there is a way to put openings in the duct.  I need one on the end of the duct into the corridor, and one on the bottom of the duct in the room.  Essentially the air flows up into the duct, and then out into the corridr.  I've included a section view showing what I want to accomplish.

 

Section

Tim Smith
IT Manager, Mechanical Engineer  |  Motz Engineering

“There is nothing more expensive than hiring cheap engineers.”
Experienced in Revit MEP/AutoCAD/Sketchup | Autodesk BPA Certificate
18 REPLIES 18
Message 2 of 19
CoreyDaun
in reply to: tim102289

If you are working with a linked Architectural Model, then "No". Lighting designers would love to be able to cut the Ceilings in the Link Model, which hits the same dead-end answer.

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Message 3 of 19
tim102289
in reply to: CoreyDaun

I think you are misunderstanding my question.  I am working with a linked architectural model, but that isn't really relevant.  I just want to know if there is a way to make openings in the duct itself (a duct that I have drawn in the MEP model).  As you can see in the section drawing, the duct needs an opening on the end where it is in the corridor, and on the bottom where it is in the room, for the air to go into.  I was wondering if there was an easy way to do this, or if I need to make some kind of grille or fitting component that is simply a hole.

 

01.png

 

EDIT: I added another picture which may better illustrate what I mean.  The blue line shows the return air, which needs to go from the room out into the corridor.  The red would be the insulation on the duct.  The brown is the wall.  I just need to make an opening on the bottom of the duct in the room where the air goes in, and have the other end of the duct open, where the air goes out into the corridor.

Tim Smith
IT Manager, Mechanical Engineer  |  Motz Engineering

“There is nothing more expensive than hiring cheap engineers.”
Experienced in Revit MEP/AutoCAD/Sketchup | Autodesk BPA Certificate
Message 4 of 19
CoreyDaun
in reply to: tim102289

Yes. Yes I did. My apologies...

 

Duct Elements aren't actually hollow, though; they are just like solid Extrusions. (View the end of a Duct in a Section View [Detail Level: Medium or Fine] and turn off the Rise and Drop Subcategories to see what I mean). So even if you could "cut a hole in it", you'd also have to find a way to hollow out the rest of it. If you wish to depict an opening like that, then you'll need to model a simple Duct Accessory or Duct Fitting to accomplish that.

 

Edit: Rather than a decal, a Detail Item family hosted to the Duct face.

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Message 5 of 19
tim102289
in reply to: CoreyDaun

I guess really all I need to model is the opening on the bottom of the duct, so that the drop will show on the floor plans.  Then end of the duct would only need a fitting so that Revit believes the duct is complete and won't show an open connector.  I could probably do the end with a slightly modified end cap.  The other fitting might be tricky.

Tim Smith
IT Manager, Mechanical Engineer  |  Motz Engineering

“There is nothing more expensive than hiring cheap engineers.”
Experienced in Revit MEP/AutoCAD/Sketchup | Autodesk BPA Certificate
Message 6 of 19
CoreyDaun
in reply to: tim102289

Why not create a fitting that combines the endcap with the representation of the opening into a single Family?

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Message 7 of 19
tim102289
in reply to: CoreyDaun

You mean for the opening on the bottom of the duct or the end of the duct?  As far as the end of the duct in the corridor is concerned, I don't really need to show the opening.  It wouldn't be visible in plan view.  So I could just put an end cap on that end.  I might modify it so that it doesn't appear in the drawings as an endcap, so that there is no confusion about the duct being closed off.  As for the other end, I could probably use an endcap for that as well, I would just need to include some kind of symbol or something in the family to show the dotted line box with the slash in it, representing a drop for a return duct.

Tim Smith
IT Manager, Mechanical Engineer  |  Motz Engineering

“There is nothing more expensive than hiring cheap engineers.”
Experienced in Revit MEP/AutoCAD/Sketchup | Autodesk BPA Certificate
Message 8 of 19
tim102289
in reply to: tim102289

The end of the duct with the opening on the bottom, is actually like a rectangular elbow I guess.

Tim Smith
IT Manager, Mechanical Engineer  |  Motz Engineering

“There is nothing more expensive than hiring cheap engineers.”
Experienced in Revit MEP/AutoCAD/Sketchup | Autodesk BPA Certificate
Message 9 of 19
CoreyDaun
in reply to: tim102289

I would make a copy of the OOTB Rectancular Endcap and start from there. First off make the Endcap geometry (the Extrusion) invisible (remove the symbolic lines, too). Then, you can model the opening in this Family (refer to the images below). You can host the Extrusion to a Reference Plane that is at the bottom of the Duct (formula is Duct Height / 2). Model the size of the opening in the Ref. Level view however you wish, and even give it a variable offset from the end of the Duct. Now, this family not only represents your "opening", but it tells Revit that the duct is not "open-ended".

