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  1. #1
    Join Date
    Feb 2005
    Posts
    68
    Infinity heat pump system only comes in 1 ton steps.
    Would it be better to be a little under or little over in size.
    Looks like 23% under or 15% over going by Dash's calculations between 3 ton or 4 ton unit

    Load calc. by Flajoker's ac man came up to 33000.. spec used 95 degrees outside and 73 degrees inside.
    I do like to keep it at 70-72 in summer..maybe with the dehumidfy Flajoker won't need to go so low.
    relative hunidity is 84 day, 61 night on gulf coast

    Dash's words of wisdom in quotes (Flajoker copied from another post)
    "Quick answer."

    "Take a typical ton,26,800 sensible and 7,200 btus latent,total 34,000 btus."

    "Read the fine print of mfrs rating,rated at 80F indoor(return) air,deduct 835 btus ,per 1000 cfms ,for every degree below 80."

    Flajoker asks(Is there a web page with the mfrs fine print on it? Why do they only rate unit to cool to 80 degrees? Why does it loose capacity below 80 degrees?)
    Do they have a high number for heat as well?

    "So 1200 cfms,equals 1.2 X835 btus X 8 below 80=8016 btus to deduct ,from rated capacity."

    Flajoker says(I have no idea what the above means or how you got it. Could you please explain where cfms number comes from"

    "So deduct 8016 sensible btus,and a 3 ton is too small."

    "Check detailed cooling charts,most will have a nominal 3 ton that will handle it,but not if you want 72 in cooling,75 maybe"
    Flajoker could not find chart on web.

    This is amazingly interesting and informative.
    I have a new found respect for Hvac trade and work involved in getting it right.
    Thanks everyone for their comments and help

  2. #2
    If it truly has good capacity control,then I would go higher.

  3. #3
    Join Date
    Feb 2005
    Location
    Dothan, Al
    Posts
    3,453

    flajoker

    As iI stated inprevious posts.
    If you want thermostat below 75, go with lager unit.
    Either way, infinity will cost you more than you get back.

  4. #4
    Join Date
    Aug 2002
    Location
    Office and warehouse in both Crystal River & New Port Richey ,FL
    Posts
    18,836
    4 tons is probably the better choice,due to wanting 72F indoors.You will likely run it at a higher temperature ,with the lower humidity.Most of our customers find they need to rasie the set point,2 to 3.


    Why rated at 80 F indoors,not sure,guess it's becase they "always did it that way".Maybe someone can tell us all why.


    Don't know if you can find 80 reference on the web,but it's in all the hard data that I have,for several brands,It's "standard ARI conditions".In Florida normal design is 78 indoors,so the reduction is small enough,that it can usually be ignored.Problems sart when the owner wants less than 78F.


    The 835 btus of sensible reduction,per 1000cfms,is the rule.I'm not an engineer ,so I don't think I can explain the "why".I can tell you that I have seen what happens,if this is ignored,and incurred the cost of making that mistake.

    It's per 1000 cfms,so 1200 divided by a 1000 is 1.2,then times the 835 btus,then times thenumber of degrees below,80 F.Then deduct the total from the sensible btus given at 80F.

    We had 26,800 of sensible,after -8016,we have only 18784 btus of sensible,not enough to cool the home.We need to do the same calculations on a larger system,it will likely take a 4 ton.

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