Pretreated Outside Air system Question

[mmcglone]

I have a 100% outside air unit that I am pretreating my fresh air with.  The problem comes when I duct the supply of the OA unit to the return of my indoor units.  Should I model the duct as return or as supply?  Revit seems to think that half the supply duct from the OA unit is return, and won't let me change it.  Any Suggestions?

[Jrobker]

Which RVT version are you using?

Can you post a picture?

When you said, "won't let me change it" It is because the connector must be defined as return.

Where did you get the equipment? Manufacturer or you modeled it?

Creating systems like the one you are describing can be difficult. Just creating a basic system with AH to VAV can be testing. Some things you just cannot do and you may have run into one of those.

Are you using RVT to size you duct and create schedules?

[mmcglone]

I am using MEP 2012.  The equipment is from the manufacturer.  The  problem comes from supply duct connecting to return duct. It won't let me change the duct because it is connected to a return air system.  I tried using the system editor to deselect the OA supply duct to no avail.  I attached a picture with just one supply and return system.

[l.hammarback]

I think i know how to fix that.  First off there are...4 i think base types of duct systems, supply, return, exhaust, other.  And if you make a new system called OA, i would bet you would use supply.  So the connector needs to be supply as well.  You can change the connector to supply if you edit that model.

Another thing you can try is not to draw the ductwork by clicking on the connector and then rightclick draw.  Instead, draw the ductwork first away from that equipment and then before connecting, specify the system that it is in.  Then connect it to the equipment.  You'll have to go back and be sure that the equipment your connecting to is in fact the "equipment" for the OA system.

[embolisim]

It sounds like you are trying to change systen type mid duct run. I.E. connect a supply system duct into A return system duct. You cant do this.

If a  duct run can 'see' more that one different connector type you will have problems.

The way around this is to use a family to change the system type.

Presumably you have dampers where the two ducts connect, so you can use the damper on the supply duct to convert it to a return system, by havving a supply connector on the inlet & a return connector on the outlet. 

Make sure you make a copy of your damper family before you change it, or all your other dampers will change in the same manner when you reload it.....

[asommer · Accepted solution]

That's what I use, we have this situation on almost every project. Use the Balancing Damper, create flow parameters for the inlet and outlet connectors. Do not Link them, just have the Return CFM = Supply CFM. Also, if you are using the "Systems", Change the Family Category to "Air Terminals". This will let it show up in the systems dialog.

[Jrobker]

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@asommer wrote:
 if you are using the "Systems", Change the Family Category to "Air Terminals". This will let it show up in the systems dialog.

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This is a good tip, but I see 1 issue.

If the Architect makes an RCP plan with our diffuser locations how can they turn off the dampers?

Do you put them on a sub-category of air terminals?