 

EndCapOpening.JPG

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Message 10 of 19
tim102289
in reply to: CoreyDaun

I ended up just copying the endcap family, and unchecking "Visible".  Then I placed a "Rectangular Sharp Throat Radius Heel Elbow - DTL" with a "Straight In" and "Straight Out" value of 0 inches.  I then added 1 inch of vertical duct to the bottom (since I have 1" insulation on the duct, this made the opening flush with the bottom of the duct).  This gave me a drop on the floor plan.  Then I just put one of my 'invisible' end caps on each end, and voila.  The only issue there might be is that because the endcap is invisible, if you ever need to remove one or delete one, you won't be able to click on it.  But other than that, it all worked out okay I believe.

 

01.png

Tim Smith
IT Manager, Mechanical Engineer  |  Motz Engineering

“There is nothing more expensive than hiring cheap engineers.”
Experienced in Revit MEP/AutoCAD/Sketchup | Autodesk BPA Certificate
Message 11 of 19
tim102289
in reply to: tim102289

I may have run into another issue with this.  Because both ends of the duct are capped, and the duct isn't connected to anything, the system type is undefined, rather than being return air...

Tim Smith
IT Manager, Mechanical Engineer  |  Motz Engineering

“There is nothing more expensive than hiring cheap engineers.”
Experienced in Revit MEP/AutoCAD/Sketchup | Autodesk BPA Certificate
Message 12 of 19
CoreyDaun
in reply to: tim102289

Can you just leave the Duct "uncapped" on the corridor side?

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Message 13 of 19
tim102289
in reply to: CoreyDaun

Well I mean I can leave it uncapped on both ends, it's just that Revit will show it as being an open connector.

Tim Smith
IT Manager, Mechanical Engineer  |  Motz Engineering

“There is nothing more expensive than hiring cheap engineers.”
Experienced in Revit MEP/AutoCAD/Sketchup | Autodesk BPA Certificate
Message 14 of 19
CoreyDaun
in reply to: tim102289

Try changing the Duct Connector's 'System Classification' to "Return Air". When I tested this, I drew a Return Duct and attach this "cap" at both ends and it remained on the Return Air System, instead of becoming "undefined".

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Message 15 of 19
tim102289
in reply to: CoreyDaun

I don't follow what you're saying.  As soon as I place the second cap, the system type changes to Undefined.

Tim Smith
IT Manager, Mechanical Engineer  |  Motz Engineering

“There is nothing more expensive than hiring cheap engineers.”
Experienced in Revit MEP/AutoCAD/Sketchup | Autodesk BPA Certificate
Message 16 of 19
CoreyDaun
in reply to: tim102289

OK. I had placed an instance of that same modified Family on both ends of the Duct and it to remain on the Return System. This indicates that you'll need to also create a special " Endcap (Return)" family in which the Connector is also set to Return. It seems that if the caps on BOTH ends are set to the same classification, it does not revert to "Undefined".

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Message 17 of 19
tim102289
in reply to: CoreyDaun

How do you set the Endcap to be Return?

Tim Smith
IT Manager, Mechanical Engineer  |  Motz Engineering

“There is nothing more expensive than hiring cheap engineers.”
Experienced in Revit MEP/AutoCAD/Sketchup | Autodesk BPA Certificate
Message 18 of 19
CoreyDaun
in reply to: tim102289

Open the Family for Editing and change the System Classification of the Duct Connector. That's why I recommend creating a copy of the normal Endcap Family.

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Message 19 of 19
tim102289
in reply to: CoreyDaun

Ah that worked, awesome.  I was having trouble finding that System Classification parameter in the family, then I figured out what you were saying.  I thought you were referring to the endcap itself as the "Duct Connector," and when I opened the family I didn't see System Classification listed anywhere in the properties.  Then I realized that you were talking about the Duct Connector piece in the family, and once I selected that I saw it, changed it from Fitting to Return Air.  That did the trick, it stays in the Return Air system, and even when copying the whole system, it stays Return Air.  Thanks for your help.

Tim Smith
IT Manager, Mechanical Engineer  |  Motz Engineering

“There is nothing more expensive than hiring cheap engineers.”
Experienced in Revit MEP/AutoCAD/Sketchup | Autodesk BPA Certificate

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