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  1. #1
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    Winter - Low Head Pressure



    Hi

    I finally end up making my condenser and running well in Ammonia System.

    I noticed that during cold weathers Discharge pressure reduce to 100 PSI.

    I want to know is it good to have lower Discharge pressure? If so how low it should be.
    Some technicians are in view that 100 PSI is not good enough for liquid to flow properly from condenser to receiver?

    Should I take measures to increase Discharge pressure by turning condenser fan off?



  2. #2
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    Re: Winter - Low Head Pressure

    skhan,
    The benefit of lower discharge pressures are less work for compressor to do as is not working as hard, so maybe lower compressor motor amps.
    As long as compressor can unload or control suction pressure in the desired area, not to low or evaporators may ice up in some cases.
    This is good, the only thing to watch is can the liquid from liquid receiver feed the evaporators OK & correctly so they still perform.
    Depending on your system TX valves need certain differential pressure to supply correct amount of ammonia to evaporator, or hand expansion valve open enough to maintain surge drum vessel.
    You would also notice if liquid was hung up in condenser, as liquid receiver level would be possibly to low.

    Can you tell us more detail of your plant & design like type of evaporators, expansion valves etc?

  3. #3
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    Re: Winter - Low Head Pressure

    skhan,
    Other things to consider is if plant had any hot gas defrost, if not no problem, if yes discharge pressure may have to be increased.
    If condenser fan was using more power than compressor at lower discharge pressure

  4. #4
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    Sep 2009
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    Re: Winter - Low Head Pressure

    In NH3 system

    we have pipe between condenser and receiver ( inlet of condenser and on top of receiver )we named it equalizing pipe
    in winter it should be open .

    so liquid stay in condenser and reduce our condenser capacity .

  5. #5
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    Re: Winter - Low Head Pressure

    Quote Originally Posted by mbc View Post
    In NH3 system

    we have pipe between condenser and receiver ( inlet of condenser and on top of receiver )we named it equalizing pipe
    in winter it should be open .

    so liquid stay in condenser and reduce our condenser capacity .
    Actually, equalizing line should always be open. It helps to free gravity draining and ammonia condensate will not stay in condenser.
    At lower condensing pressure plant run more efficient but oil carry over can happen.

  6. #6
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    Re: Winter - Low Head Pressure

    Dear Segei

    I am afraid to see No , when we open the equalizing pipe only gravity is forcing our NH3 to come from condenser to receiver .
    if it is closed , gravity + drop pressure ( from volume of liquid NH3 let to separator )

    in winter when we open that valve our level of NH3 liquid in receiver comes down and NH3 stay in condenser

    if you have system you can check it

  7. #7
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    Re: Winter - Low Head Pressure

    Quote Originally Posted by mbc View Post
    Dear Segei

    I am afraid to see No , when we open the equalizing pipe only gravity is forcing our NH3 to come from condenser to receiver .
    if it is closed , gravity + drop pressure ( from volume of liquid NH3 let to separator )

    in winter when we open that valve our level of NH3 liquid in receiver comes down and NH3 stay in condenser

    if you have system you can check it
    Hi, mbc.
    Properly designed and operated evaporative condensers don't need pressure drop to drain ammonia condensate from condenser to high pressure receiver. Typically, design issues of poor ammonia draining are undersized or no liquid traps. These tarps are very important for proper draining. Operating issue is presence air in ammonia system. This air prevent proper draining. Recently, I visited one plant and they had sever problem with ammonia draining. They kept 170 psig all year around to provide proper operation of the plant. A lot of energy was wasted. The reason of this poor performance was presence of air in ammonia system.

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