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  1. #1
    Join Date
    Dec 2005
    Location
    Melbourne, Australia
    Posts
    98

    RTHB low refrig fault

    Hi Guys,
    Posted this one a while ago. Went through all the checks of refrig, oil and eprom upgrades as per bulletins. Trane: RTHB150ULFOONWR / Ser: U97CO9777. Obviously a 1997 model, so no adjustments are required on the refrig and oil charge.
    Found refrig leak on liq line refrig filter element connection. Removed all refrig, found 65kgs short, total should be 285lbs (130kgs). Replaced oil filter and the refrig filter element (Part No: FLR 03018) Original filter I removed was P/No: FLR 0860. According to Trane spare parts (Dalkia) here in Melbourne the 03018 is the replacement for the 0860. Would anyone know if this is correct? It took them three attempts to finally send me the correct one (I hope).
    Once correct amount of refrigerant was weighed in, started chiller. Have had constant faults of low refrigerant temp. Some days it can run for a few hrs, before failing. Have removed and checked all sensors, voltage and resistances, all o.k. Discharge superheat will read extremely low, so EXV closes down, even to 0% sometimes. Have even tried removing 5kgs, tested, then other 5kg of refrigerant. Did run alot better for a while, with disch superheat maintaining control set point and Exv sitting around the 15-20% open. After a few days, started failing again on low refrig temp. See details:
    Evap press:412kpa, disch:1256 kpa, Sat evap refrig temp:0.7 degrees C, sat cond temp: 34.9 , comp discharge temp: 52.7 , disch s/heat: 16.9 , disch s/heat control set point: 22.6 , EXV open %: 9.3 , steps open: 156 , evap approach: 5.7 , cond approach: 1.2 , evap ch water ent: 10 degrees C , evap ch w leave: 6.6 , cond water ent: 27.1 , cond water leave: 33.2.
    The condenser water uses only a throttling valve, no by-pass at c.tower, which is controlled by a separate siemens controller that someone has fitted in the past. This controller reads the system discharge pressure which drives the throttling valve.
    Would it be better for the chiller to operate this throttling valve? Would this set up be causing problems trying to maintain the discharge superheat setting? Maybe the chiller thinks it is still driving the throttling valve, but making no effect in raising the condenser water / discharge superheat temp, therefore using the EXV instead?
    Would anyone have any other ideas about this headache I have? Would be greatly appreciated. Cheers.

  2. #2
    Join Date
    Aug 2006
    Location
    Mixing oil and fire with a big spoon.
    Posts
    4,263
    for those of us who are metrically challenged...

    Evap press:412kpa (59.8 psig), disch:1256 kpa (182 psig), Sat evap refrig temp:0.7 degrees C (33.3F), sat cond temp: 34.9 (94.8F), comp discharge temp: 52.7 (126.9F), disch s/heat: 16.9 (30.4F), disch s/heat control set point: 22.6 (40.7), EXV open %: 9.3 , steps open: 156 , evap approach: 5.7 (10.3F), cond approach: 1.2 (2.2F), evap ch water ent: 10 degrees C (50.0F), evap ch w leave: 6.6 (43.9F), cond water ent: 27.1 (80.8F), cond water leave: 33.2 (91.8F).

    first off, your evaporator approach seems high at 5.7C (10.3F) but considering that your exv is only open 9% it may be ok, however, your load seems high at 3.4C (6.1F) chilled water temperature drop for only 9% exv...were these readings stabile? %RLA?

    chilled water or chilled glycol? and % and type if glycol.

    and ALWAYS suspect the BAS to be screwing things up when you aren't there!
    my 1st time jumping out of a plane...http://youtu.be/Kv38G0MHsGo

  3. #3
    Join Date
    Dec 2010
    Location
    Central US
    Posts
    412
    Just curious when you say throttling valve 2-way modulating on the condenser inlet/outlet of chiller?

  4. #4
    Join Date
    Sep 2008
    Location
    A land down under
    Posts
    306
    Quote Originally Posted by chill bill View Post
    Hi Guys,
    Posted this one a while ago. Went through all the checks of refrig, oil and eprom upgrades as per bulletins. Trane: RTHB150ULFOONWR / Ser: U97CO9777. Obviously a 1997 model, so no adjustments are required on the refrig and oil charge.
    Found refrig leak on liq line refrig filter element connection. Removed all refrig, found 65kgs short, total should be 285lbs (130kgs). Replaced oil filter and the refrig filter element (Part No: FLR 03018) Original filter I removed was P/No: FLR 0860. According to Trane spare parts (Dalkia) here in Melbourne the 03018 is the replacement for the 0860. Would anyone know if this is correct? It took them three attempts to finally send me the correct one (I hope).

