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  1. #1

    Enthalpy conversion btu/lb to kj/kg

    Can someone explain the conversion of enthalpy from btu/lb to kj/kg?

    Every website I search says to multiply by 2.326, but when I do some checks (using web based calculator or psychrometric charts) the results do not work.

    For example;
    77F, 50%RH = 29.3 btu/lb
    25C (i.e. 77F) 50%RH= 50.29 kj/kg
    and 29.3 x 2.326 <> 50.29!

    I am using an Alerton system which has an Enthalpy block which only supports F and btu/lb and I am working in SI (metric) units.

  2. #2
    Join Date
    Apr 2007
    Location
    San Diego, CA
    Posts
    1,302
    1 Btu/lb = 2.326 kJ/kg
    http://www.engineeringtoolbox.com/un..._per_unit_mass

    Not sure where you're getting 50.29 from.

  3. #3
    Information required for proper conversion is 1 calorie is heat reqquired to raise 1 gram of water by 1 Deg C and 1 BTU is amount of heat require to raie 1 LB of water by 1 deg F . 1 calorie = 4.187 Joule . 1 Deg F = (9/5 C ) + 32. All this information gives all information to think upon.

  4. #4
    Information required for proper conversion is 1 calorie is heat reqquired to raise 1 gram of water by 1 Deg C and 1 BTU is amount of heat require to raie 1 LB of water by 1 deg F . 1 calorie = 4.187 Joule . 1 Deg F = (9/5 C ) + 32. All this information gives all information to think upon.

  5. #5
    Join Date
    Oct 2002
    Posts
    77
    Quote Originally Posted by integrationx View Post
    Can someone explain the conversion of enthalpy from btu/lb to kj/kg?

    Every website I search says to multiply by 2.326, but when I do some checks (using web based calculator or psychrometric charts) the results do not work.

    For example;
    77F, 50%RH = 29.3 btu/lb
    25C (i.e. 77F) 50%RH= 50.29 kj/kg
    and 29.3 x 2.326 <> 50.29!

    I am using an Alerton system which has an Enthalpy block which only supports F and btu/lb and I am working in SI (metric) units.
    That's a good question. Luckily for me, when I've done work where they use SI, they're still OK with BTU/LB. This explains it though. "You can not convert from metric to imperial enthalpy or vice versa directly."

  6. #6
    Join Date
    Sep 2004
    Location
    SoCal
    Posts
    445
    forget osa/ra enthalpy comparison for economizer control

    small difference in rh/temp accuracy equals large energy/capacity loss

    better to use dewpoint transmitter from rotronics or airtest

    open economizer only if,
    osa db temp is < 72 F AND
    call for cooling is present AND
    osa dewpoint is < than 52.5 F

    cheers
    lb

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