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Dehumidify and control cooilng temperature

Hello,



I'm developing a software to control a simple air handling unit (ahu)







My goal is to control the temperature & humidity with a cooling and a heating coil.







Right now, I'm controlling the temperature easily, but I can't control the humidity at the same time !







With a web research, I think I have to produce more cooling capacity and

the reheat the air with the cooling coil , but I can't find a relation

between how much I have to cool and how much I wan't to reheat to

maintain the relative humidity between 50-60% RH !







I would appreciate any help since my area is electronics !

Comments

  • Empire_2
    Empire_2 Member Posts: 2,343
    Sounds like an indoor pool unit.

    Heating and cooling loads should be calculated and they should be enough to either heat or cool the room.  Ideally if your main concern is to dehumidify the structure with an A/C unit with an internal condensing coil and with a remote condenser for heat rejection.  Check out Dectron.com.  The idea behind internal condenser is to drop RH% and at the same time keeping the heat inside the structure.  If the structure becomes too warm, we can reject heat load to the outside.  In this case the heat may or may not come on to keep temp.,...Sometimes staged for lo and hi heat depending on application.



    Peace;



    Mike T.
  • iJAF
    iJAF Member Posts: 2
    Ahu

    No this is for a air handling unit !
  • bob_46
    bob_46 Member Posts: 813
    Psychometrics

    Google psychometrics. You need a basic understanding of the psychometric chart and the condition of the air entering the air handler .
    bob
  • Mark Eatherton
    Mark Eatherton Member Posts: 5,837
    bob, you're missing an r there...

    I believe you meant psychRometrics, also known as hydrometry.



    Psychometrics is a whole 'nother subject ;-)



    ME
    It's not so much a case of "You got what you paid for", as it is a matter of "You DIDN'T get what you DIDN'T pay for, and you're NOT going to get what you thought you were in the way of comfort". Borrowed from Heatboy.
  • bob_46
    bob_46 Member Posts: 813
    Psychometrics

    So much for spell check. I had it right but the computer said I was wrong > Then again I might have been thinking about all the news from Aurora.
    bob
  • Mark Eatherton
    Mark Eatherton Member Posts: 5,837
    Eye haight spill czech...

    I keep it turned off on all my equipment ;-)



    Can ewe tell?



    ME
    It's not so much a case of "You got what you paid for", as it is a matter of "You DIDN'T get what you DIDN'T pay for, and you're NOT going to get what you thought you were in the way of comfort". Borrowed from Heatboy.
  • Jean-David Beyer
    Jean-David Beyer Member Posts: 2,666
    Psychometrics is a whole 'nother subject ;-)

    It sure is!



    There is a cute book called "The Clairvoyant Countess" about a woman (who really was a countess) who practiced psychometry. [My spelling checker will not take that.] Whether you believe in it of not, it is a nice read. By Dorothy Gilman.



    http://www.amazon.com/Clairvoyant-Countess-Dorothy-Gilman/dp/0449213188/ref=sr_1_1?s=books&ie=UTF8&qid=1343240374&sr=1-1



    Let's see if my spell checker will take what he meant. psychrometry . Nope Psychrometer Nope.
  • Empire_2
    Empire_2 Member Posts: 2,343
    OK basic AHU and obtainable RH%.

    There is nothing special about this system nor the program software you are trying to develop.  50%-60%RH is easily obtainable with bare bones equipment and environment.  The only concern would be summer/winter operation.  I can lower the RH by cooling the envelope and maintain the temp by energising the heat to maintain temp.  Stages can be added to better control the rate at which the envelope reheats so over shot don't happen.  This example is for summer operation,...Winter if applicable will need additional equipment to add Humidity if needed.  Not really sure what the special request is, but RH% does not seem to be critical to warrant any psychrometrics concern.  Again 50 to 60RH% is easily obtainable.  Am I missing something?  It's not an indoor pool, nor a Laboratory......Perhaps something that is critical for expensive wood products like Grand Piano's of age?  Is cost an issue or is it at any cost?  Help me out here if possible.  I think to answer the last part of you Q:? The structure/envelope/room,....not sure which, heat and cool requirements must be able to cover the load.  The equipment has more than enough potential to cover this small request of 50-60RH% @60 to 90* f. 



    Peace

    \

    Mike T.



    Mike T.
This discussion has been closed.