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  1. #1
    Join Date
    Dec 2010
    Location
    New Orleans
    Posts
    1,012

    7.5 ton unit need help

    I have a restaurant cust. that has an above t-bar air handler [Old] no name plate left. TXV slant coil with a trane 7.5 ton condenser. The problem is air flow. When system installed the installer hooked a 16 inch return to to air handler which is way too small. The compressor was changed about one yr ago, before I inherited. My question is; would disconnecting return flex duct and using t-bar ceiling as return, increase the air flow? I believe it would, but before I dive in would like some feedback please.

  2. #2
    Join Date
    Aug 2007
    Location
    Northern VA 38 degrees N by 76 degrees W
    Posts
    5,060
    Quote Originally Posted by keeplearnin View Post
    I have a restaurant cust. that has an above t-bar air handler [Old] no name plate left. TXV slant coil with a trane 7.5 ton condenser. The problem is air flow. When system installed the installer hooked a 16 inch return to to air handler which is way too small. The compressor was changed about one yr ago, before I inherited. My question is; would disconnecting return flex duct and using t-bar ceiling as return, increase the air flow? I believe it would, but before I dive in would like some feedback please.
    Firs start with what type of material is above the ceiling.

  3. #3
    Join Date
    Jul 2011
    Location
    East coast USA
    Posts
    973
    Quote Originally Posted by second opinion View Post
    Firs start with what type of material is above the ceiling.
    If you pull air from a plenum, wiring in the ceiling needs to be fire rated. than you need a smoke detector on the return. Unless its not considered a fire rated plenum. check code

  4. #4
    Join Date
    Jul 2007
    Location
    Mount Airy, MD
    Posts
    7,281
    Being that it is a restaurant what does it have in place to run 365?

    Hot gas? Auto reset Freeze stats on the Evap? Condenser fan control? etc?

  5. #5
    Join Date
    Dec 2010
    Location
    New Orleans
    Posts
    1,012
    Freeze stats on coil, no smoke alarm in return. I think there might be a prob with a restriction at txv screen, I have replaced driers already and pressures way off. There does exist a smoke detector laying on t-bar??? who knows why, Remember New Orleans is the Big Easy and probably never inspected- you should see this place, terrible.

  6. #6
    Join Date
    Feb 2012
    Location
    Upstate SC
    Posts
    84
    An additional question that I would ask is how tight is the air space above the ceiling and is this a one story? You have the potential for creating a humidity problem given your location.

  7. #7
    Join Date
    Dec 2010
    Location
    New Orleans
    Posts
    1,012
    No two story and I would add return grills. Even though I know there exist a return air flow problem I am going to inspect txv screen and try to adjust the txv to get suction pressure up.

  8. #8
    Join Date
    Jan 2006
    Posts
    140
    I would drop a bunch of open top t-bar diffusers in to pull from the conditioned area, using the ceiling as a giant plenum. That would eliminate the humidity issues because it would still be pulling from the "comfort" area.
    The only decision in life is to decide what to do with the time given to you

  9. #9
    Join Date
    Dec 2003
    Location
    Citrus County, Florida
    Posts
    1,555
    If the area above the ceiling is not sealed, I believe you will be pulling all sorts of garbage and humidity into the return. Plenum returns are not advised. Why not add the proper ductwork? You short on return. Cure the airflow problem and then adjust the TXV and charge. What is the static pressure? I'll bet the return is out of sight.
    Doug

  10. #10
    Join Date
    Dec 2010
    Location
    New Orleans
    Posts
    1,012
    Quote Originally Posted by Gunslinger View Post
    If the area above the ceiling is not sealed, I believe you will be pulling all sorts of garbage and humidity into the return. Plenum returns are not advised. Why not add the proper ductwork? You short on return. Cure the airflow problem and then adjust the TXV and charge. What is the static pressure? I'll bet the return is out of sight.
    No room and I mean none.

  11. #11
    Join Date
    Jan 2007
    Location
    Stongsville Oh
    Posts
    899
    If you make a plenum return along with what everyone else mentioned you will increase the conditioned space area. Can the equipment handle the load?
    ckartson
    I didn't write the book I just read it!

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