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  1. #1
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    Fan Field Test Accuracies

    For those interested below are some of the fan field test accuracy expectations by AMCA calculated to two standard deviations (95%). I'm not trying to change anyone's mind but this and experience should explain where I'm coming from on some threads.
    I am no longer going to make comments on this subject because I realize if you have a standard way of determining airflow you want to stick with it and that doesn't bother me. I just feel like all my comments do is muddy the waters and right or wrong I don't want to do that.

    Wet Bulb Depression uncertainty = 5 to 10 F

    Fan Speed = 0.5 to 1.0%

    Power Input = 3.0 to 7.0%

    Pitot Traverse = 1.5 to 7.0%

    Static Pressure = 12.5 to 29%

    The expectations take into account most field conditions encountered but it is noted no test data can be obtained if air swirl exists.

  2. #2
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    I'd rather you keep muddying the waters.

    How else are we going to learn ?

  3. #3
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    Please don't stop commenting Wayne. Your input increases our knowledge and opens up new areas.

    For example, it is good to know that air measurement is difficult. It clears up why one can measure static or other parameters, yet the other numbers don't fall into place.

    I value your input. I'm sure others do too.

    The data you posted above is eye-opening. WB for instance. How is that error determined? It does make one pause and wonder how can I ever be accurate?

    On the other hand, it can push one to strive for more readings and higher accuracy.

    Sent from my SM-G930V using Tapatalk

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  5. #4
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    Thread Starter
    BBeer,
    I don't think I have helped anyone but think the person asking the question ends up not knowing what to believe. In fact I have unintentionally pissed off a few people. I wrote specifications for many years and developed a writing style that was direct and to the point. After that I did TAB reports which had to be done the same way. I have tried to temper that here but probably haven't been successful. I don't get up every morning and try to figure out who I want to piss off.

  6. #5
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    If people are getting upset when you present facts, that's on them, not you.

    Personally, I think you are a valuable asset to this forum.


    Quote Originally Posted by WAYNE3298 View Post
    BBeer,
    I don't think I have helped anyone but think the person asking the question ends up not knowing what to believe. In fact I have unintentionally pissed off a few people. I wrote specifications for many years and developed a writing style that was direct and to the point. After that I did TAB reports which had to be done the same way. I have tried to temper that here but probably haven't been successful. I don't get up every morning and try to figure out who I want to piss off.

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  8. #6
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    Thread Starter
    icy,
    The wet bulb depression is for air handling equipment and considers thermometer accuracy, precision (ability to read the scale accurately), single point measurement and the big one stratification. The accuracy they gave can be improved if you do a weighted temperature traverse but that takes so long it isn't worth it. In 20 years I had one client that knew what it is and wanted one. It was bogus because he wanted the temperature weighted using the velocity grid at the cooling coil. The way I obtained wet bulb at the coil discharge was measuring dry bulb temperature right on the coil. There is no evaporation required because the air is saturated. If you are very careful you can get the accuracy error most of the time down to about 2 degrees but only if there is no stratification.
    You can get a pretty good idea of how accurate your wet bulb is by doing a heat balance using enthalpy.

  9. #7
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    You've mentioned heat balance a couple times in the last 2 days. I don't know what that is or maybe I do under another name. Could you elaborate?

    Sent from my SM-G930V using Tapatalk

  10. #8
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    Thread Starter
    Heat balance compares the system design heating or cooling capacity to the actual. The system airflow is measured and the temperatures. Calculate the actual BTUH and compare it to the design. If you measure airflow by pitot traverse and the airflow and temperature are at design your calculated BTUH will be pretty close to design. The reason I mentioned it is that if you calculate airflow using static pressure which I know to be iffy and the design and calculated BTUH are way off something is wrong and it is probably the calculated airflow. One reason I did that was if problems developed I didn't want the engineer to do the calc and think I lied on the report. I heat balance every water coil because I have found a lot of them supplied wrong. The water side and air side should be close.

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  12. #9
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    Thanks Wayne. I guess in my head I call that a capacity check. Thanks again.

    Sent from my SM-G930V using Tapatalk

  13. #10
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    Thread Starter
    icy,
    That's what it is but you are checking the tested capacity against the design capacity. If the field measured airflow is wrong the design and actual capacities will not match.

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