Page 1 of 3 123 LastLast
Results 1 to 13 of 29
  1. #1

    Pressure on water cooled condensing units

    Hello to all,
    Looking for information on water cooled condensing units for medium temp walk in coolers. I have an account that has several constant loss water cooled condensors. As I have just started working on them, all I know of their history is that they have been horribly neglected. (Evap coils plugged so bad you could not see light through them, etc...) I've worked on various water cooled units in the past (water cooled heat pumps, Liebert units, Desert Aire, etc...) but have always been able to get manufacturers instructions regarding appropriate head and suction pressure based on incoming water temp and delta T across the coil. However, on these units, due to their age and lack of tech support from Copeland, I want to be certain that I am diagniosing these units correctly. Any help anyone might be able to offer regarding the following questions would be greatly appreciated.

    1) Water is flowing through the condensors even with the compressor off. Is it possible that previous techs tried to compensate for a fouled condenser by opening up the regulating valves? If it is possible to compensate with regulator settings, how would you diagnose a fouled condenser?

    2) Is there a rule of thumb regarding approximate head pressure based on inlet water temp and delta T across condenser? (As with the ambient +30 average on air cooled condensers)

    3) What would be appropriate sub-cooling and super-heat values for this style of unit?

    4) I would like opinions on the merits of using 414 (Hot Shot) versus 404 as a replacement refrigerant on these units. They are R-12 units, several of which are low on charge. I realize that the TXV should be changed but other than that are there any advantages or drawbacks to either refrigerent. (Compressors are Copeland semi-hermedics.) I have both refigerents in the truck and have used both in the past but would appreciate anyone elses opinions.

    I will be suggesting an upgrade to exterior air cooled condensing sections but need to keep these dinosaurs running for the interim. Also, any info regarding refrigeration engineering/technical resources would be great. You know, teach a man to fish... Thanks in advance for any help.

  2. #2
    Join Date
    Dec 2011
    Location
    Michigan
    Posts
    119
    Why not use R409 on top of the R12 dial them into 150psi set it and forget it.

    Sent from my HP touchpad running CM9 ICS

  3. #3
    Join Date
    Jun 2007
    Location
    Williamsport, PA
    Posts
    165
    1) Water is flowing through the condensors even with the compressor off. Is it possible that previous techs tried to compensate for a fouled condenser by opening up the regulating valves? If it is possible to compensate with regulator settings, how would you diagnose a fouled condenser?
    I have found that when the water does not stop flowing through the valve even when it is off it is the seat in the valve its self is bad if it is a penn
    johnson they have a repair kit.

    2) Is there a rule of thumb regarding approximate head pressure based on inlet water temp and delta T across condenser? (As with the ambient +30 average on air cooled condensers)
    Ambient will not affect the condensing pressure on water cooled units, that is why they are used.

    3) What would be appropriate sub-cooling and super-heat values for this style of unit?
    Superheat same as normal 10 deg for medium temp, superheat is controled by TXV.

    4) I would like opinions on the merits of using 414 (Hot Shot) versus 404 as a replacement refrigerant on these units. They are R-12 units, several of which are low on charge. I realize that the TXV should be changed but other than that are there any advantages or drawbacks to either refrigerent. (Compressors are Copeland semi-hermedics.) I have both refigerents in the truck and have used both in the past but would appreciate anyone elses opinions.
    Cant use 404A in r-12 compressor. Use whatever R-12 replacement you are comfortable with. Hot shot will work just fine.

    I will be suggesting an upgrade to exterior air cooled condensing sections but need to keep these dinosaurs running for the interim. Also, any info regarding refrigeration engineering/technical resources would be great. You know, teach a man to fish... Thanks in advance for any help.
    [/QUOTE]I would not be too quick to remove them and replace them with air cooled

  4. #4
    Join Date
    Feb 2010
    Location
    NE Alabama
    Posts
    301
    My biggest question is where is the water for these units coming from. If these systems aren't being fed from a well the savings in cost of water is a huge selling point for replacement once they have failed.

  5. #5
    Join Date
    Mar 2007
    Location
    NW AR
    Posts
    2,478
    It generally comes from city water supply

  6. #6
    Join Date
    Jul 2000
    Location
    Guayaquil EC
    Posts
    10,264
    The standard setting for a water regulating valve is at the pressure corresponding to 105ļF SCT (Saturated Condensing Temperature).

    For R414B (Hot Shot), that would be 149 psig.

    Set the valve and if it doesn't close when the compressor is off, rebuild it or replace it.

    R404A will not work as a replacement refrigerant for R12. It will overload the compressor, big-time.

  7. #7
    Join Date
    Jul 2000
    Location
    Guayaquil EC
    Posts
    10,264
    Quote Originally Posted by btack View Post
    Why not use R409 on top of the R12 dial them into 150psi set it and forget it.
    Mixing refrigerants?

  8. #8
    Join Date
    Dec 2011
    Location
    Michigan
    Posts
    119
    We have been using R409 as a drop in replacement for R12 for as long as I have been around (11 years) with out a problem. While the amount of equipment that contains R12 has diminished over time still have to pull out the 409 a few times a month

    Sent from my amazing 4G device

  9. #9
    Join Date
    Sep 2008
    Posts
    577
    I wouldn't touch that charge until I repaired or replaced the water pressure regulating valve. I've also been adding a water pressure switch (square d 9013FRG12J35) to all my water cooled systems.

    I always advocate for air cooled if at all possible. They waste an incredible amount of water.

