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  1. #1
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    Overcharging of Refrigerant



    Dear Friends ,

    Does the overcharging of refrigerant in system has any negative effect on the cooling of system.I have heard that overcharging leads to decrease in cooling , is it right or wrong and please suggest the reasons supporting your answer.

    I hope my seniors will help me in resolving the above said issue.

    Thanks for your cooperation.


    Kind Regards
    Sumit



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    Re: Overcharging of Refrigerant

    .

    It depends on the system.

    If it is direct expansion with a liquid reciever then you can put as much liquid in untill
    you reach the capacity of the reciever. Then when it is overcharged where will the excess
    pressure go?

    It will either pass to the evaporator which will then increase the evaporating temperature
    which will then cause the system to run at higher temps and pressures. Ultimately resulting
    in a failure some where.

    If the overcharge is too much then the system may fail and release all the refrigerant to atmosphere.

    If the system is a capilary tube then over charging will result in liquid flooding back to the comp.

    All the best

    taz

    .

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    Re: Overcharging of Refrigerant

    Hi Taz ,

    Thanks for your prompt reply.You explained very well that how can a system fail due to overcharging.But number of times , either chiller or Air Conditioner works when the gas is overcharged up to certain limit.

    My question is , how overcharging of refrigerant in the chiller or Air conditioning (window,split,Automobiles) effects their cooling efficiency ?? What change occur in the various parameters that leads to decrease in efficiency of system.

    Thanks for your cooperation.Looking forward for your answers.

    Cheers

    Sumit

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    Re: Overcharging of Refrigerant

    Hello,
    Your system will be designed to run at specific temperatures and pressures and by adding more refrigerant than needed, you would be altering these. The system running pressures would then be increased which in turn would increase the temperatures, altering super heat and head pressure, you also risk flushing the oil from the compressor from liquid flooding back, which will damage the compressor, the system may not also run as it could go out on H.p switch and you would also be increasing electrical bills.

    Regards Paul.

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    Re: Overcharging of Refrigerant

    Quote Originally Posted by Hobair View Post
    Hello,
    Your system will be designed to run at specific temperatures and pressures and by adding more refrigerant than needed, you would be altering these. The system running pressures would then be increased which in turn would increase the temperatures, altering super heat and head pressure, you also risk flushing the oil from the compressor from liquid flooding back, which will damage the compressor, the system may not also run as it could go out on H.p switch and you would also be increasing electrical bills.

    Regards Paul.
    Paul, your theory only stands for systems with cap tubes.
    Last edited by Peter_1; 01-01-2012 at 01:58 PM.
    It's better to keep your mouth shut and give the impression that you're stupid than to open it and remove all doubt.

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    Re: Overcharging of Refrigerant

    Yes you mean the flushing of the oil right? The compressor can still be damaged from overcharging. Also the pressures and temperatures would be changed from over charging, altering your super heat, evaporator and air off temperatures into the area to be cooled, even if you had a TEV on unit this size, maybe on a larger system with liquid line receiver you could loose some of this excess refrigerant. The systems sumit is talking about should have the specific charge recommended by the manufacturer.

  7. #7
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    Re: Overcharging of Refrigerant

    Thanks Hobair and Peter ,

    Like Taz you also explained how the system can fail due to overcharging of refrigerant.But my question was if the overcharging is not up to that extent which leads to failure of system , it just decreases the efficiency of chiller.

    According to me, condensers are designed to handle a particular volume of refrigerant and a fixed volume of water (in case of water cooled) in GPM should be flowed in pipes for proper heat exchange.But if the refrigerant is overcharged, there will be more volume of refrigerant in condenser due to which less HEAT EXCHANGE.So the less cooled liquid will go to expansion valve and evaporator which decreases the efficiency of system.

    In short, I can say " Under-sizing " of condenser.

    This is my opinion , I hope my seniors are the better judge.They will tell whether its wrong or right.

    Looking forward for replies.

    Cheers

    Sumit

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    Re: Overcharging of Refrigerant

    Hi Sumit,

    Yes you are right you are putting too much duty on the condenser, but also too much duty on other components such as the evaporator, this may be getting to much liquid and be flooded, hence removing less heat from the area to be cooled , as a result of this you may get liquid to the compressor, the compressor will not pump liquid. As i said earlier this will increase the energy consumption of your system and decrease the efficiency of your system.

    You are basically altering the whole design of the system, I used to work for a Heat pump manufacturer here in the uk, the manufacturer has specifically stated the refrigerant charge and has probably put a lot of research into finding the correct refrigerant charge to run this system efficiently.
    Regards Paul.

