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Thread: subcooling

  1. #1
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    Apr 2005
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    Hello everyone, Just new to the site and have alot of questions. (A) What is the effect of subcooling in relation to part load and full load, low ambient operation with a heli-rotor style or unloading piston compressor. What is the relation to part load, normal ambient operation at part and full load. I would think the load on the evaporator and position of the metering device would have some input on subcooling. Does subcooling rise or drop toward saturation in the condenser. (B) What does the effect of a liquid receiver have to subcooling down stream of the receiver, Would there be subcooling? Or since the reciever would have two phases the receiver/liquid line would be at saturation? Is that why alot of places use LPA pumps after the receiver to make sure subcooled liquid gets to the metering device.

    Thanks ej45

  2. #2
    Join Date
    May 2004
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    12,290
    Ej

    You ask your questions like an engineer friend of mine that has a master in physics. Slow down will ya?

  3. #3
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    I wanted to see alot of different ideas and inputs from everyone.

  4. #4
    subcooling is the amount of liquid stacked in the condenser.
    you cannot check subcooling or superheat or the charge when system is unloaded all checks have to be done fully loaded.
    as far as a reciever is concerned you check the subcooling before the reciever. recievers are usually used on refrigeration systems because refrigeration units do not use subcooler rows as air conditioning does.
    the point is subcooling tells you how much liquid refrigerant is in the condenser hence 0 subcooling = no liquid and is undercharged, 8 to 12 degrees subcooling tells us condenser is full and adequetly charged over this amount tells us system is overcharged, unless its a high eff. residential system which may by design need more subcooling.

    in a ball subcooling tells us how much refrigerant is in a system and superheat tells us whats wrong.

  5. #5
    Join Date
    Apr 2005
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    airworx, Thanks for your reply. I know what subcooling is and how to charge the system using subcooling. I am looking for system performance at changing loads and how subcooling relates to it. Using different metering devices with receivers and so on, not a text book answer.
    Receivers are used on large and small systems. For example liebert units that use mech. cooling in low ambient conditions and de-humidification units using reheat coils and normal condensers.

    [Edited by ej45 on 10-08-2005 at 12:23 AM]

  6. #6
    Join Date
    Nov 2004
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    Originally posted by ej45
    (B) What does the effect of a liquid receiver have to subcooling down stream of the receiver, Would there be subcooling? Or since the reciever would have two phases the receiver/liquid line would be at saturation? Is that why alot of places use LPA pumps after the receiver to make sure subcooled liquid gets to the metering device.

    Thanks ej45
    Since the reciever has both liquid and vapor,the liquid there will not subcool but the vapor there will condense.(This will make a new saturation temperture)

    I suppose there could be further subcooling in the liquid line if the conditions allowed.

    Liquid amplification pumps compensate for pressure drops in the liquid circuit.Liquid pressure (and saturation temperture) is raised to prevent flashing before the device.This will increase capacity without increasing compressor horsepower.



    Can you show some links or any info on the type of compressors you mentioned.

  7. #7
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    Apr 2005
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    I am just asking in general terms and wanted to start a general discussion about subcooling and how temps, loads, refrigeration valves and receivers effect subcooling.

  8. #8
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    Nov 2004
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    all righty...i will have to think about it though.
    low temp is not my thing really,but i will read about anything.

    some guy has 100+ posts tonight on "maybe the installers didnt purge with nitrogen",so i guess this should seem more interesting!
    Sometimes there are compounding complexities of multiple variables that are not intuitively obvious

  9. #9
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    Oct 2005
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    Fairfax, VA
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    "the point is subcooling tells you how much liquid refrigerant is in the condenser hence 0 subcooling = no liquid and is undercharged, 8 to 12 degrees subcooling tells us condenser is full"

    I had a semi hermetic condensing unit that had no subcooler and fed refrigerant directly from the condenser to a reciever, and unless the receiver was full (overcharged), there was no subcooling to speak of. This lead to wild swings in operation, where the liquid line was solid as long as head pressure was rising, but as soon as the pressures stabilized, the liquid (at zero* subcooling) would start to flash, leading to decreasing suction pressure, decreasing head pressure, and further starving the TXV as the warm liquid in the receiver really started to boil.
    Eventually the suction would bottom out about 5 psi, and gradually the unit would start to recover, with head pressure rising and feeding the evap properly, until the pressures would stabilize ...

    [Edited by Speedracer on 10-08-2005 at 03:48 PM]

  10. #10
    you measure subcooling out of the condenser not the reciever, and you were probably seeing the effects of a fan cycling switch where the head pressure rises and falls and in this instance you cannot correctly calculate subcooling.

  11. #11
    Airworx, I was just in your neck of the woods. Thursday I drive to Ft. Worth to do an install. Right off of 30 near the Christian university. (circle drive)

    write me, maybe we can join up next week when I return to do the start ups.

  12. #12
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    Oct 2004
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    Where is John Dalton when you need him?

  13. #13
    Join Date
    Oct 2005
    Location
    Phillipsburg PA
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    6

    Cool subcooling

    there you go again "BIG DADDY" asking high tech questions. by the way outside temp is not a good calculation for load it is
    your salution/air temp entering the evap from your setpoint i think??? email me @ nicoleb@pennswoods.net PS look at my reply for union questions. you will bust a nut. PPS i am out of there too and getting all kinds of training to be the best someday like you.

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