Revit MEP

Reply
Member
brcannas
Posts: 5
Registered: ‎08-27-2012
Message 1 of 9 (765 Views)
Accepted Solution

Problem with ducts splitting and sizing

765 Views, 8 Replies
08-27-2012 02:29 AM

Hello all, I've just started learning Revit MEP (mainly for duct systems) and I found the following problem:

 

On my project I did a HVAC system with rectangular ducts and I noticed that the duct sizing tool does not split the ducts after a branch (it should do that because after the branch it has less air flow and this will change the air velocity if the size stays the same - correct me if I'm wrong -) so I started to look for a way to split the ducts manually and then use the sizing tool again.

The only way I found to split the ducts was placing rectangular conections after each branch, and after using the sizing tool I got what I wanted.

The problem is that now there's and error message saying that the system is not "well connected" but it won't show me where it is disconnected like it usually does, and because of that error I can't use the system inspector on the system (other than that I didn't find any problems).

Any ideas on what the problem is or how to split the ducts and size them properly without getting this error?

 

I'm attaching a picture of the error message but it's in portuguese, I can upload the project file if anyone's interested.

 

Thanks

 

(I'm using Revit MEP 2012 Educational)

The "well connected" issue is one that has been around for ever and Autodesk are not very forth coming in explaining how or why this happens and what can be done to solve/prevent this.

 

Try deleting the system and rebuilding it. That sometimes solves the problem. One way to find out where the problem lies is to gradually build the system starting with the furthest Air Terminal and Mechanical Equipment then adding one terminal at a time.

Sometimes I find that the shoes/taps can cause ducts to move out of perpendicular alignment which introduces minor angle errors. i.e instead of 90 degrees you get 89.99999947 degrees!!

Also check that all ducts are at the correct angles to each other.

Load the Ashrae table viewer either from Autodesk Labs or from the subscription centre. Then you can see what sizes are acceptable for the fitting. If the duct sizes conencted to the fitting are outside of the table's ranges then you get no value.

Another way to fix it would be to specify either a loss value or a loss coefficient, if you have these from an external source. That should then make the system well connected and also allow system inspection and therefore calculate stuff.

Valued Mentor
julianjameson8403
Posts: 458
Registered: ‎06-16-2010
Message 2 of 9 (736 Views)

Re: Problem with ducts splitting and sizing

08-28-2012 03:23 AM in reply to: brcannas

The "well connected" issue is one that has been around for ever and Autodesk are not very forth coming in explaining how or why this happens and what can be done to solve/prevent this.

 

Try deleting the system and rebuilding it. That sometimes solves the problem. One way to find out where the problem lies is to gradually build the system starting with the furthest Air Terminal and Mechanical Equipment then adding one terminal at a time.

Sometimes I find that the shoes/taps can cause ducts to move out of perpendicular alignment which introduces minor angle errors. i.e instead of 90 degrees you get 89.99999947 degrees!!

Also check that all ducts are at the correct angles to each other.

If my reply answers your query, please use the Accept as Solution.
Please give Kudos as appropriate to enhance the value of these forums.

Thank you!
Member
brcannas
Posts: 5
Registered: ‎08-27-2012
Message 3 of 9 (733 Views)

Re: Problem with ducts splitting and sizing

08-28-2012 03:32 AM in reply to: brcannas

Thank you for the reply! I followed your advice and started deleting sections to see where the problem was and I found out that the problem was the piece marked on the attached image, I deleted it and used branch connectors to replace it.

Valued Mentor
julianjameson8403
Posts: 458
Registered: ‎06-16-2010
Message 4 of 9 (729 Views)

Re: Problem with ducts splitting and sizing

08-28-2012 03:37 AM in reply to: brcannas

Hopefully you didn't delete the actual duct work sections only the system in the system browser and then gradually re-built the system  itself - should have explained that more clearly in my initial response.

Strange that that duct fitting cause problems - as it should be no different in priciple to a square Tee, except for the Ashrae table the fitting refers too. Unless you have specified a size of fitting that is not allowable within the Ashrae table.

If my reply answers your query, please use the Accept as Solution.
Please give Kudos as appropriate to enhance the value of these forums.

Thank you!
Member
brcannas
Posts: 5
Registered: ‎08-27-2012
Message 5 of 9 (726 Views)

Re: Problem with ducts splitting and sizing

08-28-2012 03:57 AM in reply to: julianjameson8403

Now that you mentioned I noticed that this fitting has a blank "ASHRAE Table" attribute, while every other fitting I used has something like SR4-1, I guess my ASHRAE table files doesn't include this fitting

Valued Mentor
julianjameson8403
Posts: 458
Registered: ‎06-16-2010
Message 6 of 9 (724 Views)

Re: Problem with ducts splitting and sizing

08-28-2012 04:23 AM in reply to: brcannas

Load the Ashrae table viewer either from Autodesk Labs or from the subscription centre. Then you can see what sizes are acceptable for the fitting. If the duct sizes conencted to the fitting are outside of the table's ranges then you get no value.

Another way to fix it would be to specify either a loss value or a loss coefficient, if you have these from an external source. That should then make the system well connected and also allow system inspection and therefore calculate stuff.

If my reply answers your query, please use the Accept as Solution.
Please give Kudos as appropriate to enhance the value of these forums.

Thank you!
Member
brcannas
Posts: 5
Registered: ‎08-27-2012
Message 7 of 9 (718 Views)

Re: Problem with ducts splitting and sizing

08-28-2012 05:51 AM in reply to: julianjameson8403

I can't find the problem, I changed the sizes and now the ASHRAE table field is filled, everithing is connected but the problem still persists.

Valued Mentor
julianjameson8403
Posts: 458
Registered: ‎06-16-2010
Message 8 of 9 (715 Views)

Re: Problem with ducts splitting and sizing

08-28-2012 06:07 AM in reply to: brcannas

ave you re-built the system in the system explorer as per previous post?

If my reply answers your query, please use the Accept as Solution.
Please give Kudos as appropriate to enhance the value of these forums.

Thank you!
Member
brcannas
Posts: 5
Registered: ‎08-27-2012
Message 9 of 9 (705 Views)

Re: Problem with ducts splitting and sizing

08-28-2012 06:53 AM in reply to: julianjameson8403

Oh, I thoght I had to remove the air suppliers and then add them again on by one, now I see what you mean.

I did that and it worked

 

Thank you very much!

Post to the Community

Have questions about Autodesk products? Ask the community.

New Post
Announcements
Do you have 60 seconds to spare? The Autodesk Community Team is revamping our site ranking system and we want your feedback! Please click here to launch the 5 question survey. As always your input is greatly appreciated.