Return Air Duct with Outside Air mixing

[Anonymous]

I am trying to create a duct system (existing system at a project I am evaluating).  The existing system is in a classroom and has a fan coil unit that takes a suction from 2 points in the space and incorporates outside air from a common header in the hallway. 

The problem is the outside air duct ties into the return ductwork right before the fan coil and Revit changes the tie-in piece to orange for return air instead of purple for outside air. 

How can I model this mixing chamber properly?  I have thought about using an AHU mixing box and changing one of the inlets to Global from Return air to accommodate the outside air. 

I am open to any suggestions.

Thanks!!!

[robert.klempau]

Hello,

I think I have a solution for you. I created a system for you so you can see what happens. I the Classroom I placed two Supply Air Terminals and Two Return Air Terminals and in the Hallway an object that produces the Outside Air. That could also be an Outside Air duct system.

You see three systems each with their own color.

There where the three systems come together I placed a mechanical Equipment that looks like a Tee.

I opened a Tee Fitting and changed the Category to Mechanical Fitting. I did that so I could connect three different systems to one object.

I removed the link between the connectors and changes the System Classification for each connector.

Connector 1:

System Classification = Return Air

Flow Configuration = Calculated

Flow Direction = in

Flow parameter = flow in con 1

Connector 2:

System Classification = Supply Air

Flow Configuration = Preset

Flow Direction = in

Flow parameter = flow in con 2

Connector 3:

System Classification = Supply Air

Flow Configuration = Calculated

Flow Direction = out

Flow parameter = flow out con 3

For parameter flow in con 2 I used formula:  flow out con 3 - flow in con 1

See my Video

Hope this is what you want.

I also uploaded the Project so you can have a close look at the system.

[sachinmenon1990]

hi,

i checked your project file as ,we too had such a requirement during our project work.

Although your are able to sum up all the flow from different systems ,the system Inspector is not able to inspect system as a whole.Instead the system inspector is considering it as 3 different systems.Refer attached image.

what we wanted was a way to not just to add the flow but show a single system where in we could connect fresh/outside air with return plenum or duct & a single or combined system inspector for it.

Also you have used a tee fitting, which works sort of does the job for this particular layout, but in our project the fresh or outside air was connected using shoe branch & even with different settings like you have tried , we could not get it to work. revit was not able to combine total flow & system inspector would also not appear.

so how do you propose we can solve problems in such cases as we are trying it from more of a site or practical point of view,because in reality they just connect the return & outside air and it works.So how can we do something similar in revit.

Thank you