Page 1 of 2 12 LastLast
Results 1 to 13 of 18
  1. #1
    Join Date
    Aug 2006
    Location
    Vancouver , Canada
    Posts
    300

    30HXC 126 - low load problems

    Greetings again:

    I thanks the chaps that responded to my thread last week on changing oil filters on this beast - that seems to have alleviated some problems, but others have surfaced.

    I know that low load scenarios are the BANE of chiller operators - oil return problems, short cycling etc., but I will give it to you quickly - BTW , I have good water flow with 10 - 11 deg. F @ 100% load.

    The chiller in question cools the rather large MCC ( 24 / 7 ) in the Recovery boiler building at a Pulp and Paper company. I am the sole HVAC guy, with 30 years under my belt, but my exposure to the new generation of screw compressor with all the associated electronics is very limited - I used to work on D/B vertical screws - maybe that cursed me ??

    Anyway, I quickly have a couple of questions - BTW, I changed internal and external oil filters on both A and B compressors on this machine last week, and while running, oil pressures seem OK ( less than 10 psi on the PD reading etc. ) There are two oil sight glasses on each system - I suspect the level should be at least between them, as the brass oil level float is centered between them. A compressor has the bottom glass full, sometimes the top glass has something in it, B compressor always has both glasses full. Is there a preferred level?

    Compressor A will start to unload as you get near the setpoint ( 44 F, chilled water, no glycol ) and cycle @ 10% ( at which time the hot gas valve opens ), back up to 24%, then up to 37%, even when I have a leaving water temp of 45-46F, entering about 2-3 F higher.

    Compressor B, running by itself @ the same conditions, runs @ 46%, with a 4-5 degree inlet ( higher ) temp. - The 46% is total unit capacity, and that is what it seems amperage wise - so it is basically running flat out - I have not seen it get to a point where the hot gas valve opens.

    Is there a specific control setting strategy that will help me on low load scenarios? Without some guidance, I don't want to be screwing around too much.

    I am sceptical to go changing parameters as the Carrier guy set it up back in May; the unit ran trouble free in the fall when we had similar ambient temps. - all in the 40 - 50 F range. It even ran trouble free when we were at the 20 - 35 F ambient for a couple weeks in December.

    I will also add that the condenser is Mill water that is metered thru the condenser via a Carrier supplied butterfly valve that gets a 4 - 20 signal from the board - the condensing temp. is set @ 90 F and even though the entering mill water is 44F, it does a good job of maintaining head pressure/temperature.

    Sorry about rambling on - I want to try to resolve this on my own, but we will call in Carrier if need be; we are a ferry ride from Vancouver and it isn't a simple chore to get here.

    I wish I had had more time to play with this unit, but as the only guy looking after 250 pieces of HVAC equipment that is 20 plus years old, well, you get the picture.

    Thanks;

    Dave Beauchesne CM
    aka : Freonguy
    Superheat and subcooling tell it all !

  2. #2
    Join Date
    Jan 2008
    Location
    Dallas ,Texas
    Posts
    3,718
    You wouldn`t happen to have a set of logs with exv position and modes would you ?
    UA 100

    It takes three people to do anything around here. Two do the work, one explains to the crowd of people who showed up when they seen smoke and flames.

  3. #3
    Join Date
    Aug 2006
    Location
    Vancouver , Canada
    Posts
    300

    Carrier chiller

    Thegoodlistener:

    Thanks for the reply -

    No I don't - All I have is the hand held navigator - I should get a laptop and necessary software to run it - the navigator is a PITA to keep cycling through to be sure -

    What ideas do you have on the EXV positions?

    Freonguy
    Superheat and subcooling tell it all !

  4. #4
    Join Date
    Jan 2008
    Location
    Dallas ,Texas
    Posts
    3,718
    Quote Originally Posted by freonguy View Post
    Thegoodlistener:

    Thanks for the reply -

    No I don't - All I have is the hand held navigator - I should get a laptop and necessary software to run it - the navigator is a PITA to keep cycling through to be sure -

    What ideas do you have on the EXV positions?

    Freonguy
    Honestly the Navigator is a badazz device.Beats breaking the laptop out for something the Nav will do. Well I was just cuious what the system is doing on A that B isn`t doing.
    UA 100

    It takes three people to do anything around here. Two do the work, one explains to the crowd of people who showed up when they seen smoke and flames.

  5. #5
    Join Date
    Aug 2006
    Location
    Vancouver , Canada
    Posts
    300

    A vs B

    Quote Originally Posted by thegoodlistener View Post
    Honestly the Navigator is a badazz device.Beats breaking the laptop out for something the Nav will do. Well I was just cuious what the system is doing on A that B isn`t doing.
    I haven't compared A vs B - EXV wise anyway. The biggest difference that I have seen is the fact that B doesn't seem to unload @ conditions similar to A.

    My point for mentioning the computer, is, are you not able to trend pressures, EXV position etc.? That would go some way as to figuring out what this thing is doing. Maybe I am wrong!?

    I am off today ( Friday ) and they never phoned last night - I set the temperature in the MCC real low for the weekend - see if I can make the unit run continuously - thanks for the feedback so far.

    Freonguy
    Superheat and subcooling tell it all !

  6. #6
    Join Date
    Feb 2003
    Location
    Wichita Ks
    Posts
    1,481
    Is the ball valve for the hot gas wide open? If it is it wll need adjusted. Directions for that is in the manual. If not wide open it still may be too far open.

  7. #7
    Join Date
    Jan 2008
    Location
    Dallas ,Texas
    Posts
    3,718
    Quote Originally Posted by freonguy View Post
    I haven't compared A vs B - EXV wise anyway. The biggest difference that I have seen is the fact that B doesn't seem to unload @ conditions similar to A.

