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  1. #1
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    Apparatus Dew Point

    Hi, i'm new to this forum as well as this industry. Just out of grad school i've joined this HVAC contracting firm and have a lot of unanswered questions. To start with about the psychrometric charts....

    Suppose i have outside air conditions of 80*f DB and 70*f WB / indoor conditions needed are 56*f DB and 55*f WB. How do i know the Apparatus dew point from the chart?

  2. #2
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    Lancaster PA
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    Right side of chart has dew point.
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  3. #3
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    Fort Worth, TX
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    Quote Originally Posted by BengalCooled View Post
    Hi, i'm new to this forum as well as this industry. Just out of grad school i've joined this HVAC contracting firm and have a lot of unanswered questions. To start with about the psychrometric charts....

    Suppose i have outside air conditions of 80*f DB and 70*f WB / indoor conditions needed are 56*f DB and 55*f WB. How do i know the Apparatus dew point from the chart?
    First of all, let's see if you understand what the apparatus dew point is. The numbers you gave for the indoor conditions sound like discharge air conditions, not indoor environmental conditions. At 56^F DB, 55^WB, the relative humidity is ~94%. These are not human comfort conditions.

    Apparatus dew point (ADP) is the dew point temperature of the cooling coil, which should be below the dew point of the return air entering the cooling coil. To determine ADP, you can use the psychrometric chart. Establish your return and supply statepoints on the chart, then draw a straight line through both points until it hits the saturation curve (the "instep") on the left side of the chart. Mark where it hits the curve, that's the ADP. It will typically be below the discharge air temperature.

    ADP is also known as Effective Coil Temperature (ECT). The dew point and the sensible temperature are the same, since ADP/ECT represents the moisture in the air being in a saturated state. ECT/ADP is useful for calculating coil bypass factor, to see to what extent air passing over the coil is left unaffected by the cooling coil.

  4. #4
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    Maybe he's ripening bannas with 100% outdoor air, so they can call them fresh ripened.
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  5. #5
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    Quote Originally Posted by beenthere View Post
    Maybe he's ripening bannas with 100% outdoor air, so they can call them fresh ripened.
    he he thanks it was just a problem i was solving, not allowed to handle real life situations yet.
    By the way i checked and found the 80,70*f has 94 gr/lb of moisture while the 56,55*f had 64 gr/lb of moisture. Though the relative humidity % is increasing the total moisture content is decreasing. Won't it be comfortable?????
    Last edited by BengalCooled; 07-18-2008 at 12:23 AM. Reason: grammar

  6. #6
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    No, the 55,56, is 94 or 95% RH, it would be a sweat box in that eviroment. Your body can't cool down by persperation, it it can't evaporate
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  7. #7
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    Quote Originally Posted by BengalCooled View Post
    he he thanks it was just a problem i was solving, not allowed to handle real life situations yet.
    By the way i checked and found the 80,70*f has 94 gr/lb of moisture while the 56,55*f had 64 gr/lb of moisture. Though the relative humidity % is increasing the total moisture content is decreasing. Won't it be comfortable?????
    Imagine being outside on a foggy day at 55^F with nothing on but a t-shirt, cargo shorts, and flip flops.

    Comfortable? I think not.

  8. #8
    Join Date
    Jul 2008
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    Bangalore, India
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    13

    thanks a ton

    Got it thanks people................

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