  10. #10
    Join Date
    Nov 2008
    Location
    Altamont, IL
    Posts
    371
    I've tried rebuilding a couple of the J-P water regulating valves. The seat is very difficult to remove and the gunk built up in the valve is hard to remove. Considering the time involved in rebuilding and the rebuild kit cost I choose to replace The whole valve. You may have to recover the charge or use the ice machine warranty trick and pinch off the tubing to connect the line to the valve.
    In GOD We Trust

  11. #11
    Thanks to all who replied. It appears there is still ďdissention among the ranksĒ regarding refrigerant retrofits. I was told by a local vendor that heís heard of many techs who will top off a system with 414. One of the posts had recommended topping off with 409. Iím uncomfortable with this, as Iím not familiar enough with the various refrigerants to know which are compatible and which are not. I was always under the assumption that you never mixed refrigerants in the field so I always recover and retrofit with virgin refrigerant (although I know thatís basically what the blends are anyway). Regarding the question with refrigerant choices for R-12 medium temp retrofits Iíd like everyoneís opinion on the best (least trouble prone) refrigerant to use. Iíve used 414 in the past, but;
    1) Itís getting expensive
    2) Itís got 22 as a component
    3) Itís not recognized by Copeland as an acceptable refrigerant
    Considering these facts, what is the general consensus regarding the best long term retro fit refrigerant. (I must be doing something wrong in the search field, as I didnít pull up any matches. Iím sure this has been beaten to death already. Maybe Iím too specific with the search content. Any references are welcome) Copeland recommends 401A (which is what is in the unit Iím working on) in this application, but a local refrigeration contractor told me he would never use 401A again after experiencing problems with it on multiple jobs. Opinions?

    In my original post, I should have been more specific. I am aware that ambient in the room has no effect on head pressure with a water cooled condenser. My question relates to what the head pressure should be based on incoming water temp. In discussing this over the past few days, several local techs have said that the head pressure should be whatever the pressure for a refrigerant corresponds to at 105 degrees(consistent with what icemeister posted Thanks for the response). As to the regulating valve, it should be set to maintain that pressure (for 401A approx.156#). If the entering water is colder the valve will close somewhat to restrict the water flow. With warmer water the valve will open more, thereby maintaining a fairly consistent head pressure. Am I understanding this correctly?

    BTW, the condensers are using city water and dumping into the sewer, so the facility is getting hit both with the water charges as well as the increase in sewer use fees based on consumption. Thatís the reason Iím suggesting replacement with air cooled condensers as the units begin to fail.

    The reason for the post is that I feel I might be missing something. The compressor performance data is as follows. At a satisfied box (38 degrees) I get; 103# discharge, 1 degree subcooling,17# suction, 53 degree superheat. 12 degrees delta-T across the water side of the condenser, 58 degree entering water temp. 35 degree entering air temp, 28 degree discharge air temp. 4.74 amps. If I begin to close the regulating valve to restrict the water, the head pressure goes up but as it does, the amp draw goes above RLA (5 amps). I canít get anywhere close to 125, never mind 156. when I first started working on it the evap was completely plugged (couldnít see light through the coil) It took me three hours to get it clean. I thought someone prior to me may have come in and overcharged it without looking at the coil, but the low subcooling value and the high superheat makes me think itís undercharged. If thatís the case, then why the high amps? If the valve plate was leaking by, I would expect the amp draw to be low due to the decreased load. It does not have a pump down solenoid, but I will try to pump it down tomorrow to check the valves. Any suggestions would be greatly appreciated.

    As a side note, refrigeration service is comprising a greater share of my business than in the past. In an effort to educate myself more about this end of the industry, I would welcome any suggestions as to resources which the members feel would be valuable. (RSES, ASHRAE, etc) I am primarily interested in the deeper engineering aspects of refrigeration as it would relate to being a more well rounded technician. I have an S-1, P-2, L-6 and SM1 license, but would consider my refrigeration knowledge average and would like to be better equipped when I run into issues like this.

    I would like to extend a sincere thank you to all who are willing to share their experience to those of us (me especially) who value and appreciate it. Life experience is hard to come by. I hope one day that I can reciprocate and contribute to this community. Thanks again.

  12. #12

    Head pressure

    Just read a great article on the site about RLA refering to rated, not running amps. I will look up the compressor data now if it's still available for what I assume is a pretty archaic compressor.

    Six munce ago I cudnt evn spell cervix teknishun, and now I are wun!

  13. #13
    Join Date
    Jul 2000
    Location
    Guayaquil EC
    Posts
    10,264
    What's the compressor model? It would be quite helpful so we can all stay on the same page with this. I'm curious about that rapid amperage increase when trying to raise the head pressure.

    If this system current has R401A (MP39), there's no reason to change it for something else unless you have some driven desire to go to an HFC. I've used R401A since 1994 with no major issues.

    For an HFC you basically have two choices. One is R134A which requires an oil change to POE oil. The other is R438A (DuPont Isceon MO49 Plus) which will work well with your existing mineral oil.

    If the compressor is very old, you may want to check before opting for R134A and POE oil because seal materials from years ago may not be compatible with POE. There may be compatibility issues with the solvents used in its original manufacture as well.

Page 1 of 3 123 LastLast

Posting Permissions

  • You may not post new threads
  • You may not post replies
  • You may not post attachments
  • You may not edit your posts
  •  
Comfortech Show Promo Image

Related Forums

Plumbing Talks | Contractor Magazine
Forums | Electrical Construction & Maintenance (EC&M) Magazine
Comfortech365 Virtual Event