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Thread: Duct Connector to read calculated total CFM of the connected diffusers?

  1. #1
    Forum Addict tzframpton's Avatar
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    Question Duct Connector to read calculated total CFM of the connected diffusers?

    Hello all,

    I'm using some default OOTB Autodesk content here. This project is our "whipping boy" project that a few of us use to test things in our down time. I added four 8" dia. diffusers and aggressively made them 100 to 400 CFM just to see the main duct branch change size based off the velocity FPM. Works great. All of these diffusers are connected to a VAV which is a secondary system. The primary system is the Air Handling Unit.

    Right now the duct connectors on the secondary VAV system is a CFM Parameter and it's Instance Based, which is a value that is user-defined. When I select each individual round duct connected to each diffuser I can see the flow is being calculated which is 400 CFM. This totals to 1,600 CFM on the main branch but when I select the main branch it reads "Multiple Values". Even though it displays multiple values, all the CFM's are calculated correctly in the Systems Browser. But the CFM on the Mechanical Equipment is manually controlled.

    So two part question here.... (1) why does it show "multiple values" instead of showing all the connected CFM and (2) is there a way to get the total calculated CFM to be parametrically controlled on the duct connector? The reason for this is because in the scheduling process, it would be super duper awesome if I could have our "Max CFM" column totally controlled parametrically, based on the total CFM's with all the connected diffusers. This way there's no discrepancy between Plan View CFM's and Max CFM in our equipment schedules.

    Sorry it's so lengthy and I've attached screens for reference. Thanks in advance! -Tannar
    Attached Thumbnails Attached Thumbnails Duct Connector to read calculated total CFM of the connected diffusers?-01.png   Duct Connector to read calculated total CFM of the connected diffusers?-02.png   Duct Connector to read calculated total CFM of the connected diffusers?-03.png  

  2. #2
    Mr. Revit OpEd
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    The air terminals air flow sum arrives at the VAV but the air flow for the VAV is manual because it is up to you to decide what unit you are going to use in response to the total air flow load on it. Same thing with electrical panels, you see what the connected load is and decide if the panel is still large enough. I think the multiple values in your example is the result of entering different air flow for each air terminal.
    Last edited by Steve_Stafford; July 8th, 2013 at 11:03 PM.

  3. #3
    Forum Addict tzframpton's Avatar
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    Quote Originally Posted by Steve_Stafford View Post
    The air terminals air flow sum arrives at the VAV but the air flow for the VAV is manual because it is up to you to decide what unit you are going to use in response to the total air flow load icon it. Same thing with electrical panels, you see what the connected load is and decide if the panel is still large enough. I think the multiple values in your example is the result of entering different air flow for each air terminal.
    That makes sense. I can see how this is a better situation so you don't get lazy and have a Max CFM that will overload the equipment. What's good is all the CFM's do add up in the Systems Browser so it's easy to check your Max CFM that has been inputted on the equipment. Attached is an overall screen of my test project and everything is connected, and all duct was sized accordingly. I'm very impressed with how well it all went.

    Thanks again Steve.
    Attached Thumbnails Attached Thumbnails Duct Connector to read calculated total CFM of the connected diffusers?-overall.png  

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