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    Re: Overcharging of Refrigerant

    Hi Paul ,

    Thanks for your prompt replies.Its clear to me now.Can you please provide my any material related to heat pumps , any manuals or other material.I do not have idea about them as I have only worked on chillers.

    Cheers
    Sumit


    " The mind always fail first, not the body "

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    Re: Overcharging of Refrigerant

    Hi Sumit,

    You're welome, finished for Christmas now so plenty of spare time. I do not have any way of sending you manuals, but there are plenty of websites on line with manuals to download, take a look at these websites this may help you http://www.inspectapedia.com/aircond/aircond15j.htm http://www.airconwarehouse.com/acatalog/More_Info.html

    R
    egards Paul

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    Re: Overcharging of Refrigerant

    Hi Paul,

    Thanks for the links.No Christmas holidays in India especially for poor people working with private contractors.Christmas is on sunday, thats why there will be a holiday otherwise no chance brother.

    I hope you are having a great time there.

    Cheers
    Sumit

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    Re: Overcharging of Refrigerant

    Hi Sumit,
    On Chillers depending on the type of compressor, expansion device and condenser an overcharge will cause the system to be less efficient. I will add to this the reasons when I return from work today. When I worked at a chiller specialist they used to trim the charge on large chillers depending on the season. In winter more refrigerant was required. From experience current draw increases with the charge. If we take it to extreme overcharge and look at the effects we will have a better idea. A typical recip chiller with water cooled condenser will fill with liquid leaving less space for condensing so the head pressure will increase this will cause the current to increase as there is a higher pressure for the compressor to pump against, The subcooling will decrease, the refrigerant passing through the expansion device will have to cool it self down more with more flash gas just after expansion leaving less space in the cooler for refrigerant to cool the water. If there is a reciever which is separate like on a rack system there is a little more room for fluctuating refrigerant levels or overcharge. Most aircooled or water cooled chillers do not have a receiver the excess refrigerant banks up in the condenser.
    On larger systems with receivers we should charge to only maintain a liquid seal the the expansion device under normal conditions of operation, but most of us add a little extra.
    Last edited by Tesla; 22-12-2011 at 09:59 PM.

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    Re: Overcharging of Refrigerant

    Thanks Tesla and other members.Its clear to me now.Thats why I love this website.


    Cheers
    Sumit

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    Re: Overcharging of Refrigerant

    Quote Originally Posted by Tesla View Post
    Hi Sumit,
    ..... The subcooling will decrease, the refrigerant passing through the expansion device will have to cool it self down more with more flash gas just after expansion leaving less space in the cooler for refrigerant to cool the water. .....
    SC will increase, not decrease.
    It's better to keep your mouth shut and give the impression that you're stupid than to open it and remove all doubt.

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    Re: Overcharging of Refrigerant

    Thanks Peter,

    But can you please explain how Sub-cooling will be increased ? According to Tesla overcharging of refrigerant decreases the sub-cooling. Even, I think due to " under - sizing " of condenser; SC will be decreased.

    Thanks for your cooperation and Happy New Year


    Cheers

    Sumit

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    Re: Overcharging of Refrigerant

    Sumit.

    First we need to agree that sub cooling is the differential between the temperature at which all the gas has been cooled in to a liquid without any vapour residue and the actual temperature of the liquid.

    Now imagine the condensor as a single long pipe.
    In one end of the pipe we inject hot superheated gas, across the outside of the pipe we spray cold water and at the other end we monitor what's happening...
    As the superheated vapour travels down the pipe it will cool down and liquid will start to form in the vapour, at some point the mixture will get cold enough so that it is only liquid and no vapour.
    But... The pipe doesn't end there, the liquid travels further inside the pipe and continues to cool down until it leaves this cooled pipe, that additional temperature drop is your sub cooling.

    Now, if you add more liquid to a system than it can handle then the only place for it to accumulate is in the condensor.
    If you again visualise our long pipe condensor, what this will do is to increase the length of pipe the liquid has to flow through before leaving the pipe therefore increasing the additional temperature drop, thus increasing the sub cooling.

    But it doesn't end there...
    As the pipe length available to cool the superheated vapour in effect has been shortened, the condensor's efficiency will be reduced (can't do the same job with less length, ask any woman!) therefore your head pressure will increase.
    For the head pressure to increase, more energy is needed or lees duty will be delivered.
    There is your drop in efficiency.

    Last edited by The Viking; 04-01-2012 at 08:15 PM.

