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Thread: delta T

  1. #1
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    Confused delta T

    Why we take large delta in condenser as compared to evaporator ?

  2. #2
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    Because the cond coil rejects more heat than the evap coil picks up?

  3. #3
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    to reject more heat size of condenser is kept than evaporator, doesn't understand the logic behind delta T

  4. #4
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    Quote Originally Posted by ddkk0099 View Post
    Why we take large delta in condenser as compared to evaporator ?
    Are you referring to the Delta T (ΔT) or the TD?

    Where:

    The ΔT of the condenser or evaporator is the temperature difference between the entering and leaving air.

    The TD of the condenser is the difference between the saturated condensing temperature and the ambient temperature.

    The TD of the evaporator is the difference between the entering air temperature and the saturated evaporator temperature.

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  6. #5
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    Thread Starter
    I am referring to TD

  7. #6
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    Quote Originally Posted by ddkk0099 View Post
    I am referring to TD
    The TD being greater for the condenser than the evaporator may hold true for the typical commercial refrigeration system such as a walk-in cooler which may have a 20-30F TD and the evaporator only 10-15F TD, however for a typical commercial comfort cooling A/C system the condenser may have a 15-25F TD while the evaporator might be a 35F TD (80F-45F).

    But if I'm getting the basic point to your question, one major reason the condenser size can be kept relatively smaller is you can move a lot more air across a condenser coil since you can run a higher face velocity, like 700-800 FPM as opposed to about 500 FPM for an evaporator.

  8. #7
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    I may be wrong here but, when I asked myself this question years ago, I figured that it was due to the additional heat that is added to the condenser due to the heat of compression from the compressor.

    That is the only thing that sort of made sense to me. I figured that the system designers had to configure the system to reject all the heat that was picked up from the evap plus what was created from the compressor.

    Maybe I was just trying to make sense of it all when I was just starting out in the trade.
    Can someone please explain to me -
    Why is there never enough time to do it right the first time, but plenty of time to do it twice?


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  9. #8
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    I also try correlate condenser extra heat rejection with this , but i guess to reject more heat the size of condenser is keep larger than evaporator.

  10. #9
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    if an evaporator is designed to collect 12,000 btu's, the condenser is generally sized to reject 15,000 btu's.


    the additional heat (3,000 btu's) comes from heat added to the refrigerant by the compressor motor, and the heat of compression.

  11. #10
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    Yes it is ok, but my question was of high TD in condenser in comparison to evaporator.

  12. #11
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    Quote Originally Posted by ddkk0099 View Post
    Yes it is ok, but my question was of high TD in condenser in comparison to evaporator.
    Really, the only time I've seen the condensor running a TD as high as the evap is when the system isn't operating properly. Dirty outdoor coil, bent fins, etc. I guess its higher in heat mode but it shouldn't be in cooling.

  13. #12
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    Quote Originally Posted by Achso017 View Post
    Really, the only time I've seen the condensor running a TD as high as the evap is when the system isn't operating properly. Dirty outdoor coil, bent fins, etc. I guess its higher in heat mode but it shouldn't be in cooling.
    Also, I find the higher SEER systems run lower TD at the condenser than the lower SEER systems.
    Can someone please explain to me -
    Why is there never enough time to do it right the first time, but plenty of time to do it twice?


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  14. #13
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    When it comes to TD's, in virtually all applications above freezing, the evap is the way it is to get a desired humidity. In both HVAC and refrigeration.

    Lower TD's on the condenser side are due to a low load, higher efficiencies, or a combination of the two.
    If you were a real tech, you'd solder a relay on that board and call it good to go.

    I do a triple evac with nitro to remove non condensables.

    I use 56% silver on everything except steel.

    Did you really need the " If you were a real tech " ??

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