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  1. #1
    Join Date
    Jan 2013
    Location
    Wisconsin
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    23

    Rack Systems in Low Ambient Conditions

    Thought this would be an appropriate topic since a deep freeze is moving throught the upper midwest. What is everyones take on controlling head pressure to keep freon from logging in the condenser during low ambient conditions? Whats the best way to accomplish this? How does everyone go about setting the holdback valve (A8 or ORIT)? Any particular brand of system or setup that seems to handle colder conditions better? And GO!.. . . . . .

  2. #2
    Join Date
    Sep 2008
    Location
    Western PA
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    25,395
    Timely topic...

    Your FIRST line of defense against logging refrigerant in the condenser is properly setup condenser fan cycling controls. I've heard both pro's and con's of using them, but I'm in favor of cycling the fans off during low ambient conditions.

    The ORI/ORO (A8/A9 is what I typically see) setup is to manage and maintain proper liquid pressure in the event that one of those controls fail.

    Setting those valves is fairly straightforward. I like to go high on the ORI valve, then dial back to the pressure that I want and go low on an A9 and dial up to the pressure that I want. Just seems to make for a more accurate setting that way.

    WHERE you set those valves is a whole topic unto itself.

    A more specific question or questions is bound to get a more specific and accurate answer.

  3. #3
    Join Date
    Sep 2008
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    Western PA
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    Guess I forgot to include something important. Maybe the most important thing.

    Make sure the rack has enough gas in it.

    You are going to log SOME refrigerant in low ambients. This is just a part of life.

  4. #4
    Join Date
    Sep 2007
    Location
    Denver , Co.
    Posts
    109
    I think the best way is splitting the cond. some Walmart's use this along with fan cycling , im not a big fan of head masters .

    Ice V
    Outlaw guns? only outlaws will have guns
    Those who live by the sword are SHOT by us who don't.

  5. #5
    Join Date
    Sep 2008
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    Western PA
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    Quote Originally Posted by IceVicious View Post
    I think the best way is splitting the cond. some Walmart's use this along with fan cycling , im not a big fan of head masters .

    Ice V
    Condenser splitting is a secondary method, used along with fan cycling.

    It doesn't alleviate the need for low ambient valves.

  6. #6
    Join Date
    Feb 2008
    Location
    California
    Posts
    2,064
    you're gonna need to start stacking the coil with liquid at some point if it gets cold enough.

  7. #7
    Join Date
    Mar 2004
    Location
    Las Vegas, Nevada
    Posts
    1,647
    Interesting topic. We've had cold weather-related issues here in Vegas, believe it or not. Most of our troubles manifested in Floodback in Medium Temp equipment. The problems have been tracked to two main contributing factors:

    1) Most of the Medium Temp equipment are running on non-adjustableTXVs.

    2) Energy Management strategies have been tweaked and re-tweaked, mandating colder & colder Dropleg Temps.

    We found at various locations, Dropleg Setpoints had a parameter that would not allow Dropleg Temp to exceed 25 degf over Ambient. So we ended up with TXVs sized for 90 degf Condensing, running 50 degf Liquid.....

    Can't change Operating Parameters without going through Congress. Can't install Adjustable TXVs without going through Congress...

    Problem solved itself when the earth tilted the cold y'alls way.

    For now.
    The views and opinions posted here are my own. They do not reflect the corporate policies of my employer and will most likely get me fired at some point.

  8. #8
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    Sep 2008
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    Western PA
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  9. #9
    Join Date
    Sep 2011
    Location
    Plainfield IL
    Posts
    101
    No matter what your going to log Freon in the condenser. The hard part is settiong your A8 and A9 valve. Its best and easiest to set when outdoor ambient is about 40 Degrees F. I always set the A8 valve first. That's your holdback valve. Put your high side gauge on the A8 pressure port and turn the stem clockwise and watch the pressure rise past your desired setpoint. Be sure the manual stem is in the automatic position too. I like 180PSI for my set point for the A8 and 165 for the A9. If you want to log less gas go for a lower A8 setpoint but be carefull. If you go to low your TXV may not work properly. If your using balance port TXV's you should not have a problem.

    Once your pressure at your A8 valve climbs past your desired set point you know the A8 is functioning. Now slowly start turning adjustment stem CCW and bring your A8 to your desired set point and lock it down with the lock nut.

    Now put your guage on the A9 port. If your A9 if feeding the line should be hot. If its not hot its not feeding. Lets assume the line is cold. Turn the adjustment stem cw to open the A9 and bring your receiver pressure up to 165# and lock it down. Now your set.

    Next check your receiver level and add freon if nessessary. Try to maintain at least 5% receiver on the coldest day of the year. The warmer it is outside the more freon you should have in the receiver. Don't ever touch the valves again.

    I hope this helps you guys out. Be patient if your setting the valves on the coldest day of the year. It takes time to build up the pressure.

  10. #10
    Join Date
    Jan 2006
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    DFW Metroplex
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    Great responses!

    Ok.....now, how do you set an A8/A9 valve when the outside ambient dictates a higher SCT than your desired valve setting (summer)?
    "The problem is the average person isnt tuned in to lifelong learning, or going to seminars and so forth. If the information is not on television, and its not in the movies they watch, and its not in the few books that they buy, they dont get it" - Jack Canfield

  11. #11
    Join Date
    Sep 2008
    Location
    Western PA
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    Quote Originally Posted by markettech View Post
    Great responses!

    Ok.....now, how do you set an A8/A9 valve when the outside ambient dictates a higher SCT than your desired valve setting (summer)?

    The A9 valve can be set any time. Ambient isn't a factor in setting them. I've done in the middle of summer.

    The A8 on the other hand.....

    About the ONLY way I could see being able to set it would be to take the rack offline, isolate and pump out the piping with the A8 in it and use nitrogen to adjust it. I've never tried it, but Phase Loss has said that he's done it that way.

  12. #12
    Join Date
    Jan 2006
    Location
    DFW Metroplex
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    Quote Originally Posted by jpsmith1cm View Post
    The A9 valve can be set any time. Ambient isn't a factor in setting them. I've done in the middle of summer.

    The A8 on the other hand.....

    About the ONLY way I could see being able to set it would be to take the rack offline, isolate and pump out the piping with the A8 in it and use nitrogen to adjust it. I've never tried it, but Phase Loss has said that he's done it that way.
    Right - A9 is not a problem regardless of OAT/SCT

    Let me run this scenario past you with regards to the A8 and tell me what you think:

    • Gauge up at inlet to A8
    • Close off the drop leg isolation ball valve (typically installed upstream of the A8)
    • Close off A9 valve to receiver.
    • Back locknut off to end of adjustment screw and turn A8 adjustment screw CW to stop
    • Allow receiver to pump out to the the point where receiver pressure is at a value less than desired A8 pressure set point.
    • Shut down pumps
    • SLOWLY open drop leg isolation ball valve until gauge reading matches desired A8 set point.
    • SLOWLY turn A8 adjustment screw CCW until gauge pressure drops
    • Set locknut and return system to full operation
    "The problem is the average person isnt tuned in to lifelong learning, or going to seminars and so forth. If the information is not on television, and its not in the movies they watch, and its not in the few books that they buy, they dont get it" - Jack Canfield

  13. #13
    Join Date
    Sep 2008
    Location
    Western PA
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    It would probably get you close.


    You could also set it at the lowest point local ambient will permit, then reduce the setting per the X# per turn (I've seen it written somewhere) to approximate target desired.

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