Page 1 of 21 1234567811 ... LastLast
Results 1 to 13 of 266
  1. #1
    Join Date
    Jul 2004
    Posts
    68
    can you correctly check subcooling with a reciever in the circuit on small systems? from a hvac point of view, checking subcooling with recievers is not very common from what i've been told.

  2. #2
    Join Date
    Sep 2002
    Location
    South Dakota
    Posts
    6,579

    Refrigerant in a receiver is always in a saturated condition. You have a mixture of liquid and vapor just like you have in a refrigerant cylinder. So, it is in a saturated condition not subcooled.

    When subcooled refrigerant enters the receiver you lose any subcooling you had. That is why you measure your subcooling BEFORE the receiver when charging by subcooling.

    You will get some subcooling back in the liquid line on the way to the metering device.


  3. #3
    Join Date
    Jul 2000
    Location
    Guayaquil EC
    Posts
    10,460
    Originally posted by NormChris
    Refrigerant in a receiver is always in a saturated condition. You have a mixture of liquid and vapor just like you have in a refrigerant cylinder. So, it is in a saturated condition not subcooled.
    This is an old myth. Comparing the conditions in a receiver of an operating system to those of a refrigerant cylinder is like apples and oranges. The receiver is part of a dynamic system whereas the cylinder is static and confined.

    Originally posted by NormChris
    When subcooled refrigerant enters the receiver you lose any subcooling you had. That is why you measure your subcooling BEFORE the receiver when charging by subcooling.
    If a receiver has subcooled liquid entering, the only things that can cause a loss of subcooling is a drop in pressure and/or an increase in temperature......the liquid refrigerant will not lose subcooling solely due to the presence of vapor.

    Originally posted by NormChris

    You will get some subcooling back in the liquid line on the way to the metering device.
    How does this happen? You can't raise the pressure (unless you have an LPA), so it has to be a drop in liquid temperature......right?

  4. #4
    Join Date
    Sep 2002
    Location
    South Dakota
    Posts
    6,579

    I have participated in many discussions over this over the years. I have discussed this with a number of engineers and have heard arguements from educated people who disagree with each other. I have read literature from Trane, Carrier and Copeland that contradict each other.

    The best way to solve it is to operate a system and plot it on a Mollier Diagram.

    Just for kicks, I just sent this as a question in an e-mail to Hy-Save and asked them to explain it.


  5. #5
    Join Date
    Sep 2002
    Location
    South Dakota
    Posts
    6,579
    Originally posted by icemeister
    Originally posted by NormChris
    Refrigerant in a receiver is always in a saturated condition. You have a mixture of liquid and vapor just like you have in a refrigerant cylinder. So, it is in a saturated condition not subcooled.
    This is an old myth. Comparing the conditions in a receiver of an operating system to those of a refrigerant cylinder is like apples and oranges. The receiver is part of a dynamic system whereas the cylinder is static and confined.

    Originally posted by NormChris
    When subcooled refrigerant enters the receiver you lose any subcooling you had. That is why you measure your subcooling BEFORE the receiver when charging by subcooling.
    If a receiver has subcooled liquid entering, the only things that can cause a loss of subcooling is a drop in pressure and/or an increase in temperature......the liquid refrigerant will not lose subcooling solely due to the presence of vapor.

    Originally posted by NormChris

    You will get some subcooling back in the liquid line on the way to the metering device.
    How does this happen? You can't raise the pressure (unless you have an LPA), so it has to be a drop in liquid temperature......right?
    If you are right then a temperature-pressure saturation chart will not work a the receiver.

  6. #6
    Join Date
    Jul 2000
    Location
    Guayaquil EC
    Posts
    10,460
    Norm, when I saw this question posted I said to myself....."Here we go again!".

    Why do you say the charts wouldn't work? The info the P/T charts gives you relate to saturated conditions. You know you have subcooled liquid entering by the pressure and the temperatures you measure. You know you have subcooled liquid leaving the receiver by the pressure and temperature you measure. The "saturated liquid in a receiver" theory says that this liquid magically loses all its subcooling after entering the tank and then somehow gets it back after it leaves. What physical laws allow for this to happen?

    Let's say that I measure the pressure and temperature of the liquid in an R22 receiver as 210 psig and 95 Deg F. The P/T chart would tell me that the saturation temperature at 210 psig is 105 Deg, so the liquid in that receiver is 10 Deg subcooled. The "theory" states this cannot possibly exist. I've measured it and it does exist.

    Another way of looking at this is that with the logic of this "theory" one would expect that if there were in fact subcooled liquid in the receiver it would have to be 100% full by definition. Again, by field observation I know this also not to be true.

    Let's get some measurements in here so we can put this issue to rest.

    [Edited by icemeister on 07-18-2004 at 04:11 PM]

  7. #7
    Join Date
    Apr 2002
    Location
    Dallas, TX
    Posts
    2,987
    This discussion reminds me of a previous thread where we were arguing if subcooling increases when the condenser gets dirty... To reiterate my opinion: yes, if you have a TEV as the metering device.

