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  1. #1
    Join Date
    Apr 2004
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    Pakistan
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    leaving dry and wet bulb difference of Evaporator coil



    One of the enquiries from the consultant came 2 me for DX coil

    Conditions were

    Air IN 87.7F/59.2F (DB/WB)
    Leaving 59.3F/47.5F (DB/WB)
    CFM 5000
    Capacity 153000BTU/hr

    I am confused over the difference in DB and WB of leaving temperature Is it POSSIBLE?


    Our nose is our personal air-conditioning system: it warms cold air, cools hot air and filters impurities

  2. #2
    Join Date
    May 2005
    Location
    Australia
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    83
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    19

    Re: leaving dry and wet bulb difference of Evaporator coil

    for the figures you gave you would get:
    Sensible heat load = 153,610.1 BTU
    Latent Heat Load = -6255.5 BTU
    Total Heat Load = 147,354.7 BTU
    I would suspect the readings as you have negative latent heat..in other words the evap is giving up latent heat......
    100% is possible 100% of the time

  3. #3
    Join Date
    May 2005
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    Australia
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    Re: leaving dry and wet bulb difference of Evaporator coil

    For your air in/out you have:
    air in air out
    Dew point = 34.8F 35F
    RH = 15.2% 40%
    H/Ratio w .00422lb water/lb dry air .00427
    H/R g 29.6 grains 29.9g
    SV 13.833 cu ft/lb 13.174
    Enthalpy 25.69BTU/lb 18.87

    Hope these mean something to you.....
    100% is possible 100% of the time

  4. #4
    Join Date
    Apr 2004
    Location
    Pakistan
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    Re: leaving dry and wet bulb difference of Evaporator coil

    tell u what guys i think it is dry surface cooling.

    My question was how does this happen.


    I know how 2 select the coil. you may see the attachment.
    Attached Images Attached Images
    Our nose is our personal air-conditioning system: it warms cold air, cools hot air and filters impurities

  5. #5
    Join Date
    Apr 2001
    Location
    New Port Richey, Florida - USA
    Age
    78
    Posts
    5,072
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    34

    Re: leaving dry and wet bulb difference of Evaporator coil

    Seems pretty straightforward to me. The entering dewpoint is about 35F. Dew (moisture) is only going to condense on a surface that is colder than dewpoint. The coil surface was not cold enough to extract moisture, therefore you have a dry coil.

    The leaving air, not having lost any moisture, still has a dewpoint of about 35F.

    34.8 vs 35 is instrument error.
    Last edited by Gary; 10-06-2005 at 12:28 AM.

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