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  1. #1

    Question Approach Temperature and fouling

    I am looking for an official document quantifying the increase in approach temperature due to the increase in fouling factor. Was there such a thing published?

  2. #2
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    Lennox might know. They used approach temp for charging. Most manufacturers used subcooling.

    I always looked at head pressure, condensing temperature - Ambient temperature = Condenser split. If the system has a performance chart, high head often indicates fouling whether the system is air or water cooled. (OK, providing a lot of other bad things aren't the problem...) Lower than normal condenser TD will accompany high head if it is fouling. Close to normal can be too close to call. Bad fouling = easy call.
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  3. #3
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    IF you could get the heat exchanger perfomance selection, it will be clearly shown right on there, but since its probably a chiller thats been in for a while, no one will know anything, its just the way things go. If you ever sized a heat exchanger, thats one of the items you select, desired approach. obviously the closer the approach, the larger the exchanger. a few degrees is typical.

  4. #4
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    I don't remember appoach in the context of chillers. Refresh my memory.
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  5. #5
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    Quote Originally Posted by Henri J M View Post
    I am looking for an official document quantifying the increase in approach temperature due to the increase in fouling factor. Was there such a thing published?
    Or you could be losing charge?

  6. #6
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    Quote Originally Posted by flange View Post
    IF you could get the heat exchanger perfomance selection, it will be clearly shown right on there, but since its probably a chiller thats been in for a while, no one will know anything, its just the way things go. If you ever sized a heat exchanger, thats one of the items you select, desired approach. obviously the closer the approach, the larger the exchanger. a few degrees is typical.
    I have never seen approach asked when replacing a heat exchanger. I always been asked number of passes, gpm, and td.

  7. #7
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    It makes a difference. A plate heat exchanger will typically have a closer approach than a tube heat exchanger.

  8. #8
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    To the OP....can increased approach be due to a fouling heat exchanger....sure. But so can can undercharged and poor water flow.

  9. #9
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    Quote Originally Posted by ascj View Post
    I have never seen approach asked when replacing a heat exchanger. I always been asked number of passes, gpm, and td.
    'approach' is probably not the wording that you typically see in selection software...'fouling' is the typical wording. if you don't specify it, then the application engineer SWAGGED it. for chillers, 0.00010 is typical for the evaporator and 0.00025 is usually used for the condensers. units of measurement are in: hr*ft^2*F / BTU

    the OP discussed fouling versus approach. you can not discuss approach temperatures in relation to fouling factor unless you are speaking of a specific machine. in other words, you need to know the approach temperature with a 0.00000 fouling factor. then, you might be able to get close, but i do not believe that you will find a published document other than, 'as the fouling factor increases, so does the approach temperature'.
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