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  1. #1
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    Sensible Cooling Question

    During the sensible cooling I understand that the dry bulb temperature goes down but I don't understand why the the wet bulb temperature also goes down? Can some one please explain in detail?
    Thanks

  2. #2
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    Aug 2014
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    Hi, Usa
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    Read this. Might help you to understand.

    This is not my article. I give Credit to the guys who wrote this.

    http://atsiteinc.com/wp-content/uplo...etBulbTemp.pdf

  3. #3
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    Thanks for that info but sorry I am still not clear as to why the wet bulb temp goes down during sensible cooling.
    Can anyone explain?
    Thanks

  4. #4
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    Visalia California 93291
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    Where are you measuring? In the space or after the coil?........There is Always some Latent being done which will lower WB......Lower RH = Lower WB

  5. #5
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    No I am not measuring anywhere. This is what I found online stating the sensible cooling lowers both db and wb temps. I am thing the sensible cooling should only lower the db.

  6. #6
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    I mean I am thinking that only the db temp should go down.

  7. #7
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    Quote Originally Posted by Bond007 View Post
    I mean I am thinking that only the db temp should go down.
    Nope...unless RH is @ 0% which is unlikely or your cooling coil is above dew point

  8. #8
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    Thanks for a quick reply. So why on the evaporative cooling the WB temp stays same and only DB temp goes down?
    Thanks

  9. #9
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    Your well above the Dew Point-- Actually the WB IS going down from the OSA temp from the Evaporation Effect that is cooling the air..the Space WB will actually go up a bit as you are adding moisture to the air- After that you are simply doing Air Changes with Already Cooled Air

  10. #10
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    Sep 2015
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    Your question Is a good one, but has no intuitive answer.

    Wet bulb is the temperature a thermometer with a soaked sock over the murcury bulb in a moving air stream reads. It is a measured value used to determine humidity ratio and related properties of moist air or psychrometrics. The relationship between wet bulb and dry bulb (no sock) is nonlinear. ASHRAE fundamentals manual devotes an entire chapter to psychrometrics and in the most recent version moved it to chapter 1. KW Engineering published a free Excel add-in for calculating psychrometric properties.

    Instead of seeking the specfic answer, I suggest plugging psychrometrics into Google and take a few hours to get the whole picture.

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  12. #11
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    As you follow a sensible heat line from right to left across the psychrometric chart, you can see that the relative humidity increases as the temperature decreases. This is because is because the specific humidity or "grains of moisture per pound of dry air" remains the same. Cooler air holds less moisture under these conditions than warm air. As the humidity increases there is less moisture evaporated from the gauze that is wrapped around the wet thermometer. As you move across the sensible heat line the wet bulb temp approaches the dew point temp until they are the same at the saturation line.

  13. Likes Sergey Tranes liked this post
  14. #12
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    online psychrometric calculator -- Tornado hvac-calculator.net

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