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Thread: Opinion

  1. #1
    Join Date
    Oct 2002
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    Hamden Ohio
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    Question Opinion

    When you have a walk in cooler with two evaporators and two condensors do you think its better to have one or two cold controls?

  2. #2
    Join Date
    Mar 2005
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    burlington county n.j.
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    i set them up with 2 controls with 1 set for a little bit higher temperature, sort of like a 2 stage system.

  3. #3
    Join Date
    Apr 2010
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    So Cal
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    Quote Originally Posted by t527ed View Post
    i set them up with 2 controls with 1 set for a little bit higher temperature, sort of like a 2 stage system.
    x2. Also, I like to flip the thermostat setpoints occasionally so that the lag compressor becomes the lead and vice/versa. That way the runtimes are equalized a little more.

  4. #4
    Join Date
    Oct 2009
    Location
    Raleigh, NC
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    776
    I almost always set them up with one control.

  5. #5
    Join Date
    Jun 2012
    Location
    Tenn
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    "Better" is a bit ambigous. Two controls reduces operating cost. Like someone else mentioned, it is best to be able to switch which is lead and lag, as it allows each compressor to wear evenly.

  6. #6
    Join Date
    Sep 2004
    Location
    Phoenix, Arizona
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    86
    Stage them with 2 tstats and change lead lag after a couple months.

  7. #7
    Join Date
    Jun 2007
    Location
    Williamsport, PA
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    164
    Quote Originally Posted by steve36558 View Post
    Stage them with 2 tstats and change lead lag after a couple months.
    I did one years ago with 3 thermostats and one seven day time clock. Every 12 hrs it switched from one unit to the other. both system tstats were set the same co 35 ci 40. Third tstat was an override tstat that brought on both sytems if temp rose to 45 and cut out at 38 for high load periods like loading with warm product or if one system failed. Has worked like a dream for years that way.

  8. #8
    Join Date
    Jun 2009
    Location
    DFW, TX
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    571
    Quote Originally Posted by johndief View Post
    I did one years ago with 3 thermostats and one seven day time clock. Every 12 hrs it switched from one unit to the other. both system tstats were set the same co 35 ci 40. Third tstat was an override tstat that brought on both sytems if temp rose to 45 and cut out at 38 for high load periods like loading with warm product or if one system failed. Has worked like a dream for years that way.
    That is a beautiful idea, but only if each evaporator is sized big enough to keep the entire box at temp. If the box requires 2 tons and each evaporator is 1 ton, then you will just end up freezing whichever evaporator is set colder (if you do the "lead-lag" as suggested by several). Most of the walk-ins I've seen with 2 evaporators actually need both evaporators to keep the box at temp. If the extra system is for backup, and each system is capable of keeping box at temp, then I think the 12/hr idea suggested here by johndief is the best way to go.

  9. #9
    Join Date
    Oct 2002
    Location
    Hamden Ohio
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    That was the problem I run into cooler one unit did all the work and keep freezing up even with long defrost times, the other unit would come on during defrost and keep it too cold to thaw. It was also in a slaughter house and the moisture in there is real high. Changed it to one control seems to be working beter.

  10. #10
    Join Date
    Apr 2010
    Location
    So Cal
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    69
    Quote Originally Posted by coyote View Post
    That was the problem I run into cooler one unit did all the work and keep freezing up even with long defrost times, the other unit would come on during defrost and keep it too cold to thaw. It was also in a slaughter house and the moisture in there is real high. Changed it to one control seems to be working beter.
    Having one unit come on while the other is in defrost should not have any effect on the other coil defrosting, unless you have air over defrost with a room temp below 36 degf. In that case you should be employing some other means of defrost (electric or hot gas). There is usually more than one way to arrive at the same goal. Having a thermostat for each unit allows you to do everything you could do with one thermostat but also have options to use other strategies as well.

  11. #11
    Join Date
    Feb 2009
    Posts
    130
    Try 1 thermostat and a time delay on solenoid of unit #2. Lead lag in my experience assures that both compressors wear out equally. I don't seethis as an advantage.

  12. #12
    Join Date
    Jun 2009
    Location
    DFW, TX
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    571
    Quote Originally Posted by coyote View Post
    That was the problem I run into cooler one unit did all the work and keep freezing up even with long defrost times, the other unit would come on during defrost and keep it too cold to thaw. It was also in a slaughter house and the moisture in there is real high. Changed it to one control seems to be working beter.
    So it sounds like in your situation, you need both coils to keep the box at temp. Just be sure you haven't overlooked that both systems are doing the same amount of work: in other words, confirm proper evaporator superheat on each coil. If one coil is starving, then the other coil will do all the work and freeze up.

    Certain box layouts may dictate the need for separate thermostats for each coil. For example, some convenience store walkin coolers are like a long hallway with glass doors for customers to get drinks. They are very narrow, and one side of the box can warm up while the other side stays cold, due to the airflow pattern of the evaporators blowing directly onto the glass doors. In that circumstance I usually see them having separate t-stats for each system and it seems to work well. I can also think of one particular restaurant kitchen walk in cooler - also a long narrow hallway type box, two evaporators, with a single thermostat. The back end of the box always gets too cold, while the end by the door always runs warmer.

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