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  1. #1
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    You have to smile!



    I attended a site yesterday where 2 identical water cooled chillers (shell and Tube condensers with vsd drive comps).
    1 chiller was tripping on High Motor current / high VSD temps. Whilst the other was evaporator pressure limiting.
    I decided to look at the High temp issue first.
    And despite the sites assurance that the condenser water circuit strainers had been cleaned only a couple of weeks previous I felt I should check them.
    This is what I found-


    Attachment 13842 Attachment 13843
    When cleaned and re-fitted the chiller worked like a dream!
    The second chillers condenser water circuit was checked and to be the same.
    That too worked like a dream!
    But that was evap pressure limiting?
    Ok. the system discharge pressure dropped by about 1 bar from 6 to 5bar (R134a)
    I think I understand what was going on.
    But if anyone likes to comment it would be appreciated.
    Grizzly
    Ps Site have decided in the short term to increase their filter clean frequencies.
    They are seriously good engineers working in a beautiful rural location.
    Hence the debris Via a Baltimore Cooling Tower.



  2. #2
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    Brian_UK is online now Moderator I am starting to push the Mods: of RE Site Moderator : and general nice guy
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    Re: You have to smile!

    Good catch Grizzly.

    People tend to forget that if they have a blocked strainer then there must be a load of crud instead the pipework sitting on the bottom of the pipework.

    After the strainer is cleaned and the pumps restarted all that dirt gets lifted and pumped straight into the strainer.

    I've had systems that took three section drain downs and refills with a strainer block and clean before I could get it to stay running.

    If you get a chance to flush the pipework then I'd say take it.
    Brian - Newton Abbot, Devon, UK
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  3. #3
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    Re: You have to smile!

    Hi Grizz
    How is the circuit evaporator pressure limiting ? is it by a suction line valve, or by speed controlling the compressor ?. or do you mean Crankcase pressure limiting ?.
    The condition of the strainers in the condenser lines are always a problem. I was called to look at a pair of Halls Duplex chillers, as they constantly tripped on high head pressures during the start up period first thing in the morning. Once the chiller had ran and tripped a few times it had pulled most of the load out of the chilled water circuits and would run OK for the rest of the day, but during the morning the room temperatures were always too high making the production area run slow due to the high temperatures. So I arrived early to watch the system start up for the morning production run. Sure enough the head guage showed the system constantly tripping on high pressure as the machine went to 100% loaded (6 stages of unloading ) The Condenser water was drained and the condenser end covers removed. The tubes were found to be coated in cement. The tubes were rodded through to remove the cement , but no strainer in the line could be found. The system was re filled and the system re run , but only with a slight improvement. On checking the cooling tower the return water flow was very poor. So a more thorough look to find a further restriction was started. After clambering through building voids etc etc, only a check valve was found in the line hidden up in the ceiling area, almost impossible to get to. But after getting the cover off, inside wasn't a check valve plate but a strainer . The strainer had to be chiselled out of the body as cement had solidified in the strainer gauze and body, basically blocking the water flow. After a bit of investigation , you could see the builders had used the cooling tower sump to mix their cement and concrete and the residue was being washed and trapped in the strainer. After removing the blockage , all OK.
    One of the worst systems for blocked condenser water strainers is a building on the embankment in London.
    The system is shut down for the Winter months but come the Summer the flow and return valves are opened up' to the 3 foot diameter pipes which run into the Thames. For the first three weeks of operation the 5 Centrifs were shut down one by one to clean the filters to the condensers every few hours, to remove the Coke cans, condoms , sanitary towels, body parts ,clothes , all sorts of debris dumped into the Thames . As they say its a SH-t job but someone has to do it. You country boys have it easy ha ha

  4. #4
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    Re: You have to smile!

    Quote Originally Posted by Grizzly View Post
    I attended a site yesterday where 2 identical water cooled chillers (shell and Tube condensers with vsd drive comps).
    1 chiller was tripping on High Motor current / high VSD temps. Whilst the other was evaporator pressure limiting.
    I decided to look at the High temp issue first.
    And despite the sites assurance that the condenser water circuit strainers had been cleaned only a couple of weeks previous I felt I should check them.
    This is what I found-


    Attachment 13842 Attachment 13843
    When cleaned and re-fitted the chiller worked like a dream!
    The second chillers condenser water circuit was checked and to be the same.
    That too worked like a dream!
    But that was evap pressure limiting?
    Ok. the system discharge pressure dropped by about 1 bar from 6 to 5bar (R134a)
    I think I understand what was going on.
    But if anyone likes to comment it would be appreciated.
    Grizzly
    Ps Site have decided in the short term to increase their filter clean frequencies.
    They are seriously good engineers working in a beautiful rural location.
    Hence the debris Via a Baltimore Cooling Tower.
    Grizzly,
    Could it mean cannot load any further due to discharge pressure limiting it?
    Might be the terminology or because other children tripping g it overloaded the suction pressure limited one.
    Last edited by RANGER1; 13-08-2015 at 08:33 AM.

  5. #5
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    Re: You have to smile!

    Hi Guys!
    Brian, your point about accumulative crap building up elsewhere is totally on the Money!
    No-one including myself considered how bad the strainers could be given how little time had elapsed since they were last cleaned.
    "We" have all agreed that site will clean more often in the short term.
    Glenn, very interesting tales from afor!
    As I understand the control strategy which is suction pressure related visa vi Comp speed.
    What I believe happened and having also discussed this with senior colleagues.
    What we think may of happened is the poor condenser performance due to its cooling water being choked.
    resulted in an insufficient supply of subcooled liquid. Which in turn would result to much flash gas being present.
    leaving the Lp side low and it reached it's alarm / control set points before the obvious Hp ones?

    Just a thought hence my question!


    Which is exactly what Ranger is implying!
    I think?
    Grizzly

  6. #6
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    Re: You have to smile!

    [QUOTE=RANGER1;308225]Grizzly,
    Could it mean cannot load any further due to discharge pressure limiting it?

    or because other chiller that is tripping is overloading the other running unit causing suction pressure to be to high, so it is limited by controller.

    Sorry trying to to do it on iPhone.

  7. #7
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    Re: You have to smile!

    [QUOTE=RANGER1;308242]
    Quote Originally Posted by RANGER1 View Post
    Grizzly,
    Could it mean cannot load any further due to discharge pressure limiting it?

    or because other chiller that is tripping is overloading the other running unit causing suction pressure to be to high, so it is limited by controller.


    Sorry trying to to do it on iPhone.
    Time may tell my friend, I know the system in question was set/up - charged correctly as the week before.
    That particular chiller system had a leaking PRV changed and was charged by weight (By Me!) to it's design charge.
    But something slightly unusual was happening and clearing the (discharge) condenser cooling circuit cured it?
    Grizzly

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