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  1. #1
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    walk in with a redundant system

    We have a pharma situation I am looking for help on . There 4 walk ins at 4.c. 3 pipe design, Redundant system with 2 systems per room , each system capable of handling the load. they are set to alternate lead /lag . If load increase second unit come on . there are no interconnecting wires between outdoor and indoor .
    The controller works well enough ,with timed change over , alarm system etc., but can not distinguish when there is a faulty unit . There was just a total failure , system A was running and failed , but system B had already failed some time earlier , so there was a Sunday emergency transfer of stock. I checked the controller once I had system A running , and it was calling for system B , even though the disconnect was off .
    Thinking of a current sensor ( RIB ,have a large range ) . when a system is calling it will energize either of the 2 solenoid valves liquid line or the hot gas ,I will have to run wiring from the controller to the units to prove a unit is running a current sensor will tell me that ,( or may be a discharge line temp sensor ?) but unsure of how to incorporate it in to a manageable circuit , any one done similar , wiring ideas , or product info , would be appreciated . Jim

  2. #2
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    Do you have a diagram of the controller?

  3. #3
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    Now I'm confused. A wiring schematic would help
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  4. #4
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    this is a Norlake control which I reckon is a Carel PLC . The controller has a multitude of unused inputs and outputs . We are only using a couple of temp probes . for room temp . Fans run continuous, lights are run thru controller .
    to control the temp the selected unit say A. supply to cooling solenoid, temp satisfies , if it drops as it does after satisfying , supply to system .A hot gas solenoid . If temp rises 1 degree from set point system B will energies . A and B will be reversed lead / lag .
    If it alarms or a rising trend is seen a service call is placed . Have to improve that to big a flaw . A nd as I see it theonly way is to deterime that the actual selected unit is RUNNING .

  5. #5
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    Alternating the lead and lag throws a wrench into the machine. Could you set it up as a 2 stage system without the lead lag? Theoretically stage 1 would run until it failed and you could set up an alarm once stage 2 is energized.
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  6. #6
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    Someone makes a current sensor that runs off a card, and can provide a relay closure output. Call Carel and see iif there is an on/off input that represents feedback for proof of operation, and will alarm when the feedback response is missing.
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  7. #7
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    Quote Originally Posted by 2sac View Post
    Alternating the lead and lag throws a wrench into the machine. Could you set it up as a 2 stage system without the lead lag? Theoretically stage 1 would run until it failed and you could set up an alarm once stage 2 is energized.
    This, and you could manually switch the lead system on your annual pm or service call...

  8. #8
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    The daily switching of units is part of modern Lab specs it would seem. In the past a back up unit may sit idle for months and be short of gas or a seized fan when suddenly required. We have systems by BALLY and every time a system satisfies the alternate system is selected for restart
    Will find a way to incorporate proof of operation of the selected system in to the control circuit.

  9. #9
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    Don't know if this is what you have, Good Luck:
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  10. #10
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    Where I see the issue, and maybe I'm wrong, is with the alarm. If I understand this correctly, the system currently alternates compressors based on some timing parameters. It also uses the lag compressor for stage 2. Your alarm circuit would need to be smart enough to determine the lead refrigeration circuit and then alarm when it isn't running on a call for cooling.
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  11. #11
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    I believe and check with Carel first but it can be set up for Lead / Lag. First on First off. Then the alarm points can be entered.

  12. #12
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    Not sure how to implement, but a logic that says this system is calling. Then looks at the room temp to see if it is changing to the negative. If so, it is quiescent. If temp stays the same or increases for a specified time, it calls you. Then it says to its brother, you take the load and shuts itself off.

  13. #13
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    NORLAKE state the controller will have to be reprogramed . Sent an email to there engineers advising of our requirements . said we will fit a current sensor , and wire to the panel, with a closed signal as proof of operation when the selected compressor should be running , See what happens .
    this is a Carel Pro Logic Controller with a software program . Many unused inputs and outputs available . But it is set up real Dum and blind to what is happening with the room . Hi temp 8 c . send out alert swap units , but oh dear other unit is and has been faulty for some time ,. During routine operation controls temp at 4c , swaps to failed unit temp rises a degree bring back the other unit which it is programed to , thinks its a load issue , not a fault with the unit . May try and get in contact with CAREL but suspect may run in to politics there . Jim

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