    FLR03018 is correct part number to replace FLR0860, the serial # you supplied is incorrect and may explain your parts supply issues.

    Once correct amount of refrigerant was weighed in, started chiller. Have had constant faults of low refrigerant temp. Some days it can run for a few hrs, before failing. Have removed and checked all sensors, voltage and resistances, all o.k. Discharge superheat will read extremely low, so EXV closes down, even to 0% sometimes. Have even tried removing 5kgs, tested, then other 5kg of refrigerant. Did run alot better for a while, with disch superheat maintaining control set point and Exv sitting around the 15-20% open. After a few days, started failing again on low refrig temp. See details:
    Evap press:412kpa, disch:1256 kpa, Sat evap refrig temp:0.7 degrees C, sat cond temp: 34.9 , comp discharge temp: 52.7 , disch s/heat: 16.9 , disch s/heat control set point: 22.6 , EXV open %: 9.3 , steps open: 156 , evap approach: 5.7 , cond approach: 1.2 , evap ch water ent: 10 degrees C , evap ch w leave: 6.6 , cond water ent: 27.1 , cond water leave: 33.2.

    Without flow measurements am only guessing but there is something is way screwed up with your heat exchangers, As Jay points out you have 3.4 K delta on your evap but 6.1 K delta on your cond and your your superheat/evap approach is indicating poor evap heat transfer

    As a wild and probably incorrect guess from left field, assuming oil and refrigerant charges are correct, is your EXV operating in the correct direction, if two wires are swapped over it will run in reverse and could explain some of the symptons you are seeing. Post a full log with flow and RLA as it may help diagnose the problem.

    The condenser water uses only a throttling valve, no by-pass at c.tower, which is controlled by a separate siemens controller that someone has fitted in the past. This controller reads the system discharge pressure which drives the throttling valve.
    Would it be better for the chiller to operate this throttling valve? Would this set up be causing problems trying to maintain the discharge superheat setting? Maybe the chiller thinks it is still driving the throttling valve, but making no effect in raising the condenser water / discharge superheat temp, therefore using the EXV instead?

    RTHB UCP2 does not have EXV based differential pressure control. Have attached the recomendations for RTHB CW control. Throttling valve is acceptable, however direct from discharge pressure is not ideal with Delta T or Delta P preffered.

    Would anyone have any other ideas about this headache I have? Would be greatly appreciated. Cheers.
    The CW throttling valve should not be having any bearing on your chiller operation at the load/temps you posted it should be wide open.

    If this site is still Bayer they may have something for your headache
    Attached Files Attached Files
    Necessity is the mother of invention

  5. #5
    Join Date
    Aug 2009
    Location
    Prattville, Alabama
    Posts
    1,992
    Like Screwit, I'm curious about chill water flow rate, and also the application here. Is the chill water system an open or closed loop? Process or comfort cooling? Has chill water flow needed to be adjusted recently? And verify condenser water flow also.

  6. #6
    Join Date
    Dec 2008
    Location
    Dixiana, AL
    Posts
    2,609
    As has been stated, it seems that you have heat transfer issues in the evaporator. Since you have a weighed in refrigerant charge, I think I might take a look at fouled evaporator tubes or a bypassing divider plate in the evaporator water box based on the info that you gave. Obstructed tubes (not fouled) will do some really strange things to the evap operation, also. One of these things coupled with something screwy going on at times with the load or the condenser water could be pushing you over the edge.

  7. #7
    Join Date
    Oct 2003
    Location
    tidewater, va
    Posts
    2,135
    could your refrigerant be oil saturated?

