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  1. #1
    Join Date
    Jul 2005
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    south
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    641
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    Adding dehumidification to 40 ton package unit

    So here's the situation

    church sanctuary feed by a Trane 40 ton package unit.
    Unit is 2 stage dx cooling 2 stage electric heat.
    1st stage 15 tons 2nd stage 25 tons.
    Thermostatic expansion valves and intertwined evaporator.

    unit sized for full capacity during occupied times but during unoccupied times
    unit maintains set point but has short run cycles, creating high humidity(>68%)
    positive building pressure has been verified.


    What would be the better option to control humidity ?

    1. Rawal device on 1st stage circuit ?
    2. Install vfd on evaporator motor and run preset speeds for 1st and 2nd stage cooling ?
    3. install controls to bang on electric heat strips for reheat control ?
    4. Hack in a hot gas reheat coil ?

    side note---- due to building and duct design there is no possible option to add a stand alone dehumidifier

    I'm game for any suggestions

  2. #2
    Join Date
    Dec 2004
    Location
    Chicago area
    Posts
    4,495
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    Rawal device for sure.


    Sent from my iPhone using Tapatalk

  3. #3
    Join Date
    Dec 2014
    Location
    midwest
    Posts
    1,574
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    Couple more.
    Add HGBP to circuit?
    EPR?

    Subscribing.

    Sent from my SM-G930V using Tapatalk

  4. #4
    Join Date
    Dec 2004
    Location
    Chicago area
    Posts
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    HGBP would be a lot of work, and increase utility bills more then rawal.

    Epr might work, but thats not really its purpose.

    Rawal was designed for this exact application.


    Sent from my iPhone using Tapatalk

  5. #5
    Join Date
    Dec 2004
    Location
    Chicago area
    Posts
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    Electric reheat with cooling is a bad idea. Good chance for sparkage if heating air thats nearly 100 percent humidity comming off the coil, and they may even have condensate on them.


    Sent from my iPhone using Tapatalk

  6. #6
    Join Date
    Nov 2014
    Location
    Northern Idaho
    Posts
    406
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    Adding dehumidification to 40 ton package unit

    What is a Rawal?

    Edit: nevermind, found it online. Looks pretty cool, heatingman have you installed them yourself before?


    Sent from my iPhone using Tapatalk

  7. #7
    Join Date
    Jan 2007
    Location
    Stongsville Oh
    Posts
    1,395
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    I don't gett what good hot gas bypass or the Rawal hgbp will do for dehum. Either will just raise evap coil temperature? I have added rawal to many systems but not for the purpose of dehum.
    ckartson
    I didn't write the book I just read it!

  8. #8
    Join Date
    Dec 2014
    Location
    midwest
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    Yes most of the options will increase evap temp, but longer run time is what he's after . So there'll be a higher ADP but much longer run time, allowing more moisture removal.

    The VFD option is pretty straight forward. Set at lowest Manufacturer cfm. May need to add an accumulator too. I've done that method. It worked well.

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  9. #9
    Join Date
    Dec 2012
    Location
    columbus, OH
    Posts
    4,603
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    Number 3 for sure. Super easy

    Sent from my SM-S320VL using Tapatalk

  10. #10
    Join Date
    Dec 2004
    Location
    Chicago area
    Posts
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    Quote Originally Posted by GoCougs View Post
    What is a Rawal?

    Edit: nevermind, found it online. Looks pretty cool, heatingman have you installed them yourself before?


    Sent from my iPhone using Tapatalk
    Yes. I have installed them. They work well if there sized properly - involve rawal in the selection, and it will work like a champ.

    Just add valving to close it off to check charge easier.

    Essentially what it does is add a secondary path for hot gas refrigerant to flow directly back to the compressor. There website explains in much better, but essentially the refrigerant flow to the evaporator gets reduced, so it slows down causing an increase in evaporating temperature- which is adjustable. This reduces evaporator capacity which allows for longer run times and as a byproduct better humidity control.


    Sent from my iPhone using Tapatalk

  11. #11
    Join Date
    Jun 2003
    Location
    Madison, WI/Cape Coral, FL
    Posts
    8,241
    Post Likes
    Quote Originally Posted by licensed to chill View Post
    So here's the situation

    church sanctuary feed by a Trane 40 ton package unit.
    Unit is 2 stage dx cooling 2 stage electric heat.
    1st stage 15 tons 2nd stage 25 tons.
    Thermostatic expansion valves and intertwined evaporator.

    unit sized for full capacity during occupied times but during unoccupied times
    unit maintains set point but has short run cycles, creating high humidity(>68%)
    positive building pressure has been verified.


    What would be the better option to control humidity ?

    1. Rawal device on 1st stage circuit ?
    2. Install vfd on evaporator motor and run preset speeds for 1st and 2nd stage cooling ?
    3. install controls to bang on electric heat strips for reheat control ?
    4. Hack in a hot gas reheat coil ?

    side note---- due to building and duct design there is no possible option to add a stand alone dehumidifier

    I'm game for any suggestions
    There are many ducted dehumidifier s that can be added to your ducts. Check out the Ultra-Aire XT 255.
    This will cut your electric bill hundreds of $ per month.
    It could take a couple units. They provide 30 gals. of moisture removal per day per unit while providing free reheat for $1 per hour per unit. Providing 50%RH in the space at 80^F requires much less moisture removal than by cooling to remove moisture that maintain <50%RH at 70-75^F.
    This is a no brainer for an unoccupied space like church that is unoccupied for most days and all evenings.
    Call Justin @ 800 533 7533 for further discussion or follow with post.
    Regards Teddy Bear
    Bear Rules: Keep our home <50% RH summer, controls mites/mold and very comfortable.
    Provide 60-100 cfm of fresh air when occupied to purge indoor pollutants and keep window dry during cold weather. T-stat setup/setback +8 hrs. saves energy
    Use +Merv 10 air filter. -Don't forget the "Golden Rule"

  12. #12
    Join Date
    Jul 2005
    Location
    south
    Posts
    641
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    Thread Starter
    Duct work under slab
    Unit sets on curb behind building
    No access to duct work for a stand alone humidifier

  13. #13
    Join Date
    Dec 2014
    Location
    midwest
    Posts
    1,574
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    Quote Originally Posted by heatingman View Post
    Yes. I have installed them. They work well if there sized properly - involve rawal in the selection, and it will work like a champ.

    Just add valving to close it off to check charge easier.

    Essentially what it does is add a secondary path for hot gas refrigerant to flow directly back to the compressor. There website explains in much better, but essentially the refrigerant flow to the evaporator gets reduced, so it slows down causing an increase in evaporating temperature- which is adjustable. This reduces evaporator capacity which allows for longer run times and as a byproduct better humidity control.


    Sent from my iPhone using Tapatalk
    I have not installed one, but have worked on a few, rebuilding etc, and they do work well.



    Sent from my SM-G930V using Tapatalk

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