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  1. #1
    Join Date
    Feb 2006
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    Float'N Vally, MS
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    AirFlow problem - lab

    Ok - This is out of the box and whomever designed it needs to be shot....
    That said.

    We have a Carrier 50ZHB042 on about 60' of buried 12" fiberglass round pipe (RA & Discharge)(long story).
    Supply static <> .89 with 780 cfm with no filters.
    There is no way this unit is going to push enough air (that I know of).

    Thinking outside the box for an answer?
    No equipment can be put on the inside of the building.
    Life is too short, Behappy!
    TFMM

  2. #2
    Join Date
    Jul 2012
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    WA
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    Is all the ductwork buried? Is there any way to put an in line fan on the outlet?

  3. #3
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    Feb 2006
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    Float'N Vally, MS
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    Quote Originally Posted by Red Man View Post
    Is all the ductwork buried? Is there any way to put an in line fan on the outlet?
    I don't believe we can have ANY equipment in the building.
    If we could, I assume it would have to be 2 fans (RA/DAS)?
    Life is too short, Behappy!
    TFMM

  4. #4
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    Jul 2012
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    WA
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    This is a package heat pump right? The ducts come out the back? I assume the unit is outside. Is there no room around the unit to add the booster fan?

  5. #5
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    Quote Originally Posted by Red Man View Post
    This is a package heat pump right? The ducts come out the back? I assume the unit is outside. Is there no room around the unit to add the booster fan?
    Yes, when you say add a booster fan are you talking another blower fan after the unit discharge?
    Would you need something on the RA also?
    Like push/pull?
    Trying to wrap my head around this.
    Life is too short, Behappy!
    TFMM

  6. #6
    Join Date
    Feb 2003
    Location
    Madison, WI
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    I would consider changing out the indoor blower assembly for the 5 ton blower. The cabinet sizes are the same for 3.5 ton through 5 ton so the blower should fit. The 5 ton has a larger (wider) wheel and a 1 hp motor instead of the 1/2 horse of the 3.5. This should effectively give you a high static pressure system to overcome duct loss. I am unsure if this would overcome the return system restrictions. I have done this on Trane rooftops with good success (but Trane has all the part numbers to convert existing units to high static units).

  7. #7
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    Jul 2012
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    WA
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    I think you'd be ok with discharge only. You should be able to find a 12" round one. If the blower in the unit is an ecm you need to take it out. I'd probably look for a fan that could move the required air itself and remove the blower from the unit.

  8. #8
    Join Date
    Feb 2016
    Location
    Louisburg Kansas
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    Displaced Texan gave good advice. It does appear you have some sort of restriction in the duct system. A 12 inch duct 60 feet long conveying 780 CFM of air should only generate a little over 0.07 inch of static (main duct only). The type of fans used in these units will normally not produce more than 0.5 inches of total static without significant reduction of air flow. If you replace the fan and motor be sure it is rated for at least 1.0 inch of static. Sizing fans for series operation can be tricky.

  9. #9
    Join Date
    Feb 2004
    Location
    New Mexico
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    Determine how much air you need to move and that will be the beginning of a solution.

    What goes out also has to come in. The supply and return need to be at least similar in capacity.
    A 12" duct with a normal fan is about where you are. Is the fan a PSC?
    I should have played the g'tar on the MTV. MK

    You can be anything you want......As long as you don't suck at it.

    SMW Lu49

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