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  1. #1
    Join Date
    Jul 2008
    Posts
    24

    Lieberts and High Head Pressure Limit Switch

    I have about 38-ton of Liebert cooling - all glycol condenser cooled.

    The building operates a 24x7x365 loop with roof top cooling towers.

    I am on the 1st floor, and for the past 2 years have been struggling with limited flow. We've compensated the limited flow by lowering the loop temp, so my glycol exit temp for most Lieberts is around 95-98 degrees (it used to be 105-110).

    Here is the problem, because flow is so poor, from time to time, little hiccups happen. The problem is those hiccups cause major issues for me. Last week for example, we think a small air pocket hit the 1st floor pump and caused momentary loss of flow. Well, that short loss of flow was a major issue for me and ALL my units went into high head pressure alarms.

    The problem is the Lieberts have to be manually reset when they hit high head pressure, someone physically has to push the reset button on the switch by the compressor. This is a data room, so if nobody is around its a major issue.

    I am brainstorming on ways to implement something that would allow me to remotely (over the wire) reset the high head pressure switch. Does any manufacture make a head pressure switch the automatically resets after 5 minutes, or automatically resets after the pressure return to normal ranges.

    The only idea I have so far is messing with the control wiring. The high head pressure switch is either normally open or normally closed (not sure which), when it goes off its just closing or opening that circuit. I could override that with a controllable relay circuit.

    Any ideas?

    Thanks
    John

  2. #2
    Join Date
    Mar 2010
    Location
    Kent, WA.
    Posts
    184
    even if you replace the manual reset pressure switch with an automatic one the liebert control has already seen the high limit and shut down on alarm. i guess you could go into the programming and adjust the alarm priority for the head pressure switch but at this point you are just messing with the design of the safety system built into the unit.
    at this point i would look into the flow issues and how to fix them rather than taking a chance on completely destroying a liebert.
    we have dealt with similar issues and have added a second water loop and towers to take some load off. seems these data guys racks get smaller yet more powerful creating more heat in tighter space. then they add racks with the new found space. it's a never ending battle.

    what temp are they trying to maintain in the data room. we did some experimenting with a data room that had been maintained at 71* and changed that to 80*. this was a traditional room without hot/cold isle containment. the racks could easily handle the temp rise and they saved tons on cooling costs.
    Experience
    Is what you get when you didn't get what you wanted.

    A positive attidude will not solve all your problems, but it will annoy enough people to make it worthwhile.

  3. #3
    Join Date
    Apr 2012
    Location
    Paper Street Soap Company
    Posts
    2,304
    Yep, auto hp reset is a bad idea.

    Is this your loop or are you tapped off a building loop ?

    I believe the HP is single pole double throw opening a control circuit and also closing a switch that sends a signal back to the micro.

  4. #4
    Join Date
    Jul 2012
    Location
    Southwest
    Posts
    114
    add an inline booster pump on the first floor? Those units have strainers, and are clean, correct?

  5. #5
    Join Date
    Apr 2007
    Location
    T.C minnesota
    Posts
    12
    Instead of wasting your time trying to put a bandaid on it you should solve the problem. Do you have any email or phone notification of room temp? If not it is easy and can be inexpensive to install. You can also install ICOM in all the units and then link it to sitelink, but its not cheap. There are alot of things you can do. Look into AFCOM, it is a organization for IT people that go over all aspects of a data center, you can get good info from them on local mechanical companies that will give you the options that best serve you. I could go over alot of things but not knowing what your room is setup like, I'm just pissing in the wind. Hopefully this helps

  6. #6
    Join Date
    Feb 2011
    Location
    Sacramento, CA
    Posts
    147
    Manual HPS are installed for a reason, If you trip it you need to look at it and see why it tripped. I dont know how many compressors I have replaced because it went into high head then auto reset untill it died. It will destroy the compressor ie. cook the oil, high pressure = high tempature. It has been mentioned here already and I agree with setting up some type of room tempature monitor that will send an alarm to a phone or email. We use ALC in my data rooms, in the critical areas we use sensors in the hot and cold rows so we can prevent problems. What would happen if you did not know that your condenser water pump died and your systems all had auto HPS's? Its cheaper to get some type of monitoring installed that to replace a half dozen 06D compressors. JMO
    I have done so much with so little for so long, that now I can do almost anything with nothing at all.

