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Thread: Correct Classification for Duct Connectors for an HRU Air Handling Unit

  1. #1
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    Question Correct Classification for Duct Connectors for an HRU Air Handling Unit

    Hi there guys,

    I have had a customer of mine come back with some 'constructive criticism' that my heat recovery unit duct connectors are not set up correctly so I was wondering if anyone could shed some light.

    The supply airflow though the units has both the in and out connectors set to 'Supply Air' in the System Classification drop down.
    The extract airflow through the unit has both the in and out duct connectors set to 'Exhaust Air'.

    What the customer is saying is that (and I quote) "you can't connect any grilles to the system because it should be on a 'Return Air' system".

    Is this correct? Should all my extract connectors be set to 'Return Air' rather than 'Exhaust Air'. This is the first time anyone has mentioned this.

    Can the difference between Return and Exhaust be explained please? I have tried searching for this but the help files don't seem to explain this, they just say these are the options rather than any description of each setting.

    Thanks very much.

    Michael
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    Last edited by mrgrotey; July 24th, 2015 at 09:01 AM.

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    Return is air that's being recirculated back to the unit. Exhaust (or extract) is being expelled from the building. In your case, I agree with you, the HRV should have Exhaust and Supply connectors. They should be connecting Exhaust Air Terminals to that system. But you could just easily make it all Return as well. It's all semantics, really. The only important thing is that you don't mix the two.

    I'm curious, does this family calculate leaving air temperatures? If not, you could get it to do so rather easily. Also, what's the 15mm Hot Water connection for?

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    Revit has separate Return and Exhaust "duct systems" among the others to accommodate typical air streams found in a building. In this example there are two, the used but non-contaminated "return" air that is reconditioned and sent back to the building, and then there is the used and contaminated "exhaust" air discharged outside the building.

    Heat recovery units are most often used for exhaust air streams so I can understand your reasoning, but there may be a case where the return air stream is the source. This may be your clients case. If so he is using return grilles with return connectors that gives him a warning when connecting to your "exhaust" connector on your equipment.

    Revit desires all connectors communicating via a common network of ductwork to be of the same "duct system" from the source (grilles) to the equipment (HRU in you case). You could set your Extract Inlet connector to global in lieu of exhaust. That will allow any duct system to connect to it. Your client could also open the family and change it to return air.

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    Thanks very much to you both for the detailed responses that's great, I'm glad I was doing the right thing. I must say that most of the units we see are used for discharging the extracted air to the atmosphere so I guess the customer in this case expected some element of psychic power on my part knowing he wanted it for recirculating it

    thanks again that was exactly what I needed.

    michael

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    Quote Originally Posted by Necro99 View Post
    Also, what's the 15mm Hot Water connection for?
    Ah yes, thanks for bringing my attention that that, its the strangely incorrect setting given to the condensate drip connection. I have corrected this and set it to global. Not sure what happened there.

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    Hi Michael,Are you able to run calculation through your HRU family ? Did you use a Links between connectors??
    Quote Originally Posted by mrgrotey View Post
    Hi there guys,I have had a customer of mine come back with some 'constructive criticism' that my heat recovery unit duct connectors are not set up correctly so I was wondering if anyone could shed some light.The supply airflow though the units has both the in and out connectors set to 'Supply Air' in the System Classification drop down.The extract airflow through the unit has both the in and out duct connectors set to 'Exhaust Air'.What the customer is saying is that (and I quote) "you can't connect any grilles to the system because it should be on a 'Return Air' system".Is this correct? Should all my extract connectors be set to 'Return Air' rather than 'Exhaust Air'. This is the first time anyone has mentioned this.Can the difference between Return and Exhaust be explained please? I have tried searching for this but the help files don't seem to explain this, they just say these are the options rather than any description of each setting.Thanks very much.Michael

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