changing the CFM, value turns red in Modify Duct dialog box

[robert.mccarty]

First off my field is Electrical but I am trying to learn every aspect of ABS that I can. I changed the Capacity (CFM) of a main branch of Supply Duct in the Modify Duct dialog box. When I did, the value I entered went from black to red. I did notice when I changed that value, the friction, along with the velocity changed as well. Obviously something is wrong with what I entered. All I did was change the CFM from 1200 to 1600. Can someone please help explain in the area of Mechanical. Thanks!

[robert.mccarty]

Can anyone from AutoDESK help??

[Wanderer]

Can anyone from AutoDESK help??this is a peer to peer support group. autodesk employees may chime in every now and again, but, it's not a realistic expectation.

Now, to speculate on the answer to your question, I haven't installed ABS yet, but, going from black to red typically means going from good to bad, yeah? Maybe you've just upped your capacity to more than what that equipment is told it can supply.

Maybe if you select properties of that readout you'll get access to a relevant helpfile?

Good luck on an answer.

[jlwetzel]

the reason it is red is because you have an open end of duct along the way. if you place endcaps it should go away. Another reason may be that you have a terminal device (vav box) without a flow assigned connected to the system.

Also another note, changing the capacity of the duct manually does nothing. What happens is the main duct adds all the cfm values that are connected to it and ahead of it. This means you have to assign the correct cfms to vav boxes and air devices to acheive the correct number.

[robert.mccarty]

Thanks for the reply. I thought it might be endcaps as well but with the default value of 1200 cfm the numbers are black. When I change the value to 1400 or 1600 cfm, the numbers turn red. I believe this to be more of an HVAC design error than an ABS error.

[rlanear]

You are absolutely correct. The duct system design parameters and associated equipment including CFM distribution on the system impact what is allowed to happen with the MVDuct modify
cfm

[Wanderer]

looks like the OP did get some additional input on the autodesk forums (http://discussion.autodesk.com/thread.jspa?messageID=5330775) that might interest some folks.