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Thread: Static pressure troubles

  1. #21
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    That Air Handler uses an X-13 Constant Torque motor. I believe that .2 Test Static has to do with the air leakage standards the fan coil has to achieve. Refer to the Airflow Performance charts in the install manual.
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  2. #22
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    Thread Starter
    Quote Originally Posted by WAYNE3298 View Post
    Your primary concern should be airflow. You will seldom see design airflow at design static pressure. Run a pitot traverse of the duct and adjust airflow to within design if possible. The recorded measured static will be whatever you measure.
    Measured and adjust upflow from the coil?

  3. #23
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    The best way to measure airflow is pitot traverse of the duct. Second best is measure flow at the diffusers with a flow hood.
    No man can be both ignorant and free.
    Thomas Jefferson

  4. #24
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    Quote Originally Posted by LRB View Post
    I actually reduced the speed. It's a PSC 4 speed motor 3 ton 16x14 return into a 20x16 filter box. Supply is 19x21. I have not tested the velocity yet.
    My Tin Man always insists 20x20 filter grills for 2.5 tons , and all 5 ton units get 2 of the 20x20 filters

    Going by that , a 20x20 is a little too small for yours

  5. #25
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    Is the filtered rack a media cabinet or just a 1? And If it were me I would strongly suggest purchasing a new down drop and filter rack to the customer. 16x20 isnt sufficient for much unit at all. And why is the return drop smaller than the supply? I would suggest a 16x25 media cabinet and a return drop of similar size. That should get it under control. You didnt give any supply vs return static measurements but I assume the return is very high and the supply is low.

  6. #26
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    Where are you measuring your return static and where does the instructions say to measure it at. The point I am getting at is with most furnace applications you measure the return after the filter, but with an air handler you measure it before the filter. I believe this is because most air handlers have a filter built into the bottom and furnaces do not, they are external. The filer alone can add .25 or more static.

  7. #27
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    BNME8EZ you are correct. When the filter rack is built into the unit the external SP includes the filters. When external to the AHU the manufacture doesn't know what filters you will use and cannot include the filter pressure drop with the internal SP.
    No man can be both ignorant and free.
    Thomas Jefferson

  8. Likes Core_d liked this post.
  9. #28
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    How does the TESP balance out? Is it higher on the return side, supply side, or equal? That will give you a clue as to where the problem might be.

    In my region, undersized ductwork is common. Even more common here is undersized R/A intakes. Since the thick pleated filters have taken over the Big Box Store market, most homes have them. I pull those out all day and replace them with the throw-away fiberglass filters, given the undersized intakes.

    When I come across a system with high static, I determine which side it's on, then assess the supply or return ductwork sizing and the intake sizing. Duct sizing charts are your friend if you aren't familiar with the cfms a given duct size will accommodate. If you need a chart, let us know and someone will upload one or post a link.

    Quote Originally Posted by LRB View Post
    I actually reduced the speed. It's a PSC 4 speed motor 3 ton 16x14 return into a 20x16 filter box. Supply is 19x21. I have not tested the velocity yet.
    16x14 intake is entirely too small for 3 tons (as would be 20x16). That is likely the reason for your high static. Or at least one of the reasons.

    The proper method for R/A intake sizing is to measure the open area of the intake and multiply it by two for the number of cfms it will properly support. Then divide that number by 400 for the tonnage.

    Example: 20x20=400 sq in
    Example: x2 = 800 cfms.
    Example: 800 cfms /400 (cfms per ton) =2 tons.

    20x20 will accommodate 2 tons (800 cfms) of airflow. As earlier mentioned, more humid climates do well with 350cfm per ton, since the lower airflow will remove humidity more efficiently.
    Last edited by vin lashon; 06-21-2019 at 10:45 PM.

  10. #29
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    Where did you learn the formula?


    Sent from my iPhone using Tapatalk

  11. #30
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    Quote Originally Posted by Core_d View Post
    Where did you learn the formula?


    Sent from my iPhone using Tapatalk
    Or if you know manufacturer name, and grille model. You can use that data for that grille.

    http://www.hartandcooley.com/assets/...3_661_a661.pdf
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    How-to-apply-for-Professional

    How many times must one fix something before it is fixed?

  12. #31
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    Quote Originally Posted by Core_d View Post
    Where did you learn the formula?


    Sent from my iPhone using Tapatalk
    I believe that this is from filter grill manufacturers, they don't want to see over 2 CFM/sq in. Now how much this changes with a filter at the equipment I don't know. My guess is with a filter grill because the grill is basically against the filter it has less free open area than when the 2 are separated, but again that is only a guess.

  13. #32
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    16x25 is pretty standard in my area as this is the size of most furnaces with a 3ton blower. I dont do resi and Im scared to test mine, out of site out of mind scenario
    Honeywell you can buy better but you cant pay more

    I told my wife when i die to sell my fishing stuff for what its worth not what i told her i paid for it

  14. #33
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    Quote Originally Posted by crazzycajun View Post
    16x25 is pretty standard in my area as this is the size of most furnaces with a 3ton blower. I don’t do resi and I’m scared to test mine, out of site out of mind scenario
    Straight heat?

  15. #34
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    16x25 will work , its just gonna be noisey , and you have to change it regularly

  16. #35
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    Quote Originally Posted by vin lashon View Post
    Straight heat?
    Nope
    Honeywell you can buy better but you cant pay more

    I told my wife when i die to sell my fishing stuff for what its worth not what i told her i paid for it

  17. #36
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    I change my air filter regularly. Once or twice a year.


    Quote Originally Posted by Snapperhead View Post
    16x25 will work , its just gonna be noisey , and you have to change it regularly
    I do a triple evac with nitro to remove non condensables.

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