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  1. #14
    Join Date
    Mar 2013
    Location
    Maine
    Posts
    486
    Quote Originally Posted by itaintme View Post
    EXPERIENCE AND GOOD TRAINING ARE HOW I LEARNED. sorry ..cap stuck for a sec.

    SC is listed on unit name plate. Super heat can be be obtained reasonably successfully using a refrig charging card.
    I was talking refrigeration equipment or package roof top units. your talking resi splits i take it?

  2. #15
    Join Date
    Aug 2007
    Location
    Edmond, Oklahoma
    Posts
    396
    Quote Originally Posted by Sgt. Dookie View Post
    Should the condenser air temp split be an important thing to check during a maintenance?
    Yes. It tells you about the airflow through the coil.

  3. #16
    Join Date
    Aug 2007
    Location
    Edmond, Oklahoma
    Posts
    396
    Quote Originally Posted by Sgt. Dookie View Post
    But the surface area of the condenser is much larger, therefore the split will be less. Maybe half? 8-10? I just don't know if this number is valuable in a troubleshooting situation or not
    There are factors other than surface area that affect the heat transfer rate from the coil. Airflow is one of those factors. Coefficient of heat transfer of the coil surface (which can be affected by dirt) is another.

    If the split is too high, it usually means there's not enough airflow through the coil. Which usually means it's dirty and/or clogged up.

  4. #17
    Quote Originally Posted by bobster View Post
    Yes. It tells you about the airflow through the coil.
    That's true but the OP was asking about using 30* above ambient as a way to as a determination of proper system operation of a tuned system For trouble shooting the temp rise off the condenser is a must-do.

  5. #18
    Join Date
    Aug 2007
    Location
    Edmond, Oklahoma
    Posts
    396
    Quote Originally Posted by itaintme View Post
    That's true but the OP was asking about using 30* above ambient as a way to as a determination of proper system operation of a tuned system For trouble shooting the temp rise off the condenser is a must-do.
    Really? Here's what I read that he said:

    "Books say condensing pressure should be ambient temp (in my original question, the incoming air temp) plus 30 degrees. In reality I've seen 20 or so degrees normally. But that's not what I'm asking.. I wonder about the incoming air vs leaving air temp."

    My understanding of his question(s) was he wanted to know of what value the air temperature rise across the condenser coil was.

  6. #19
    Quote Originally Posted by bobster View Post
    Really? Here's what I read that he said:

    "Books say condensing pressure should be ambient temp (in my original question, the incoming air temp) plus 30 degrees. In reality I've seen 20 or so degrees normally. But that's not what I'm asking.. I wonder about the incoming air vs leaving air temp."

    My understanding of his question(s) was he wanted to know of what value the air temperature rise across the condenser coil was.
    And my intent was meant to say: There are many varied opinion on what the condenser discharge temp over ambient should be. I have heard values of 10*F to 35*F over ambient that were big used by techs despite the age or efficiency of the system.

    A rule of thumb with such a wide spread is not good practice.
    And as I stated there are to many variables to consider to make it useful.

    Case in point: Would you charge a unit to 30*F over ambient on a 70* day with low IDWB?.

    This is why I am against most rules of thumb.

  7. #20
    Join Date
    Aug 2007
    Location
    Edmond, Oklahoma
    Posts
    396
    Quote Originally Posted by itaintme View Post
    And my intent was meant to say: There are many varied opinion on what the condenser discharge temp over ambient should be. I have heard values of 10*F to 35*F over ambient that were big used by techs despite the age or efficiency of the system.

    A rule of thumb with such a wide spread is not good practice.
    And as I stated there are to many variables to consider to make it useful.

    Case in point: Would you charge a unit to 30*F over ambient on a 70* day with low IDWB?.

    This is why I am against most rules of thumb.
    I don't think of it as a "rule of thumb". It is a design parameter. Q = u * A * TD. 30 to 35F for standard efficiency condensers, 20 to 25F for higher efficiency equipment (bigger coils).

    If you get no useful information from it, don't use it, but that's what it is used for, which was the question.

    As to your question, I would never charge using condenser temperature split. I use SH or SC depending on the metering device.

  8. #21
    Join Date
    Jun 2001
    Location
    Moore, Oklahoma, United States
    Posts
    4,292
    Quote Originally Posted by bobster View Post
    I don't think of it as a "rule of thumb". It is a design parameter. Q = u * A * TD. 30 to 35F for standard efficiency condensers, 20 to 25F for higher efficiency equipment (bigger coils).

    If you get no useful information from it, don't use it, but that's what it is used for, which was the question.

    As to your question, I would never charge using condenser temperature split. I use SH or SC depending on the metering device.
    The chart below shows about a 355 (108F) condenser pressure @ 95 outdoor. 13 degree difference. Delta T coming from condenser would have to be even less...
    Attached Images Attached Images  

  9. #22
    Join Date
    Aug 2007
    Location
    Edmond, Oklahoma
    Posts
    396
    Quote Originally Posted by 54regcab View Post
    The chart below shows about a 355 (108F) condenser pressure @ 95 outdoor. 13 degree difference. Delta T coming from condenser would have to be even less...
    Right, indicating an even higher efficiency coil. If manufacturer's data is available, I certainly use it.

  10. #23
    [QUOTE=bobster;
    As to your question, I would never charge using condenser temperature split. I use SH or SC depending on the metering device.[/QUOTE]

    neither would I.
    Was trying to show how misused bad rules of thumb get and charging an ac was the best example I can think of . There are guys who charge to 30* over ambient on high seer equipment. They use the same number to check for good system operation using that same 30*.

  11. #24
    Join Date
    Aug 2007
    Location
    Edmond, Oklahoma
    Posts
    396
    Quote Originally Posted by itaintme View Post
    neither would I.
    Was trying to show how misused bad rules of thumb get and charging an ac was the best example I can think of . There are guys who charge to 30* over ambient on high seer equipment. They use the same number to check for good system operation using that same 30*.
    Gotcha

  12. #25
    Join Date
    Aug 2009
    Location
    Jurupa Valley, CA
    Posts
    1,781
    the split is going to be dependent on the air flow over the coil, more than anything else. In essence, air flow * temp split = heat rejection. Higher air flow means lower temp splits, and in most cases, better heat rejection, and less work by the compressor. There is, by far, no 'thumbrule' that will work for every condenser though.

  13. #26
    Quote Originally Posted by bobster View Post
    Gotcha
    !@#$%%....what the heck?

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