  8. #8
    Join Date
    Dec 2005
    Location
    Melbourne, Australia
    Posts
    98
    Hi Guys,
    Found out recently that this chiller is still having issues with low refrig temp. I'm certain I read a reply from someone recently asking the question, If the exv is wired correctly, because it can run in reverse. When I first checked out this job I did notice that the number of steps didn't match up to % open. But didn't think any more of it, considering the chiller was installed in 1997. In the details listed on this thread, the EXV steps open is 156, while the open % is 9.3%. The Discharge s/heat control point is: 22.6, the actual disch s/heat is 16.9, so the EXV is commanded to close. Would I be correct in saying that at 156 steps the open % should be close to 100%? At 9.3% open the EXV should be approx 1500-1600 steps! (EXV has 1670 steps total). Does anyone agree that this EXV has possibly been incorrectly wired since day one of installation?

  9. #9
    Join Date
    Sep 2008
    Location
    A land down under
    Posts
    306
    Quote Originally Posted by chill bill View Post
    Hi Guys,
    Found out recently that this chiller is still having issues with low refrig temp. I'm certain I read a reply from someone recently asking the question, If the exv is wired correctly, because it can run in reverse. When I first checked out this job I did notice that the number of steps didn't match up to % open. But didn't think any more of it, considering the chiller was installed in 1997. In the details listed on this thread, the EXV steps open is 156, while the open % is 9.3%. The Discharge s/heat control point is: 22.6, the actual disch s/heat is 16.9, so the EXV is commanded to close. Would I be correct in saying that at 156 steps the open % should be close to 100%? At 9.3% open the EXV should be approx 1500-1600 steps! (EXV has 1670 steps total). Does anyone agree that this EXV has possibly been incorrectly wired since day one of installation?
    Easiest way to check, go to manual EXV control and slowly adjust open/close while observing your discharge superheat. If two wires are swapped over the EXV will run in reverse - some RTHB chiller did ship from Pueblo with incorectly wired EXV's but the problem was fairly obvious during commissioning
    Necessity is the mother of invention

  10. #10
    Join Date
    Jun 2010
    Location
    Tampa, FL
    Posts
    101
    I have had better luck by raising the tower water temp and allowing the cw throttling valve to maintain a more open position.Throttling valve is least desirable of cw control options.Too low a cw water flow seems to cause problems. Oil logged evap can happen quickly if dsh is allowed to run low for too long. Are all factory set points where they should be? Compressor load should be steady without a lot of hunting. Compressor should load slowly. Check chw control response setting. EXV seems ok from what you describe. Look for about 70% open at full load.

  11. #11
    Join Date
    Nov 2007
    Location
    Mississippi
    Posts
    1,303
    Had a RTHA225 act very close to the same as you describe. I ended up brushing tubes in evap and have not had a problem since.

  12. #12
    Join Date
    Mar 2009
    Location
    Queensland, Aust
    Posts
    12
    Hey Chill Bill

    I did alot of work on the RTHB when I was at Trane, there was alot of issues around nameplate charge being incorrect. Trane US issued service bulletin about correcting the charge levels when running.

    basic was to set the EXV at 60% in manual, at or near as possible to full load & preferably stable condenser water temp near 29'C. Then trim refrigerant charge in 5 kg lots, adding or removing to get the discharge superheat to within 1K of the discharge superheat control point.

    If over charged (yes you think 5kg should not be that much of problem) the discharge superheat goes very low and the EXV shutdowns to 'starve' compressor and lift superheat. Side effect was 'low evap temp' faults.


    Also 0 step = close. 1670 = open

    Hope this helps

  13. #13
    Join Date
    Feb 2010
    Posts
    81
    Quote Originally Posted by Aust chiltech View Post
    Hey Chill Bill

    I did alot of work on the RTHB when I was at Trane, there was alot of issues around nameplate charge being incorrect. Trane US issued service bulletin about correcting the charge levels when running.

    basic was to set the EXV at 60% in manual, at or near as possible to full load & preferably stable condenser water temp near 29'C. Then trim refrigerant charge in 5 kg lots, adding or removing to get the discharge superheat to within 1K of the discharge superheat control point.

    If over charged (yes you think 5kg should not be that much of problem) the discharge superheat goes very low and the EXV shutdowns to 'starve' compressor and lift superheat. Side effect was 'low evap temp' faults.


    Also 0 step = close. 1670 = open

    Hope this helps
    I agree 255 rthb exv could be on the cusp of a bigger capacity machine, limit the exv steps, bank up in condenser give it some liquid to boil off and raise low side pressure, were you seeing low discharge superheat faults, if so I would start looking there, however have heard of revisions to software also if any modules/ parts have been replaced problem could be there also, temp prob on discharpe pipe will dictate.

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