  7. #7
    Join Date
    Jun 2009
    Location
    StL, MO
    Posts
    580
    Fix the flow problem.

    Then, if the data floors really mean anything, address the single point of failure in your cooling system.
    UA LU 562

  8. #8
    Join Date
    Jul 2008
    Posts
    24
    All,

    The loop issue cannot be fixed. Its not even a long term issue, its a weird anomaly that occurs due to my location in the building. Landlord refuses to fix it.

    It only happens 1-2 times a year, we lose flow for about 20-30 seconds, then the flow returns. The loop is redundant, in 18 years we have never lost flow long-term. I am at the very bottom of the building, if the pumps hiccup or get hit with air bubble, the momentary loss of flow is worst for me and causes my units to trip. Once I reset, everything is back to normal.

    Problem is.... if I am not here to reset, the room will over heat.

  9. #9
    Join Date
    Dec 2001
    Location
    Phoenix, Az
    Posts
    1,235
    Quote Originally Posted by stinkypinky View Post
    Instead of wasting your time trying to put a bandaid on it you should solve the problem. Do you have any email or phone notification of room temp? If not it is easy and can be inexpensive to install. You can also install ICOM in all the units and then link it to sitelink, but its not cheap. There are alot of things you can do. Look into AFCOM, it is a organization for IT people that go over all aspects of a data center, you can get good info from them on local mechanical companies that will give you the options that best serve you. I could go over alot of things but not knowing what your room is setup like, I'm just pissing in the wind. Hopefully this helps
    Bingo. No excuse in this day and age for critical environments to not be monitored 24 hrs a day by computer or phone. Sitelink is the way to go. Hell, you can even have it call the service company so your IT guys don't get bothered at 2 AM.

  10. #10
    Join Date
    Feb 2011
    Location
    OH
    Posts
    149
    YOU HAVE RELIEF VALVES ON YOUR WATER OR GLYCALL CONDENSER THAT COULD RELEASE IF YOU DO THAT; I WOULD HOOK UP FLOW CONTROLE THAT IF I LOOSE FLOW MY BACK UP PUMP WOULD COME ON ,ALSO I WOULD TEST IT 4 TIMES A YEAR ..ALSO WOULD INSTALL 2 BALL VALVES TO ISOLATE IT FROM SYSTEM SO IF HAD TO BRING SYSTEM DOWN I COULD USE WATER BACK UP FROM THE BUILDING ; THIS WHAT IVE DONE ; R,S,E,S BETTER SEVICE THROUGH KNOWLEDGE;

  11. #11
    Join Date
    May 2000
    Location
    Salem, WI US
    Posts
    61
    You could install a differential pressure control to monitor your
    Loop Flow and program the Liebert Units to shut down in the event of loss flow and restart when the flow is re-estabilished.......
    Betabass



    Success is to be measured not so much by the position that one has reached in life as by the obstacles which he has overcome.

  12. #12
    Join Date
    Apr 2008
    Location
    Tucson, AZ
    Posts
    111
    What if you add a second, lower setting, high pressure switch with an automatic reset and time delay in series with the solenoid coil? This will pump down the compressor and shut it down before it trips the head safety. Put a 30 minute or so time delay on it so you don't get short cycle alarms.

  13. #13
    Join Date
    Apr 2013
    Location
    Long Island new york
    Posts
    20
    We installed sensaphone systems tied right into contacts on liebert units and programmed our phone numbers in, cheap and easy notification of hi temp, excess noise, etc.

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