    My point for mentioning the computer, is, are you not able to trend pressures, EXV position etc.? That would go some way as to figuring out what this thing is doing. Maybe I am wrong!?
    Well I am sure there is software that you can buy but in my opinion not necessary .
    I am off today ( Friday ) and they never phoned last night - I set the temperature in the MCC real low for the weekend - see if I can make the unit run continuously - thanks for the feedback so far.
    You mentioned low load problems but you didn`t mention any alarms ? Is there really a problem ?
    Freonguy
    I usually use the navigator but I do have a program that allows me to trend lots of points but you have to leave your computer onsite . Most of the time though it is not needed.
    UA 100

    It takes three people to do anything around here. Two do the work, one explains to the crowd of people who showed up when they seen smoke and flames.

  8. #8
    Join Date
    Jan 2005
    Posts
    604
    Well, I'm not sure you have a problem.
    Could you, very briefly state what the problem is.
    Both circuits are not always a 50 - 50 split.

  9. #9
    Join Date
    Aug 2006
    Location
    Vancouver , Canada
    Posts
    300

    30 HXC

    Guys:

    Yes, I was getting alarms; I don't have the numbers written down here at home - basically the unit would run for several hours, I would check on it during the day - OK. I have a room temp. MOPS ( Mill Operating System ) monitoring system - notice the temp. in the room starting to come up -

    This is a basic system - no fancy DDC controls, just an old Fisher pneumatic controller that monitors a chilled water setpoint @ the MCC AHU - as you near setpoint ( set @ 68 F ) there is a bypass valve that dumps chilled water back to the CW return line. This all modulates as it should, as far as I can see. There is no setback, as it is a 24/7 scenario - it tripped at 15:00 hours one day, and midnight 2 days later - shut the whole unit down - both compressors locked out.

    I changed the oil filters last week ( with help from posts to another thread - THANKS ) I since added 2/3 of a gallon of 220 to system A , as I was getting alarm # 124 ( I believe ) which is the float alarm ( the brass one near the oil sight glasses ) - The B compressor has both the oil sight glasses full all the time, while the A system has the bottom glass full all the time, but only occasionally you see a level in the top glass.

    Like I said, I set the pneumatic controller to 14 C ( about 60 F ) for the weekend to try to keep the bypass valve from dumping back into the return line, thus keeping the machine running longer. Dumb logic maybe, but I had to try something. I haven't got a call yet - maybe it is working.

    Freonrick:

    The ball valve is wide open at this point - once the system gets down to 10% when compressor A is running, the HGV opens, and the unit will stabilize; as the CW temp. comes back up, it goes to 24%, the HGV closes etc. When compressor B is running ( by itself ) though, I had leaving CWT of 42 to 43 F ( return of 47 F ) and the system was still @ 46% - why was it too not unloading ?? Then the unit cycles off, water temp gets up to 50 F ( SP 44 F ) and the compressor restarts.

    Thanks for the help so far guys - the unit ran from May 2009 till late December as it was set up by the Carrier dude with nary a glitch, now it is driving me nuts.

    Will keep you posted, and excuse me for being an old fart that has not had much exposure with these new fangled chillers !!

    Freonguy
    Superheat and subcooling tell it all !

  10. #10
    Join Date
    Jan 2008
    Location
    Dallas ,Texas
    Posts
    3,718
    What would you guess the volume of the chilled water system is ? Sounds like a bad design on the condenser supply loop also. I`ve seen alot of problems in the colder weather .
    UA 100

    It takes three people to do anything around here. Two do the work, one explains to the crowd of people who showed up when they seen smoke and flames.

  11. #11
    Join Date
    Apr 2007
    Location
    uk
    Posts
    199
    Hi Guys

    Are these oil sight glasses factory fitted and if so how long have the factory been fitting them as standard.
    Is it possible someone could take a photograph of them in relation to the oil level switch and send it to me. My email address is in my profile.
    The reason i ask is the Carrier French factory which supplys Europe don't fit them, but sounds a good idea to me takes a lot of the guesswork out of troubleshooting the oil level switch.

    In relation to the EXV position it has to be under 60% with a clear sightglass at 100% load, they will normally run between 30% and 40% at 100% load close to chilled setpoint.
    Hope this helps.

    Many Thanks
    Gibbo

  12. #12
    Join Date
    Jan 2008
    Location
    Dallas ,Texas
    Posts
    3,718
    Quote Originally Posted by Gibbo View Post
    Hi Guys

    Are these oil sight glasses factory fitted and if so how long have the factory been fitting them as standard.
    Is it possible someone could take a photograph of them in relation to the oil level switch and send it to me. My email address is in my profile.
    The reason i ask is the Carrier French factory which supplys Europe don't fit them, but sounds a good idea to me takes a lot of the guesswork out of troubleshooting the oil level switch.

    In relation to the EXV position it has to be under 60% with a clear sightglass at 100% load, they will normally run between 30% and 40% at 100% load close to chilled setpoint.
    Hope this helps.

    Many Thanks
    Gibbo
    Here let`s try this.
    Attached Images Attached Images
    UA 100

    It takes three people to do anything around here. Two do the work, one explains to the crowd of people who showed up when they seen smoke and flames.

  13. #13
    Join Date
    Apr 2007
    Location
    uk
    Posts
    199
    Top Man Cowboy

    Any idea how long factory have been fitting them ?

    G.

Page 1 of 2 12 LastLast

Posting Permissions

  • You may not post new threads
  • You may not post replies
  • You may not post attachments
  • You may not edit your posts
  •  
Comfortech Show Promo Image

Related Forums

Plumbing Talks | Contractor Magazine
Forums | Electrical Construction & Maintenance (EC&M) Magazine
Comfortech365 Virtual Event