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Thread: Creating a Duct Accessory with both Supply AND Exhaust Connectors... how?

  1. #1
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    Unhappy Creating a Duct Accessory with both Supply AND Exhaust Connectors... how?

    Hi all,

    I work for a ventilation company and produce their Revit families. However, a newer piece of kit has proven more tricky than in expected.

    The item is basically a metal box, partitioned into 4 quarters that sits in the ceiling void and has all 4 ducts connected to and from it from a residential style HRU unit. Therefore it has both supply AND extract air systems running through it though it has not mechanical function, it's just ducting really.

    The problem is it has 4 supply connectors and 4 extract connectors. (2 in and 2 out for each system).
    This is proving very tricky when assigning their duct connector properties and Revit is not liking what I have tried so far.

    - Having 4x Supply and 4x Exhaust connectors means Revit doesn't know which ones are connected and I know that the 'Link Connectors' button should not be used on anything other than 'Global' connectors.

    - Assigning either 'Fitting' or 'Global' to the connectors (linking and not linking them) means that as soon as the first piece of duct is connected to the unit, the entire unit becomes a supply unit, not allowing an exhaust system as well.

    - Assigning the classification 'Other Air' to the connectors does allow both supply and exhaust systems to be connected but for some reason the airflows from the air valves do not get fed back to the HRU meaning manual input is needed and therefore not ideal

    How would you approach this guys?...

    ...I'm stuck


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  2. #2
    Member evan.dodds's Avatar
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    I think you should have a different flow parameter for each connector. Then you can give the supply in and exhaust out parameters a formula to sum the flows from their respective outlet/inlet connectors

    Sent from my Nexus 5 using Tapatalk

  3. #3
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    Unfortunately I had already done that. However I seem to have fixed the issue. I had to set the two room side connectors (not the ones going down to the HRU) to Calculated and all the other 6 to Preset in the classification dropdown. Unfortunately I do have to have two separate models because of "this, that and the other" but at least it is now working
    Thanks for your suggestion.

  4. #4
    Mr. Revit OpEd
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    I'm curious, did you try to use Link Connectors? I thought that not using that feature was related to finding it being used where there is no ambiguity between inlet and outlet path. For example some of the stock VAV units used it between Supply In and Out when there were no other connectors. That resulted in an error that would not let the system calculate flow.

    In this case, it seems that your situation is exactly the purpose of Link Connectors; to define the path between inlet and outlet when there is more than one possible path to follow.

  5. #5
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    I have just tried linking the supply and extract connectors (as they would be in real life). Unfortunately it then stops feeding back the 'live' airflow values of the valves to the HRU.

    The HRU maintains the airflow values it had before the change but no longer receives any new changes. The help files for revit do actually state "Linked connectors only have an effect when the System Type is set to Global"

    It probably should say "only have the correct effect when set to global". Because the effect it had just now when linking dedicated supply and extract connectors was to make them not work properly

    Thanks for the suggestion though.

  6. #6
    Member evan.dodds's Avatar
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    Quote Originally Posted by mrgrotey View Post
    Unfortunately I had already done that. However I seem to have fixed the issue. I had to set the two room side connectors (not the ones going down to the HRU) to Calculated and all the other 6 to Preset in the classification dropdown. Unfortunately I do have to have two separate models because of "this, that and the other" but at least it is now working
    Thanks for your suggestion.
    I forgot about flow configuration.... Pretty sure this would be the correct flow configuration setup for your system, in case you don't have it set up:

    The HRU connectors that are attached to the room side would be calculated with the box connectors set to preset. The two room diffusers would be preset while their box connectors would be calculated (as you say you have it).

    The HRU connectors for the louvre (?) side would be set to preset with the HRU side box connectors set to calculated and the louvre side set to preset. The louvres would have their connectors set to calculated.

    Then you should only need four flow parameters in the box each assigned to the two connectors in each branch.
    Last edited by evan.dodds; August 3rd, 2017 at 05:45 PM.

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