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  1. #1
    I was asked on an interview what I am comfortable with and not comfortable with.
    I listed chillers and heat pump defrost control boards.

    Of course I have worked on these systems, but was never trained on them nor servied them enough to get a good handle on them.

    So my question is; What do I need to know about chillers in general, to be most affective in servicing them?
    Let's narrow down the field here. Say 50 tons or less.

    What parameters need to be measured / tested, in order to troubleshoot the system?

    What are the operating parameters of a properly operating chiller?

    What are the common probelms?
    1) simple
    2) not simple

    What is the sequence of operation on a chiler system?


    Thanks

  2. #2
    Join Date
    Aug 2003
    Location
    Fort Worth, TX
    Posts
    11,376

    R-12

    I don't have much time around chillers myself, and would like to know more. I cleaned one while in the Navy (condenser water side, what we called "water lancing" to push out all the barnacles, etc.) and I've studied about them in books, perhaps the best I've read on them is in this book:



    Available at bookstores or Amazon.com. I learned about such terms as "approach", basic sequence of operation (similar to some of the "light off" procedures we did in my ship's engine room), COP, etc. I think this book covers the subject much better than the much exalted "Modern Refrigeration and Air Conditioning Book". I'll go on to say this book is written better than "Modern", and I thought for years "Modern" was the bee's knees.
    • 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.

  3. #3
    50 tons or less is more tha likely going to be a recip. Maybe tandem scrolls. I have never seen screws or centrifugals get that small.

    Trouble shooting recips is basically the same as troubleshooting comprable tonnage rooftops. Just substitute cold water for cold air.

  4. #4
    most chiller techs did not learn these systems going to school. a chiller technition is someone who has sat down and studied refrigant circuits and electrical circuits and just learned how air conditioning works. if you cant understand heat pumps then i wouldnt worry about chiller work.

  5. #5
    .....I never said I didnt know heat pumps.

    I just wrote that I was not comfortable with their defrost cycle printed circuit boards.
    I have not had a lot of troubleshooting experience with those boards! Period.

    I used to service G.E. Weathertron heat pumps.
    If you've been around a while, you may know the best personally.
    Anyone who can make one of them animals work ... can say they can make any heat pump work!

    Those were a real piece of .... "interesting-engineering". To say the least.
    I like heat pumps. They are the only thing that defrost itself.
    I hate defrosting indoor coils!!! And heat pumps solve that problem.



    I guess if people were that honest when they were interviewed, either employers would begin picking up the slack with employees education. Or less people would be accepted for jobs.


    Just read the posts here. Nobody has it all together.

    How about if you were asking that same type of question about ... say ... ice machines?
    And how would you feel if some guy responded back with your generic reply?
    If I got there first to post ... I woudl list out what the various seq of ops were for the most common three or four machines.
    Then I would list out what to look for on each.
    Then I would discuss operating parameters in general.
    Finally I would give you some links to find out more about them on your own.
    I would do that because I would want to help answer your questions.

    Now, do you have anything to contribute and help me?

    Thanks.



    [Edited by R12rules on 08-03-2004 at 01:39 AM]

  6. #6
    Join Date
    Dec 2002
    Posts
    9,871

    Chillers?? UMMMMM

    Takes a few years of hands on to be a compotent tech. Myself, I'm comfortable with all recips, screws, and scrolls. But when it comes down to a centrif, I don't even try to BS my way into working on one. Heat pumps are a piece of cake once you past the initial fear of all the control wiring.

  7. #7
    Join Date
    Dec 2002
    Posts
    9,871

    Basically R-12

    If you have not spent some years with great senior chiller tech, tell your prospective employer the truth upfront. Chillers are expensive and most times easily damaged in untrained hands.

  8. #8
    Join Date
    Jun 2004
    Location
    Richmond Virginia
    Posts
    1,078
    Small chillers are likely to be recips, then screws, and the largest are centrifugals. Let those that have spent years learning them handle the centrifugal teardowns. Learning how to take the proper measurements and observations to spot a problem with one would be the way to go. As far as recip chillers, there is not much different from a large package unit, instead of a blower fan you have a chilled water pump (and it has a flow switch to prove flow).

    As for defrost control boards and all solid state devices. To troubleshoot most, you will need some literature, a customer doesn't want to hear that you have to leave to go get some paperwork but that is what you will need for most. You're just checking inputs and proper outputs for those inputs and that's it. Don't get lost looking at all the little resistors and capacitors, you're not going to replace any of those!

  9. #9
    Join Date
    Aug 2003
    Location
    Ft Worth Tx ( North Richland Hills)
    Posts
    2,143
    Basic recip chiller info.

