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  1. #1
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    Multi Evap Single Condensor Issues

    I'm a long time follower of the site, not much for posts however. Looking for some insight into a recent condensor changeout. Old unit was a helical water cooled with R22,replacement is an air-cooled copeland(FFAP-020Z-CFV-072) running R438a. Single condensing unit feeds a Blanchard-Ness walk-in cooler (LSI-004-?) approx. 8'x8'x8', as well as two small prep tables. One is a 6 drawer unit, the other more like a sandwich prep station. Three t-stats, solenoids and three TXV's, one for each evap, and roughly 60' of piping, 3/8" and 3/4". New Copeland has digital pressure control with cutout at 25psi and cut-in at 65psi, box temps are all set at 38f. I'm struggling with determining an accurate charge and the correct setting for the pressure control, and should this be charged with all solenoids open? Copeland reference indicates liquid receiver capacity of 17lbs@90%, this likely includes condensor as well?
    The unit is charged with 18lbs and seems to run with suction pressure around 34psi and head pressure around 215psi, it regularly cycles on the LPC though. This system is beyond my usual scope of work, mostly A/C and more straightforward walk-ins. I'm lost on this one, any assistance is greatly appreciated.

  2. #2
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    IF that were my job I would want an EPR valve installed at the compressor.

    Without it the risk of a single prep table, requiring say; 1500 BTU's of capacity, is connected a 20,000 BTU condensing unit (I am just guessing at capacity - I didn't look up the compressor) is pretty large. A capacity mis-match that great is not good for the compressor.

    An EPR valve will reduce the compressor's pumping capacity to match the connected loading.

    The system has to be charged with all the boxes calling for cooling - LLS valves open. I would set the LP safety at the minimum that the manufacturer will approve - as close to 2 psi as possible. <g>

    Before calling it OK - I would want to watch it pump down all three cases at once - while watching the head pressure for any rise. A rise in head pressure during pump down indicates excessive refrigerant charge volume.

    PHM
    ----------------




    Quote Originally Posted by Hvacnorth View Post
    I'm a long time follower of the site, not much for posts however. Looking for some insight into a recent condensor changeout.

    Old unit was a helical water cooled with R22, replacement is an air-cooled copeland(FFAP-020Z-CFV-072) running R438a.

    Single condensing unit feeds a Blanchard-Ness walk-in cooler (LSI-004-?) approx. 8'x8'x8', as well as two small prep tables. One is a 6 drawer unit, the other more like a sandwich prep station.

    Three t-stats, solenoids and three TXV's, one for each evap, and roughly 60' of piping, 3/8" and 3/4". New Copeland has digital pressure control with cutout at 25psi and cut-in at 65psi, box temps are all set at 38f.

    I'm struggling with determining an accurate charge and the correct setting for the pressure control, and should this be charged with all solenoids open?

    Copeland reference indicates liquid receiver capacity of 17lbs@90%, this likely includes condensor as well?
    The unit is charged with 18lbs and seems to run with suction pressure around 34psi and head pressure around 215psi, it regularly cycles on the LPC though.

    This system is beyond my usual scope of work, mostly A/C and more straightforward walk-ins. I'm lost on this one, any assistance is greatly appreciated.
    PHM
    --------
    The conventional view serves to protect us from the painful job of thinking.

  3. Likes CEAS-AC-TECH liked this post
  4. #3
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    I agree with PHM with 3 dissimilar evaporators what's going to prevent just one low load unit from calling? EPR balances the loads.

  5. #4
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    To run three independent loads with a single compressor is always difficult to control but I see an additional issue here in what appears to me to be a vastly oversized condensing unit.

    If you follow what PHM was saying about how using an EPR will hold the evaporator suction where you want it and at the same time allow the compressor to rebalance to a lower pressure and hence a lower capacity which matches the load, then you will also see how when the existing system when running with all systems calling balances at 34 psi, that is the balance point of this system.

    You can use this balance point of 34 psig to get a pretty good idea of what the real load is by finding where this condensing unit would see that condition, and for R438A (MO99) that would be approximately 8°F SST. The capacity of the FFAP-020Z at that condition is about 9000 Btuh or so.

    The 8' x 8' walk-in would normally require a 25°F evap temp if the coil is sized properly and the two prep tables should be satisfied with a 20°F evaporator temperature, so I'm saying this system should have a condensing unit selected to give you 9000 Btuh at +20°F SST. The FFAP-020Z at that suction temp with R134A would have a capacity of 9000 Btuh.

    After verifying these loads I'd still add the EPR, but with R134A this system would certainly run a lot better.

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  6. #5
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    Thread Starter
    Thank you for that. Would three separate EPR’s be required for each evap? I will inquire with Copeland to confirm the lowest allowable LPC setting.