    I have to side with icemeister on this one. Granted, if you have a vapor-liquid interface in the receiver, you must be at saturation. But I can envision in a dynamic system where you can lose this interface if you have sufficiently subcooled refrigerant from the condenser.

    For subcooled refrigerant to return to saturation in the receiver either: (1) pressure must be reduced in the receiver, and/or (2) the receiver absorbs sufficient heat to eliminate the subcooling.

  8. #8
    Join Date
    Sep 2002
    Location
    South Dakota
    Posts
    6,579
    Originally posted by Andy Schoen
    This discussion reminds me of a previous thread where we were arguing if subcooling increases when the condenser gets dirty... To reiterate my opinion: yes, if you have a TEV as the metering device.

    I have to side with icemeister on this one. Granted, if you have a vapor-liquid interface in the receiver, you must be at saturation. But I can envision in a dynamic system where you can lose this interface if you have sufficiently subcooled refrigerant from the condenser.

    For subcooled refrigerant to return to saturation in the receiver either: (1) pressure must be reduced in the receiver, and/or (2) the receiver absorbs sufficient heat to eliminate the subcooling.

    Andy, I was hoping you would jump in on this topic. I am still thinking this through and I appreciate yours and ices input. What bothers me is that I have read and heard positions and arguments both ways from several sources that should be authorities. Manufacturers and HVAC engineers who design and build this stuff. It is easy to get involved in a circular argument on this one.


  9. #9
    Join Date
    Jan 2004
    Location
    Earth
    Posts
    4,879
    I thought that refrigerant in a tank can only become saturated after it becomes static and equalizes with ambient. Otherwise how would you know if it's condensing or evaporating?

    Don' mind me I get confused easily.

    [Edited by frozensolid on 07-18-2004 at 09:12 PM]
    A Diamond is just a piece of coal, that made good under pressure!

  10. #10
    Join Date
    Jul 2004
    Posts
    68
    Just checked back in. Thanks for the replys. It seems there is alot of ways to look at this. I do understand all of your replys and it also seems more info may be needed to put this question to rest. If something else is found please let me know. Thanks again.

  11. #11
    Join Date
    Apr 2002
    Location
    Dallas, TX
    Posts
    2,987
    Originally posted by NormChris
    What bothers me is that I have read and heard positions and arguments both ways from several sources that should be authorities. Manufacturers and HVAC engineers who design and build this stuff. It is easy to get involved in a circular argument on this one.
    I hear you as I've heard the same arguments. But I think the confusion arises from the static versus dynamic conditions. With a static condition, it's a no-brainer. A liquid-vapor interface must exist in the receiver and thus we must have saturation.

    But the First Law must be obeyed, and we put things in motion, it is my opinion you should be able to deliver enough subcooled liquid to the receiver to prevent a liquid-vapor interface from forming. It is simply a case of subcooling overcoming any pressure loss or heat transfer with the refrigerant flow on its way and at the receiver.

    From a practical standpoint, we're unlikely to find much subcooling leaving the receiver with most systems. Even with systems having flooded head pressure control operating under low ambient temperatures, the hot gas pressurizing the receiver should bring things close to saturation. BTW, when rating head pressure control valves, we assume a saturated condition in the receiver, not that it would change valve ratings much if we assumed a subcooled state in the receiver.

  12. #12
    Join Date
    Jun 2001
    Location
    Michigan
    Posts
    12,077
    Originally posted by icemeister
    Originally posted by NormChris
    Refrigerant in a receiver is always in a saturated condition. You have a mixture of liquid and vapor just like you have in a refrigerant cylinder. So, it is in a saturated condition not subcooled.
    This is an old myth. Comparing the conditions in a receiver of an operating system to those of a refrigerant cylinder is like apples and oranges. The receiver is part of a dynamic system whereas the cylinder is static and confined.

    Originally posted by NormChris
    When subcooled refrigerant enters the receiver you lose any subcooling you had. That is why you measure your subcooling BEFORE the receiver when charging by subcooling.
    If a receiver has subcooled liquid entering, the only things that can cause a loss of subcooling is a drop in pressure and/or an increase in temperature......the liquid refrigerant will not lose subcooling solely due to the presence of vapor.

    Originally posted by NormChris

    You will get some subcooling back in the liquid line on the way to the metering device.
    How does this happen? You can't raise the pressure (unless you have an LPA), so it has to be a drop in liquid temperature......right?
    Hold on a second here now. You can subcool further as it leaves the receiver. easily.

  13. #13
    Join Date
    Dec 2003
    Posts
    2,425
    How about checking subcooling before the receiver? This will tell you what is happening in the condenser, which is what you want to know.

Page 1 of 21 1234567811 ... LastLast

Posting Permissions

  • You may not post new threads
  • You may not post replies
  • You may not post attachments
  • You may not edit your posts
  •  
Comfortech Show Promo Image

Related Forums

Plumbing Talks | Contractor Magazine
Forums | Electrical Construction & Maintenance (EC&M) Magazine
Comfortech365 Virtual Event