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Thread: enthalpy exact calculation

  1. #1 enthalpy exact calculation 
    Forum Freshman
    Join Date
    Jun 2013
    Hello to all!

    I have a question regarding enthalpy calculation... I am trying to do some exergy analysis and I need to have exact enthalpy values... which values for cp,air cp,wv and r (h=cp,a*T+w(r+cp,wv*T)) do I need to use to get exact enthalpy values for moist air (compared to ashrae tables)? using suggested approximate values cp,air=1,006 co,wv=1,86 and r=2501 i get slightly different results than values in ashrae table - error is +/- 0,1 but this can result in a significant error in exergy efficiency in some cases (exergy efficiency larger than 1). I ruled out other possible causes for this...

    i tried to get polinomal equations for dry and saturated air enthalpy (form ashrae table) but i do not get good results with excel.. because i need to calculate a lot of different cases, calculating moist air enthalpy 'by hand' from ashrae tables would take A LOT of time...

    i hope i was cleat what i need to do


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  3. #2  
    Join Date
    Apr 2007
    Perhaps you could get an add-in for your spreadsheet which includes the properties from the ASHRAE tables, such as the following.

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  4. #3  
    Forum Freshman
    Join Date
    Jun 2013
    thank you for answering harold.

    unfortonately this add in is a bit expensive for me, so i am trying to find some other way...

    how could i get polynomials from tabled values without using excel? do you have maybe any other idea?

    thank you for help!
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