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  1. #1
    Join Date
    Apr 2008
    Location
    Louisiana
    Posts
    232

    Enthalpy formula

    Hi all. I'm new to this site and am working on an econmizer program today. Program is written in GCL. Does anyone now a formula to determine outdoor air enthalpy based on the inputs from an outdoor air temp sensor and outdoor air humidity sensor. Any help is appreciated.

  2. #2
    Join Date
    Dec 2002
    Location
    SouthEast NC ICW & Piedmont Foothills
    Posts
    7,619
    It`s better to be silent and thought the fool; than speak and remove all doubt.

  3. #3
    Join Date
    Nov 2007
    Posts
    388
    I have a paper from ASHRAE that you could use to derrive the equation....It is not pretty!!!!!I'll e-mail it too you if you want.

    You may be better off (less time & code debugging) buying a transmitter that outputs enthalpy...Vaisala is a good Mfr.http://www.vaisala.com/instruments/p...y/fixed/hmt330

  4. #4
    Join Date
    Feb 2005
    Location
    Where it's dark & damp
    Posts
    597
    Enthalpy = 8 + 0.27 * (Dry_Bulb - 35.0) + 0.5 * ((Dry_Bulb - 35.0) * (RH/100))
    Last edited by willf650; 04-05-2008 at 07:55 PM.

  5. #5
    Join Date
    Nov 2004
    Location
    SW FL
    Posts
    5,996
    Quote Originally Posted by GONFISHN View Post
    .. am working on an Economizer program today. Program is written in GCL.

    Does anyone now a formula to determine outdoor air enthalpy based on the inputs from an outdoor air temp sensor and outdoor air humidity sensor.

    Any help is appreciated.
    You can discover accuracy of formula offered by Willf650 through testing.
    +++
    I guess you can review ParksSoft Online, purchase or
    discuss by sending email to Bob Parks

    support _at_ parkssoft _dot_ com

    Parks Software
    P.O. Box 162
    Gradyville PA 19039

    Add comparison


    35 EZ Air 8 + 0.27* (DB-35) +0.5 ((DB-35)*RH/100))
    DB DB - 35 WB RH CALC Formula Difference
    1

    95 _ 60 82 _ 58.0 __ 45.64 41.60 __ 4.04
    90 _ 55 80 _ 65.1 __ 43.47 40.75 __ 2.72
    85 _ 50 75 _ 63.3 __ 38.42 37.33 __ 1.10
    80 _ 45 70 _ 61.2 __ 33.93 33.92 __ 0.01
    75 _ 40 65 _ 58.8 __ 29.93 30.56 __ -0.63
    70 _ 35 60 _ 56.1 __ 26.35 27.27 __ -0.92
    65 _ 30 55 _ 52.8 __ 23.13 24.02 __ -0.89
    60 _ 25 50 _ 48.9 __ 20.22 20.86 __ -0.64
    55 _ 20 45 _ 44.3 __ 17.59 17.83 __ -0.24
    50 _ 15 40 _ 38.8 __ 15.19 14.96 __ 0.23
    45 _ 10 35 _ 32.2 __ 12.98 12.31 __ 0.67
    40 _ 5 30 _ 23.4 __ 10.90 9.94 __ 0.97
    35 _ 0 25 _ 11.7 __ 8.93 8.00 __ 0.93
    Last edited by dan sw fl; 04-06-2008 at 09:16 AM. Reason: Comparison
    Designer Dan
    It's Not Rocket Science, But It is SCIENCE with "Some Art". ___ ___ K EEP I T S IMPLE & S INCERE

    Define the Building Envelope and Perform a Detailed Load Calc: It's ALL About Windows and Make-up Air Requirements. Know Your Equipment Capabilities

  6. #6
    Join Date
    Aug 2006
    Location
    Wisconsin
    Posts
    26

    ACI Enthalpy transmitter

    ACI also carries Enthalpy Transmitters with considerations for Elevation

    http://www.workaci.com/pdf/Humidity/...an.pdf#zoom=80
    Enjoy your day!

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