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Hot gas reg

Discussion in 'Commercial' started by pintofstout, Oct 30, 2017.

  1. pintofstout

    pintofstout New Member

    Messages:
    1,541
    Location:
    Olean, NY
    Have AGS process chiller that i got dragged out to help diagnose, out on the annoying side of buffalo.

    40 HP semi hermetic recip with hot gas false load. No unloader, just hot gas for capacity control.

    Way before we took over the account, maybe ten years ago, a replacement evap bundle was installed. It's apparently undersized.

    Controller runs hot gas for entire cycle. It never powers down even when LWT is too high. This particular chiller, despite being a recip, controls based on LWT like a centrifugal or a screw would.

    So- hot gas has to be just right. It's not working just right though, LWT wanders. For five minutes it can't get below 60 and then 5 minutes later it's satisfying at 44 (55 target). Disconnect the solenoid and it's satisfied within ten seconds.

    The guy I'm helping, he's happy (initially it was running 30 second cycles, i fixed that with more hot gas).

    I'm not, which leads us finally to my question.

    The hot gas valve is heaving. Sounds like Darth Vader having an asthma attack. All over the neighborhood. I say it's bad and the heaving is a sign, i say replace it and you will have steady LWT.

    He says that heaving is normal and you could never expect a hot gas to provide stable leaving water. He says it's just cutting in and out (i don't even think in terms of cut in/cut out on a regulator).

    So- honestly i think the heaving alone is enough to condemn the valve. A properly sized regulator shouldn't do that. Should be a nice stable feed.

    The reason I'm asking is that this dude is the field supervisor, our discussion did get pretty contentious, and i want to know I'm right or wrong before i push anymore.




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  2. flange

    flange Act like you care and do SOMETHING!!

    Messages:
    12,870
    Location:
    IMT--in my truck
    hot gas regulator would not generally make much noise. dial in your desired pressure and away you go. by your description I would find out first what is controlling the solenoid and make sure its working right. many industrial type setups just energize the solenoid on a call for cooling, then let the reg open and close to maintain evap pressure. if its hunting that much its either fecked or possibly your expansion valve is doing weird shit.
     
  3. pintofstout

    pintofstout New Member

    Messages:
    1,541
    Location:
    Olean, NY
    Yeah the solenoid just comes on and stays on. Seems like a bad way to control but i guess they had their design in mind for a reason.

    But I've heard them heaving like that dozens of times and always assumed there bad because of it.

    There is no real call for cooling, aside from the cycling of the compressor based on LWT. Now that I've got it semi working it runs 100% of the time and never cycles off. It's run two two weeks without cycling of since my last visit and most of the process has been undergoing an overhaul, completely unused.

    It's not tied to the process because several different processes tie into the chilled water. I also think we should be controlling some sort of enable based on sump temp but that's another issue...


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  4. flange

    flange Act like you care and do SOMETHING!!

    Messages:
    12,870
    Location:
    IMT--in my truck
    it generally works pretty well that way, so long as you have a reg downstream and dial it in. I guess the hunting is possible if you have zero load I just never saw one do that.
     
  5. pintofstout

    pintofstout New Member

    Messages:
    1,541
    Location:
    Olean, NY
    Ok thanks man.


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  6. Ballvalve79

    Ballvalve79 It's only fire what could go wrong

    Messages:
    238
    Location:
    Northwest PA
    Initial post said process chiller could it be the load is all over the place. This could make suction pressure go nuts in turn the hot gas would respond to the changes. However a valve making alot of noise wouldn't be a normal thing. As @flange said the expansion valve may be doing something stupid as well, go back to the basics, in/out water, pressures and superheat/subcool. Just my .02.
     
  7. pintofstout

    pintofstout New Member

    Messages:
    1,541
    Location:
    Olean, NY
    Thank you ballvalve. I've been through all that but it's defiantly a valid thought.

    Load is stable, as it is non existent...

    Just runs all the time and when a load needs it, it's there.


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  8. Ballvalve79

    Ballvalve79 It's only fire what could go wrong

    Messages:
    238
    Location:
    Northwest PA
    Why couldn't a man put an unloader head or two on the compressor or better yet a smaller compressor. Just another random thought.
     
  9. HMD

    HMD does it matter?

    Messages:
    93,375
    Location:
    here
    so, is the head pressure hi enough, to give enough hot gas thru the valve, and to the bundle?
    i set one up a coupla weeks ago, operates totally different based on the head
     
  10. crackertech

    crackertech assholiness *

    Messages:
    91,455
    Location:
    Fl/IN/Ga/Ms/TX/NJ/VA/NC/TN

    That’s a good point Bob.
     
  11. HMD

    HMD does it matter?

    Messages:
    93,375
    Location:
    here
    that experiment worked, btw. as long as cdw stays above 85.
    multiple issues
     
    mike1020 and crackertech like this.
  12. crackertech

    crackertech assholiness *

    Messages:
    91,455
    Location:
    Fl/IN/Ga/Ms/TX/NJ/VA/NC/TN

    :thumb:
     
  13. LemonWizard

    LemonWizard Blinky Lights Wizard

    Messages:
    2,145
    Location:
    Ohighyo
    Does it not cycle because the reg is preventing it from going below setpoint? Is it supposed to cycle?

    Not familiar with process stuff.
     
  14. crackertech

    crackertech assholiness *

    Messages:
    91,455
    Location:
    Fl/IN/Ga/Ms/TX/NJ/VA/NC/TN

    As we new it would