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    Re: Overcharging of Refrigerant

    Thanks for the explanation Viking.I must say very well explained by you. But I hope you will not mind in briefly explaining the following two lines

    " Now, if you add more liquid to a system than it can handle then the only place for it to accumulate is in the condenser.
    If you again visualise our long pipe condensor, what this will do is to increase the length of pipe the liquid has to flow through before leaving the pipe therefore increasing the additional temperature drop, thus increasing the sub cooling. "

    By first line, you mean that accumulation of overcharged refrigerant is usually takes place at condenser.And the second and the most important factor behind the increase in Subcooling is still not clear.

    I hope you will explain it again " If you again visualise our long pipe condensor, what this will do is to increase the length of pipe the liquid has to flow through before leaving the pipe therefore increasing the additional temperature drop, thus increasing the sub cooling. "

    Thanks for your cooperation

    Cheers

    Sumit

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    Re: Overcharging of Refrigerant

    No worries,
    Let's say that this pipe condensor is 10 m long, correctly charged all vapour will become liquid after 9 m and the last m is providing the subcooling (required to ensure the metering device receives pure liquid).

    Now if you add, say Xkg of additional refrigerant then that will take up another m of the condensor, hence the liquid now has to travel 2 m from where it formed to where it leaves the pipe.
    The longer the liquid travels in this cold pipe the greater the temperature differential will be. This also would leave the vapour with only 8 m to cool down in.

    Now, if you continue to add refrigerant then at some point you will be left with too short pipe length for the vapour to cool down in and something has to break. Hopefully whoever built this system fitted a HP switch that stoppes the compressor before any serious damage is caused.
    Last edited by The Viking; 06-01-2012 at 01:51 AM. Reason: Poor englis

  19. #19
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    Re: Overcharging of Refrigerant

    http://www.fridgetech.com/miscellany...er/mollier.swf
    Sorry I use this source but anyhow, it's well made.
    It's better to keep your mouth shut and give the impression that you're stupid than to open it and remove all doubt.

  20. #20
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    Re: Overcharging of Refrigerant

    If a system is seriously overcharged the evaporating temperature increases, there is not enough room in the system for all the liquid so it fills the evaporator (and condenser) stopping the evaporating temperature getting low enough to do much duty, especially as the room or product gets nearer the evaporating temp.

    In the end little heat is absorbed in the evap and little heat is given off in the condenser as the system almost just ends up pumping liquid around.

    I hope that makes sense...
    Mostly found in Oxfordshire, UK :)

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    Re: Overcharging of Refrigerant

    Another clarification...
    (I edited my previous post in an attempt to improve the poor english but...)

    As some of you asked in messages, I will elaborate a bit further,

    I deliberately used the terms "temperature differential" and "sub cooling" instead of "temperature" in my post above.
    The reason for this is simple, the temperature will vary as it is dependant on the pressure whilst the temperature differential (or sub cooling) stays roughly constant as long as nothing else changes.


    To go back to my example above;
    Say that when the system is correctly charged the (high) pressure is 15 Bar, the temperature where all the vapour has become liquid is then 42*C and the liquid is leaving the condensor is at 36*C.
    This gives a sub cooling of 6K.

    Now if we add more refrigerant to this then the likely result is something like;
    High pressure at 17.5 Bar, the temperature where all the vapour has become liquid is then 48*C and the liquid will leave the condensor with a temperature of 36*C.
    This would give a sub cooling of 12K even as the liquid line temperature as it leaves the condensor hasn't changed at all.

    And maybe someone then lowers temperature of the water that is cooling our condenser in order to reduce the pressure back to 15 Bar, then we would end up with;
    High pressure at 15 Bar, the temperature where all the vapour has become liquid is just as when we started 42*C but this time the liquid will leave the condensor with a temperature of 30*C.
    Keeping the sub cooling at 12K but now the liquid line temperature as it leaves the condensor has dropped significantly.

    This is also why it is so important to look at both pressures and temperatures when we are trying to figure out what is going on inside a system.


    I'm off to bed now...

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    Re: Overcharging of Refrigerant

    Thanks Viking and monkey spanners.. I must appreciate your way of explaining the fundamentals by using suitable examples.I will never forget the above discussed issue.

    Thanks Peter for the useful link and thanks to Monkey spanners also.

    I hope you are having a great weekend.


    Cheers

    Sumit

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    Re: Overcharging of Refrigerant

    Sorry Sumit, Viking, Monkey Spanners & Peter for my incomplete understanding and thank you for putting it right, I could not find very clear info on this topic.

  24. #24
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    Re: Overcharging of Refrigerant

    Hi Tesla,

    No worries, thanks for your participation.I must say thanks to Peter who noticed it.

    Cheers

    Sumit

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