Results 1 to 3 of 3
  1. #1
    Join Date
    Aug 2014
    Location
    Canada
    Posts
    2
    Rep Power
    0

    low ambient condenser operation



    Hello,

    Hope I can get some help with this concept I am struggling with.

    What happens to the refrigeration cycle at extremely low ambient temperatures. If there is nothing to regulate the system, wouldn't the fluid exit the condenser at an extremely low temperature? And if that were to happen, the refrigeration cycle would not be possible.

    Is there always, without stating it, a system in place (such as an ORI/ORD) that regulates the fluid at the condensor exit (or, more pertinently, expansion valve inlet)? Can I correctly assume this to be the case if I know that the condensor is experiencing free cooling.

    Would the condenser type have an affect on this? Air-cooled vs evap condenser for example?

    In other words, if someone claims that there commercial refrigeration system operates at a COP of 3.5 for the whole year (give or take negligible variations), and the system involves free cooling of the condensor, should I accept it?

    Thank you!



  2. #2
    Join Date
    May 2012
    Location
    England
    Age
    53
    Posts
    1,220
    Rep Power
    28

    Re: low ambient condenser operation

    Quote Originally Posted by mk2coupe85 View Post
    Hello,

    Hope I can get some help with this concept I am struggling with.

    What happens to the refrigeration cycle at extremely low ambient temperatures. If there is nothing to regulate the system, wouldn't the fluid exit the condenser at an extremely low temperature? And if that were to happen, the refrigeration cycle would not be possible.

    Is there always, without stating it, a system in place (such as an ORI/ORD) that regulates the fluid at the condensor exit (or, more pertinently, expansion valve inlet)? Can I correctly assume this to be the case if I know that the condensor is experiencing free cooling.

    Would the condenser type have an affect on this? Air-cooled vs evap condenser for example?

    In other words, if someone claims that there commercial refrigeration system operates at a COP of 3.5 for the whole year (give or take negligible variations), and the system involves free cooling of the condensor, should I accept it?

    Thank you!

    What tends to happen is the condensing temperature drops to a point
    where the pressure of the liquid in the liquid pipe is not high enough
    for it to force the expansion valve open fully. This then leads to liquid logging
    inside the condenser / receiver and the evap becomes a bit starved of refrigerant.

    It can be controlled by regulating the speed of the cond fan/s and adding
    valves that keep the pressure up in low ambients, but it is a common fault
    with basic systems.

    Regards

    Rob

    .
    .. ... -. .----. - / -- --- .-. ... . / -.-. --- -.. . / --. --- --- -..

  3. #3
    Join Date
    Mar 2009
    Location
    U.S.A.
    Posts
    300
    Rep Power
    12

    Re: low ambient condenser operation

    All of Rob's is correct: but there can be more to it. In a compact system with a fair extent of compressor tolerance and no concerns about oil return or evaporator performance, its exactly what will happen, TXV or Cap Tube or what have you. In the worst cases the evaporating pressure can drop so far that a coil that is just meant for AC will frost and plug up, for instance. But in an expansive system, with oil separators, multiple compressor oil return arrangements, split condenser coils, TXV's with conventional charges trying to pass liquid colder than the Evap Temp and so on: a steady discharge pressure and some operating envelope in terms of the HP liquid temperature, are more like requirements.

    Throw heat recovery arrangements on top of all that and it can really get involved.

Tags for this Thread

Posting Permissions

  • You may not post new threads
  • You may not post replies
  • You may not post attachments
  • You may not edit your posts
  •