    1. Must prove chilled water flow before it can operate.
    many have a paddle type flow switch in the chilled water circuit, which seem to have lots of problems. A pressure differential switch is much more reliable. If it has a water cooled condenser, it might have a flow switch in that circuit too.

    2. Most chillers are designed for a 10 degree temperature drop (delta T). Entering water should be ten degrees higher than leaving water, which is usually set from 42 to 46 degrees.Having the correct water flow in gpms is very important. If you run the water through evap barrel too fast, not enough heat exchange takes place and your temp split will be too low.(leaving water temp will be too high)
    If you run it through too slow, you'll get a higher temp drop, which at first sounds good, but your evap refrigerant pressure will be too low and you risk freezing the water.

    3. Most air handler chilled water coils are designed for a 10 degrees rise in WATER temperature. Air temp drops can be as high as 30+ degrees.

    4. Any time a chiller shuts down the chilled water pump should continue to run for 5 minutes after the compressor shuts off in order to allow all remaining refrigerant in the evaporator to boil off. If shut down at the same time, the water could freeze and burst the copper tubing amd you're talking big bucks.

    How can you have any pudding if you don't eat your meat?

  10. #10
    Originally posted by seaboard
    Small chillers are likely to be recips, then screws, and the largest are centrifugals. Let those that have spent years learning them handle the centrifugal teardowns. Learning how to take the proper measurements and observations to spot a problem with one would be the way to go. As far as recip chillers, there is not much different from a large package unit, instead of a blower fan you have a chilled water pump (and it has a flow switch to prove flow).
    Now THIS is what I am talking about! Thank You!

    I have no intention of going out tomorrow and tearing down a chiller!
    It would be nice to participate in the project with someone who is experienced in that.

    What I am looking for is info simular to what you just gave me.
    If you think I'm THAT crazy, that I would tell someone I was an experienced chiller tech and was ready for anything... You've obviously spent waaay too much time at work lately!

  11. #11
    Originally posted by ozone drone
    Basic recip chiller info.

    1. Must prove chilled water flow before it can operate.

    2. Most chillers are designed for a 10 degree temperature drop (delta T).

    3. Most air handler chilled water coils are designed for a 10 degrees rise in WATER temperature. Air temp drops can be as high as 30+ degrees.

    4. Any time a chiller shuts down the chilled water pump should continue to run for 5 minutes after the compressor shuts off in order to allow all remaining refrigerant in the evaporator to boil off. If shut down at the same time, the water could freeze and burst the copper tubing amd you're talking big bucks.
    Ozone, this is most helpful.

    I've already serviced a chiller or two in my time. But I was not at my best because I never had exposure AND tips like these.

    A few simple tips like you provided and a rational person will go out and make some repairs in a much safer manner than one who is unaware of what they are looking for.
    I have been in this industry long enough to know where to draw the line and stop.
    If I encounter something I am not sure of, I can ask for a second opinion over the phone.

    Now when I locate literature on chillers, I will have some knowledge in order to make sence out of the info.

    Thank you very much.

  12. #12
    While i agree in part that it takes many years to actually get good on chiller's, The majority of chiller problems are due to water flow, tower fans, (for water cooled) and electrical. I'd have to say that at least 60% of the problems i encounter are flow switches, pumps, and tower fans. Nowdays with all the drives these units have, i have had to learn a good deal about them stupid things too.

    On the older chillers you will find many familiar controls that you are used to. On the newer ones you will have to bone up on your DC knowledge. There is also a lot of great info to be found on the different manufacturers websites concerning chillers and their operation.

    Learning to operate the different control packages of individual chillers is a must. Most of the newer chillers have interface panels that read out exactly what the chiller is doing at that moment in time. If for example the front panel indicates a leaving water temp of 48 degrees at 87% current, and the machine log shows a past history of the same readings , then we can assume the chiller is operating normally.

    One can actually get pretty close on these things just by being able to compare the current readings to the logged readings and then making a decision based on this data....Dont laugh, there are maintenance men doing this even as i type!

    Believe me R12 when i say that this stuff is not that hard... if it were i could not do it. I also agree with your being honest about short commings. This is something that all of us have, and too few will admit. I couldn't even dream of working on an ice machine.

  13. #13
    Join Date
    Apr 2004
    Location
    Winnipeg,MB,Canada
    Posts
    93
    Chillers- most important, good water flow, what is the pressure differential across those heat exchangers? Too high of a diff are tubes plugged, too low is strainer plugged? Either exchanger, get used to guage readings more info the better. Also, cut out settings are different, between air cooled and water cooled, with chillers hands on, being fed to the wolves is the best education, you will know when you're getting it right by the sound they make, good luck.

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