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Thread: Enthalpy

  1. #1
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    working in HVAC feild more than 14 years as technician, never had to deal with Psychrometric Chart, ( well thats how we worked in Middle east) recently moved to UK, plus developed interest in theory of HVAC, start reading related books. I do feel lost some time when i try to learn on my own from books, like now, i have under stood say about 70% or more of Psychrometric chart and can use it too, what confusing me is The word ENTHALPY, dictionary tells me its meaning as THERMODYNAMIC QUANTITY EQUIVALENT TO THE TOTAL HEAT CONTENT OF A SYSTEM. some one please explain what that means, if you can give couple of examples that will greatly help. thanks

    [Edited by anisaamm on 12-15-2005 at 07:26 AM]

  2. #2
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    Enthalpy is a measure of total heat content of outdoor air, and considers humidity as well as temperature. Temperature is measured by an adjustable tstat called an outdoor air thermostat or OAT. Enthalpy is measured by an adjustable device call the Enthalpy Control or EC.

    More effective use of outdoor air can be made if we consider a total heat content instead of just its drybulb temperature. This can be done by using an Enthalpy Control instead of an Outdoor Air Thermostat.
    To put the world in order, we must first put the nation in order; to put the nation in order, we must put the family in order; to put the family in order, we must cultivate our personal life; and to cultivate our personal life, we must first set our hearts right.
    -- Confucius

  3. #3
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    Anthalpy

    Thanks for your help, would u please give a couple of example linking enthalpy with rest of phsychrometric chart, or its applications

  4. #4
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    enthalpy of saturation

    for instant rnthalpy of saturation, BTU per pounf of air, kindly explain

  5. #5
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    Re: Anthalpy

    Originally posted by anisaamm
    Thanks for your help, would u please give a couple of example linking enthalpy with rest of phsychrometric chart, or its applications
    The EC senses both temp. and humidity. The EC has four fixed positions A B C D. Each setting defines a range of conditions at which the control will operate. The operating ranges can be better visualized if you look at a psychrometric chart. you can look at the shape of the bands and tell that as humidity decreases the allowable temperature for free cooling increases, which is why Enthalpy is a better measure of suitability than temperature alone.

    My email is in my profile. I can send you a jpeg with the info.
    To put the world in order, we must first put the nation in order; to put the nation in order, we must put the family in order; to put the family in order, we must cultivate our personal life; and to cultivate our personal life, we must first set our hearts right.
    -- Confucius

  6. #6
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    As coolwhip has been explaining it is the total heat content of the air. When you sensibly/cool heat moist air or change the amount of moisture in the air you are changing the enthalpy

    It compares the total heat to the air to a reference point. For easy math they sometimes base it on 0 degrees F.

    On a 'per pound of dry air basis', it is the sum of the specific heat of air times the temperature increase above 0F, the latent heat to evaporate the mositure content( moisture per pound of dry air), and the specific heat of the water vapour(moisture per pound of dry air) times the temperature increase above 0F.
    The way we build has a greater impact on our comfort, energy consumption and IAQ than any HVAC system we install.

    http://www.ductstrap.com/

  7. #7
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    Crap! Hope those pegs were ok. My scanner is on the fritz again.
    To put the world in order, we must first put the nation in order; to put the nation in order, we must put the family in order; to put the family in order, we must cultivate our personal life; and to cultivate our personal life, we must first set our hearts right.
    -- Confucius

  8. #8
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    In SI they will sometimes base it on 0 degrees C, on a 'per kg of dry air' basis. The specific heat increases above 0C.
    The way we build has a greater impact on our comfort, energy consumption and IAQ than any HVAC system we install.

    http://www.ductstrap.com/

  9. #9
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    Smile entholpy

    Great to see a person that is interested in the science of the trade. Don’t for get the word Latent. Aren’t we basically talking about state change, like when the body creates water on our skin for a state change to take place (saturated liquid put in to an evaporator to boil) to lower our body temp. Where is John D. when you need him? This thread could go longer then the Serverroomcooler theard.
    Got to run.

    Cvw

    I know enough to be dangerous


    [Edited by cvw on 12-15-2005 at 01:22 PM]

  10. #10
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    Norm Chris could really enlighten you, ooohhh Norm ????
    Da Threadkilla

  11. #11
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  12. #12
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    Very nice!!!
    To put the world in order, we must first put the nation in order; to put the nation in order, we must put the family in order; to put the family in order, we must cultivate our personal life; and to cultivate our personal life, we must first set our hearts right.
    -- Confucius

  13. #13
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    yes thats a good link.

    another is the "gray manual" from the honeywell site
    I dont have the link,but I will try to help find it if need be.

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