  7. #6
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    No..
    I would put the EPR on the common suction line.
    Right at the condensing unit would be ideal.

    Or...you could leave the walk in out of the picture and just have the EPR on the prep stations if piping allows it.

    Sent from my SM-G975U using Tapatalk

  8. #7
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    If he puts it only on the common suction all 3 coils would operate at the same pressure/temperature.

  9. #8
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    Yes; but so long as all three evaps are active they will all operate at the same suction pressure - NO MATTER if there is an EPR or not. Because when they are all running the combined heat loading and the compressor capacity would be balanced by the operating suction pressure.

    As the combined system runs at 34 lb. suction pressure now - but cycles on the LP safety at times - when less than three evaps are active I presume - I would set the EPR to maintain about 30 lbs evaporator pressure and set the LP safety control at about 2 lbs.

    The EPR would then trim the compressor capacity to match the load as well as it can easily be done. And stop all the compressor short-cycling.

    Wouldn't it?

    PHM
    ------------


    Quote Originally Posted by VTP99 View Post
    If he puts it only on the common suction all 3 coils would operate at the same pressure/temperature.
    PHM
    --------
    The conventional view serves to protect us from the painful job of thinking.

  10. #9
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    How would this resolve the issue of the compressor cycling on the LP control?

    PHM
    --------


    Quote Originally Posted by UmmScott View Post
    . . . . you could leave the walk in out of the picture and just have the EPR on the prep stations if piping allows it.
    PHM
    --------
    The conventional view serves to protect us from the painful job of thinking.

  11. #10
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    Quote Originally Posted by Poodle Head Mikey View Post
    Yes; but so long as all three evaps are active they will all operate at the same suction pressure - NO MATTER if there is an EPR or not. Because when they are all running the combined heat loading and the compressor capacity would be balanced by the operating suction pressure.

    As the combined system runs at 34 lb. suction pressure now - but cycles on the LP safety at times - when less than three evaps are active I presume - I would set the EPR to maintain about 30 lbs evaporator pressure and set the LP safety control at about 2 lbs.

    The EPR would then trim the compressor capacity to match the load as well as it can easily be done. And stop all the compressor short-cycling.

    Wouldn't it?

    PHM
    ------------
    In my experience with putting an EPR on a custom r404a prep table, the unit was running around 38 psi 5f SST, causing frequent ice ups. So I put the EPR at cond unit, set to about 54 psi 18f SST.

    I observed that as the box pulled down and EPR began to modulate, the suction pressure at compressor dropped down nearly to 20psi, which is much lower than it was before.

    Based on that I'm picturing the OP's cond unit might short cycle even worse with an EPR, although the coolers would run much better. I like IceMeisters idea of running a different gas, although setting a pressure control for r134a would basically guarantee lots of short cycling... I think we need a HGBP and desuperheating TXV too!

    Sent from my SM-G892A using Tapatalk

  12. #11
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    Quote Originally Posted by trippintl0 View Post
    In my experience with putting an EPR on a custom r404a prep table, the unit was running around 38 psi 5f SST, causing frequent ice ups. So I put the EPR at cond unit, set to about 54 psi 18f SST.

    I observed that as the box pulled down and EPR began to modulate, the suction pressure at compressor dropped down nearly to 20psi, which is much lower than it was before.

    Based on that I'm picturing the OP's cond unit might short cycle even worse with an EPR, although the coolers would run much better. I like IceMeisters idea of running a different gas, although setting a pressure control for r134a would basically guarantee lots of short cycling... I think we need a HGBP and desuperheating TXV too!

    Sent from my SM-G892A using Tapatalk
    The hot gas bypass with desuperheating TXV would be a very solid solution and would eliminate the need for an EPR (or multiple EPRs). A couple of years back I believe UmmScott had such a system and got it working quite well.

    Here's all one needs to know about Sporlan's HGBP valves: https://www.parker.com/literature/Sp...=10122&elqat=2

  13. #12
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    Thread Starter
    Thanks for all the advice, perhaps the 134a changeout is worthwhile.
    I’ll be doing my homework on the sporlan valves as well. PHM mentioned setting the LPC at 2 psi, what would be a recommended cut-in pressure?

  14. #13
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    Quote Originally Posted by Hvacnorth View Post
    Thanks for all the advice, perhaps the 134a changeout is worthwhile.
    I’ll be doing my homework on the sporlan valves as well. PHM mentioned setting the LPC at 2 psi, what would be a recommended cut-in pressure?
    Before doing a R134A change you need to verify that the existing FFAP unit would in fact have the capacity. Then do a load calc on the walk-in. get the walk-in evaporator model number and then get the manufacturer and model numbers for the prep tables so we can get some solid Btuh requirements for those.

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