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  1. #1
    Join Date
    Aug 2003
    Posts
    35
    A customer of ours has twin York Chillers YCWS0140 and BAC towers VT0-132-LD. The System orginally had Trane Chillers until lightning had its way with them. The system was using an economiser system which would use tower water under 45 degrees, through a heat exchanger to provide cooling. The heat exchanger system from what I was told never really worked that well and they abandoned it when the chillers were changed and had a controls upfit.
    The problem is now when the water gets below 70 degrees the chillers lock ou on low oil pressure differential due to the pressures running too low. I think the Trane systems used hot gas bypass to eliviate this. The Yorks don't have HGBP.
    My question is what is the best way to control the low end tower water temp to control head pressure? HGBP? Condenser water valve with head pressure control? Recirculation loop? Thanks

  2. #2
    Join Date
    Jul 2005
    Posts
    947
    Modulate tower dampers/ spray pumps/ fans?

  3. #3
    Join Date
    Jan 2002
    Posts
    254
    I think the best way is a tower bypass, but if you don't have one it's an expensive change. Usually the easiest is to add a HPCV on the leaving side of the chiller. Most have a main valve with a smaller in bypass across the larger for greater control purposes. If you have the plate frame you should still economize, there really is no reason to turn your back on free cooling if its available unless you have some special requirements. The chiller should be off until around 50-55 deg. OAT.
    Two wire hook up, three wire f**k up.

  4. #4
    Join Date
    Aug 2003
    Posts
    35
    The problem is the Chiller spec's says it is to have 70-75 degree water for condenser cooling. Anything under that and it makes problems.

  5. #5
    Join Date
    Nov 2005
    Location
    Texas
    Posts
    1,628

    Drive


    Maybe a VFD on Tower Fan?


    Regards........

  6. #6
    Join Date
    Aug 2003
    Posts
    1,311
    agree with gonefishing, look for a way to modulate the tower capacity.

  7. #7
    Join Date
    Oct 2001
    Posts
    6,966

    Hmm

    how about piping hot water to the heat X and heating up the tower troth to say 70f the other way,or limit the chiller on start-up(slow load up)and let it heat the water with the tower fan off till 75F-85F for the winter.
    "when in doubt...jump it out" http://www.youtube.com/watch?v=U1qEZHhJubY

  8. #8
    Join Date
    Nov 2005
    Location
    nashville,tn
    Posts
    9
    diverting valve, requires repiping and adding the modulating valve, controller, wells,etc installed on a couple of 23xl carriers took care of problems

  9. #9
    Join Date
    Jun 2005
    Location
    Ohio
    Posts
    1,720
    The tower fan control should be set above 75* so it should be off, A tower bypass is good but pricey. It is only good if you've got a load(enough heat to keep the tower water warm). We've got a 400 ton screw with a condensor water holdback valve on the condensor outlet. If you go that route, don't forget to set it so the valve can only close 75-80%, always keeping a little flow thru the condensor. Ours is controlled off of discharge pressure.
    Jogas

  10. #10
    Join Date
    Nov 2005
    Location
    nashville,tn
    Posts
    9
    jogas is correct on all factors, i believe either option is your answer

  11. #11
    Join Date
    Aug 2003
    Location
    Fort Worth, TX
    Posts
    11,346
    We have the whole shootin' match at our facility; towers with sump heaters, VFD drives for the fans, and tower water bypass on a PID loop tied to our Metasys. We were down to 15 degrees outdoor ambient last week and the one 19XR chiller online didn't miss a beat. Chiller has to run 24/7/365 due to nature of facility.

    During low ambients the VFD's will ramp down to 20 HZ (minimum) and the bypass takes over from there...have yet to see it go beyond 50% bypass...there's a decent load on the chiller even in winter. Chilly mornings make for cool looking clouds wafting up from the plant's towers.
    • Electricity makes refrigeration happen.
    • Refrigeration makes the HVAC psychrometric process happen.
    • HVAC pyschrometrics is what makes indoor human comfort happen...IF the ducts AND the building envelope cooperate.


    A building is NOT beautiful unless it is also comfortable.

  12. #12
    Join Date
    Aug 2003
    Posts
    35
    Yes the fan is set to come on at 80. The low temp is the one we are having the problem controlling. Looking at the book from the old chillers the only thing I saw that was quite different, was that the Tranes had hot gas bypass. I didn't see any type of water contol valves in the prints or in the unit documentation. Maybe it didn't cause any problems with those chillers. I wouldn't think that HGBP would be a good choice of control for this problem????

  13. #13
    Join Date
    Mar 2005
    Location
    Virginia
    Posts
    1,144
    VFD on the open loop pump, and program properly.

    or

    As jogas mentioned.


    Not knowing the price of jogas's idea I dont know which would be easier/cost effective.

    [Edited by codewriter on 12-16-2005 at 11:19 PM]

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