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  1. #1
    Join Date
    Jul 2006
    Location
    The Great country of Texas
    Posts
    429

    RTHB on Ice Storage

    This is going to be a long post but here it goes. I have to RTHB 300's on 14 Calamac ice tanks on a building. The glycol is set for 12 degrees. The chillers have the proper charge, tubes clean on both vessels, water flows are good and stable condenser water. Here is the problem. The chillers operate fine during the day in non-ice storage mode. All approaches are good an they maintain 35 degree leaving glycol. It all goes to hell in the ice mode on startup. Since these are RTHB's, they have the EXV that is controlled off of a discharge superheat algorithum built into the UCP2. The EMS sends the signal to built ice. The chiller forces the slide valve to full load for ice production. What is happening is the discharge gas temp. drops causing the exv to shut which in turn drives the evap temp down to 14 degrees tripping the chiller off on low evap temp. The chiller algorithium wants to maintain a calculated 35 degree superheat. The actual superheat will be around 20 degrees causing the exv to go to 0-1 % open, boom down goes the chiller on low evap temp. I have manually forced the exv to 30% on startup but you only get about 10 min to jack with it before it goes off on low discharge superheat but the evap temp be ok at this point. The superheat variable is built into the micro and can not be changed. I have jacked with the control algorithuim settings from 1 -4, no luck! Pueblo has never seen this and they are stumped. I even had a refrigerant sample done to see if there was excess oil in the refrigerant, came back good. I thought about putting a time delay on the load signal only when it goes into ice mode to see if the machine would stablize the exv as it loaded. Has anyone had this problem? It is pretty sad when you know what the problem is but don't know how to correct it! By the way, it also has the most current version software in the UCP 2. And no, changing the chiller is not an option although I wish it was a RTHA!
    "I'm from Texas, what country are you from?"

  2. #2
    Join Date
    Aug 2006
    Location
    Mixing oil and fire with a big spoon.
    Posts
    4,390
    well, here goes...

    rthb-sb-2. talks about upgrading the chips (i know that you say that you upgraded the software) but at the end of that bulletin, it talks about figuring out the proper charge and operation.

    you say that it trips at 14F sat evap, is it supposed to? i do not know what your glycol concentration/type is, but perhaps your trip point it supposed to be lower. perhaps not. just a thought. 14F trip equates to approx 22% glycol.

    your default "maximum travel setpoint" (maximum is closed, go figure) is 2500 steps...perhaps you can lower this setting (preventing the exv from completely closing). although this may cause some low discharge superheat issues.

    rthb-sb-6, the refrigerant charges have also been revised (depending on your date of manufacture) from the original IOM. they recommend a larger oil quantity of oil and a smaller refrigerant charge. a larger refrigerant charge can cause a low discharge superheat.

    let us know.
    good luck.
    When I am late for work, I usually make up for it by leaving early.

  3. #3
    Join Date
    Oct 2006
    Location
    Central Texas
    Posts
    634
    I don't know if this will help, 2500 steps for max exv is travel is down from 2760 on the 300 ton chillers. What is the exv closed stop set for? If at 0 % have you tried increasing this value to 3.5% so it will not close off completely, this could allow the algorithum to catch up. Just a thought.
    Sic Semper Tyrannis.

  4. #4
    Join Date
    Jul 2006
    Location
    The Great country of Texas
    Posts
    429
    I have played with the charge in the past. I have removed gas to make the exv go more open. It works but affects it on the normal run. I put a minimum in the exv, it will then cause low discharge superheat trip so it is a catch 22 situation.
    "I'm from Texas, what country are you from?"

  5. #5
    Join Date
    Jul 2006
    Location
    The Great country of Texas
    Posts
    429
    Jay, there is 25% glycol tested with a spectrometer. The chiller produces a leaving temp of 20-22 degrees. It will ride on evap limit around 16 dergrees and trip at 145
    "I'm from Texas, what country are you from?"

  6. #6
    Join Date
    Mar 2005
    Posts
    664
    sounds like need application adjusted in eeprom via factory , regards stan
    Keep it simple to keep it cool!

  7. #7
    Join Date
    Oct 2003
    Location
    tidewater, va
    Posts
    2,144
    Stickerhead,
    How is waterflow on this machine?


    r404a

  8. #8
    Join Date
    Jan 2004
    Posts
    1,176
    I believe that in ice mode, like extended unloading, it does not look at discharge superheat. The exv drives to open and stays there irregardless of discharge temp. The other thing you can do, judging by your glycol %, prolly 40% , is take that refrigerant temp from 15 deg to -10 deg or more.

  9. #9
    Join Date
    Jul 2006
    Location
    The Great country of Texas
    Posts
    429
    Water flow is good 30 to 22 degrees. No, the unit still looks at disc. gas superheat in ice mode to move the exv. FYI, it has had the eprom upgrade. We are going to re-look at the charge and check the speed of the slide valve. I did find out from Pueblo that the soft load (when activated) will soft load it in ice mode. Onec it is turned on, it works in both comfort and ice mode. Keep you posted!
    "I'm from Texas, what country are you from?"

  10. #10
    Join Date
    Jul 2006
    Location
    The Great country of Texas
    Posts
    429

    Update on ice storage

    Pueblo does not know their own chillers! RTHB in ice mode ignore soft load and leaving water temp. The only thing that will stop the chiller in ice building mode is low evap temp and overload. In ice building mode, the compressor does not unload except for high motor current. Balls to the walls! The way I corrected it was to take away the ice building mode and drop the leaving chilled water to 23 degrees. As long as you are in conventional cooling mode, all safety like low evap inhibit and low water temp come into effect that will unload the compressor as necessary. So far, we have built ice for two weeks with no problems with 23 to 24 degree leaving glycol.
    "I'm from Texas, what country are you from?"

  11. #11
    Join Date
    Jan 2004
    Posts
    1,176
    Huh, what do ya know, I know more than Pueblo.

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