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  1. #1
    Join Date
    Feb 2006
    Location
    Phoenix,AZ
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    2,874

    Adjusting SH on multi evaps?

    Got a call to a big walk-in beer cooler not holding temp (45°F). Looked at copeland semi-hermetic first. Head frosted and discharge line luke warm. (floodback)
    Each evap had its own LLSV and T-stat. So i shut off one evap and adjusted TXV for 8 degrees SH on running one and then i shut off that one and adjusted other for 8 degress SH. Is this how you guys would approach this sitiuation or would you adjust them while both of them were running?

  2. #2
    Join Date
    Aug 2002
    Location
    Southold.calm
    Posts
    5,558
    It’s difficult to check superheat on a 5,000btu evaporator with 10,000btu’s of compressor. I recommend adjusting while both are running with the box near operating range.

  3. #3
    Join Date
    Sep 2002
    Posts
    510
    I have run into a similiar situation before.

    The two evaporator coils being in the same box or area should be controlled by one thermostat controling both liquid line solenoid valves.

    It will work much better that way.

  4. #4
    Join Date
    Sep 2008
    Location
    arlington, tx
    Posts
    225
    you always want to adjust at full load

  5. #5
    Join Date
    Nov 2005
    Location
    Haymarket VA
    Posts
    642
    Quote Originally Posted by kbghdg View Post
    Got a call to a big walk-in beer cooler not holding temp (45°F). Looked at copeland semi-hermetic first. Head frosted and discharge line luke warm. (floodback)
    Each evap had its own LLSV and T-stat. So i shut off one evap and adjusted TXV for 8 degrees SH on running one and then i shut off that one and adjusted other for 8 degress SH. Is this how you guys would approach this sitiuation or would you adjust them while both of them were running?
    just 14 * rule of thumb evap SH on high load then come back when its running on design temp set Sh good to go

  6. #6
    Join Date
    Feb 2006
    Location
    Phoenix,AZ
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    2,874
    Quote Originally Posted by mechanicalgsxr View Post
    you always want to adjust at full load
    Meaning what?
    I would think with one evap shut off and more refrigerant available and horsepower flowing to the other your greatest chance of floodback would then occur. Am i wrong?

  7. #7
    Join Date
    Mar 2005
    Posts
    202
    Quote Originally Posted by kbghdg View Post
    Meaning what?
    I would think with one evap shut off and more refrigerant available and horsepower flowing to the other your greatest chance of floodback would then occur. Am i wrong?

    If you adjust the valves to the proper SH while at full load then they should throttle back and maintain that SH as the box temp drops and the load is reduced. As was mentioned in an earlier post, If both evaps are in the same box why not control both LLSV's with the same t-stat.

  8. #8
    Join Date
    Jun 2001
    Location
    Michigan
    Posts
    12,077
    if the condensing unit has no way to shed load, such as Hot Gas By Pass, or unloading, I would not run those evaporators individually rather run on one stat.

    A walk in such as this, there is no need to control each coil individually. It's all doing one load.

    And if the coils were doing two separate load spaces, then obviously individual control is needed, then we we have to modify condensing equipment to modulate capacity.

  9. #9
    Join Date
    Sep 2008
    Location
    arlington, tx
    Posts
    225
    Quote Originally Posted by jwc64 View Post
    If you adjust the valves to the proper SH while at full load then they should throttle back and maintain that SH as the box temp drops and the load is reduced. As was mentioned in an earlier post, If both evaps are in the same box why not control both LLSV's with the same t-stat.
    what he said lol

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