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  1. #1
    Join Date
    Jan 2006
    Posts
    17

    reverse engineering help

    Hi all.....

    I am a Mech Eng with no HVAC experience, but have been asked to help with a 25yr old Glycol chiller. System has been "badgered" over the years, and documumentation is almost non existant. I have been trying to reverse engineer the thing, but have a few questions. First - what I do know:

    Continental NUPAC air cooled chiller (w remote condenser)
    9 ton (nominal) capacity
    R134a
    fluid: 40% EG
    flow rate: 50gpm
    Ent temp: 15 deg F
    Lvg temp: 10 deg F
    Ambient Temp: 65 deg F

    OPTIONS:
    Low Ambient to -20 deg F
    hot gas bypass
    suction accumulator
    oil seperator
    head pressure control + 2 speed condenser fan

    My first thought was to get into the pressure enthalpy diagram. Is a good assumption for the design high pressure side to be:

    65 + 30 = 95 deg F - corresponds to 129 psia

    What is a good assumption for the low pressure side design temp/pressure? Would it be 10 deg F (leaving glycol) minus some standard # for the evaporator?

    I have dug up alot of information on all of the individual components in the system. Just not the "nominal" operating conditions. Any suggestions or help with a "plan of attack" would be much appreciated....

    Just FYI - the system is not meeting spec, and I have been asked if I can figure out why not.

  2. #2
    Join Date
    Sep 2002
    Location
    Hampton Roads, Virginia
    Posts
    1,596
    Quote Originally Posted by hvacer2 View Post
    Hi all.....


    Continental NUPAC air cooled chiller (w remote condenser)
    9 ton (nominal) capacity
    R134a
    fluid: 40% EG
    flow rate: 50gpm
    Ent temp: 15 deg F
    Lvg temp: 10 deg F
    Ambient Temp: 65 deg F
    Are these the specs. or the present operating conditions ?
    "Profit is not the legitimate purpose of business. The legitimate purpose of business is to provide a product or service that people need and do it so well that it's profitable."

    James Rouse

  3. #3
    Join Date
    Jan 2006
    Posts
    17
    these are numbers i found on an old spec sheet......

  4. #4
    Join Date
    Jul 2000
    Location
    Dallas,Texas
    Posts
    4,948
    klrogers is asking a good question. At first glance your GPM is way high.

  5. #5
    Join Date
    Mar 2008
    Location
    Indy
    Posts
    354
    I would need more info on the refrigeration circuit to be certain. Pressures, superheat, subcooling, etc...
    I would probably take a close look at a 25 year old chiller using 134a. I don't remember 134a being used until the early 90's.

  6. #6
    Join Date
    Jan 2006
    Posts
    17
    50 gpm was the spec....

    I have measured (with several different methods) and get numbers in the mid 40s...

    If I am not mistaken, 50gpm x delta 5 deg F x S.H. of EG is approx 9 ton

  7. #7
    Join Date
    Jan 2006
    Posts
    17
    ahhh yes... my first small victory!

    when I was handed the folder, I was told "25yr old system". I just looked at the date on the original spec sheet and see it was built in 93.

    Sorry - my bad.

    As for Pressures, superheats, subcooling, - well, these are what I am trying to figure out (well - at least what they should be).

    The only thing I could find was that the TXV was set at 13 deg F (factory). The system has a reciever in it if that helps (subcooling wise).

  8. #8
    Join Date
    Jul 2000
    Location
    Dallas,Texas
    Posts
    4,948
    ..
    Last edited by wolfdog; 04-16-2008 at 11:11 PM.

  9. #9
    Join Date
    Mar 2008
    Location
    Indy
    Posts
    354
    Unless I can put my hands on it, I'm usually no help. Try here http://www.air-conditioning-and-refr...d-chiller.html

  10. #10
    Join Date
    Apr 2004
    Location
    Rossville, GA
    Posts
    104
    Evaporator approach defined is 10 degrees colder than your leaving medium. Have you checked the specific gravity of EG? Is this system capable of running? If so we would need more trends.

  11. #11
    Join Date
    Jul 2000
    Location
    Dallas,Texas
    Posts
    4,948
    If you are looking for Continental chillers....http://www.continentalteam.com/index.html

    If they are like some other process chiller manuf. they will have a file on the original design/build for this one.

  12. #12
    Join Date
    Jan 2006
    Posts
    17
    The system produces chilled glycol at ~45gpm right now..... That glycol is pumped to three seperate circuits. Two of them have AHUs and the third is to pipes embedded in the floors and walls.

    The glycol flow is not really the problem (I don't think). The chiller does not seem to be able to get down to the specified temperatures (even when removing much less than 9 tons).

  13. #13
    Join Date
    Nov 2002
    Location
    NJ - WORK IN NYC AREA
    Posts
    1,434

    Question

    Please correct me if I'm mistaken, but due to the weight of the glcol solution you need a higher flow rate than the 2.4 gpm for water.

    You said the system is 25 years old. What is the present condition of the solution?? Has it been chemically maintained over the years? If not, you may be pumping more of a jel than a solution? You may not get the heat transfer you should be getting.
    "My hands are for sale"

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