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Community and Q&A

Is this a good HVAC design?

Rick Fetter | Posted in Mechanicals on

I would like comments on the Manual J & D that was done for me and the duct work design that is attached. My house is located in zone 5A at 3160 elevation.

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  1. Ethan Foley | | #1

    Taking a very brief look at it, the simple answer is no. The design static pressure the designer has used is 0.51 in.wc. Your unit can supply a maximum 0.36 in.wc. This is a major error.

    Other criticisms might include:

    Don't use flex duct when hard sheet metal ducting would be a much better substitution.

    Don't take branches off the end cap of a trunk. This makes the trunk very difficult to balance.

    Drawing too much return air from the master suite, the additional air needed can't flow through a typical door undercut.

    The CFM specified is not an actual flow rate produced by this unit.

    That's my takeaway from a brief look.

  2. Jon R | | #2

    Ask them what sensible heat ratio (this effects humidity) you are going to get at 1/2 load (a much more common operating point than 100% load) and let us know the answer.

    The ducts are under-sized. Consider moderate over-sizing of all of the ducts. This will reduce fan power, improve balance as flow changes and provide additional flexibility in adjusting balance.

  3. Rick Fetter | | #3

    Thanks for your reply but I cant get the designer to respond to me now. Dana Dorset gave me the information on the Fujitsu unit but I am not an HVAC guy. I am a little surpprised at the lack of response to my question, I will put this in the mechanical section. I hope someone will respond with some more detailed information and contact info that we can correspond. ( not sure that allowed on GBA)?

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