Page 2 of 3 FirstFirst 123 LastLast
Results 14 to 26 of 36
  1. #14
    Join Date
    Dec 2012
    Location
    columbus, OH
    Posts
    6,779
    Post Likes
    Quote Originally Posted by BBeerme View Post
    That test static number looks like something they use at the factory to get the rated capacity out of the unit. So, and I am assuming here, that means your numbers change as the static increases.

    But that's not always as bad as it may seem. Because, if I'm not mistaken, as the airflow decreases, the sensible load decreases and the latent load increases. So if you are in a high humidity area, it could actually be beneficial.

    I welcome others to add or correct me if I'm wrong.

    Where I live, we very rarely have "too high of humidity's", so a restricted airflow like that would really cut down on the capacity of the unit. Just means you're gonna be paying for it to run longer.
    Yea like I said most blower performance charts go to .8 or .9. Even that is really not acceptable in most real life scenarios but over 1 can cause all kinds of problems.


    Sent from my iPhone using Tapatalk

  2. #15
    Join Date
    May 2015
    Location
    Northern Virginia
    Posts
    34
    Post Likes
    Thread Starter
    Thanks for the info, I just ordered a new recliner...........

  3. #16
    Join Date
    Dec 2014
    Posts
    2,557
    Post Likes
    I might be totally misunderstanding your original post @LRB so ignore this if it doesnt pertain.

    Maybe this just pertains to commercial, but

    ....you can have high static from too much airflow.

    You can have high static from too restrictive ductwork..resulting in too little airflow.

    So your system.
    If you are measuring say TESP of 0.9 but you dont know the actual cfm....well then, is the measured "high" static from too much air, or from restrictive ductwork.

    So if you dont like the high static and just lower fan speed to attain a lower static, what is your airflow now?

    I guess I look at it as ,what are the statics AFTER I have a measured airflow.
    Not what are my statics, so my airflow should be.....

    When I did some balancing a long time ago, the equipment static profile was taken after the equipment airflow was set and balanced.

    Sent from my SM-G950U using Tapatalk

  4. #17
    Join Date
    Jul 2007
    Location
    Delta BC Canada
    Posts
    136
    Post Likes
    It has to do with fan laws and energy required to move the air down the ductwork.When you increase the cfm you are trying to push more air down the same size duct and the SP will increase to the square of the original SP.Also the HP would increase by the cube .

  5. #18
    Join Date
    May 2015
    Location
    Northern Virginia
    Posts
    34
    Post Likes
    Thread Starter
    I'm past the science of static I get it.
    This is a very popular setup that I find and no one makes this adjustment on installs and most are oversized because techs are afraid to do the math and bigger is better. NOT
    So your duct work is measured and sized for 1000 cfm and your furnace is dialed in at 1350 and has been for lets say 5 years. The customer says they are uncomfortable in their second floor bedrooms. I check the static and it's 1.04 I make the adjustment to medium/high and get the static to .98. A week later they tell me their rooms are cooler and their humidity is down 2%. Do we call it success? I have not done a hot wire test yet for cfm for this unit.
    I find 1 in 20 don't have test holes for TESP

  6. #19
    Join Date
    Aug 2002
    Location
    Southold, NY
    Posts
    22,113
    Post Likes
    Quote Originally Posted by LRB View Post
    I'm past the science of static I get it.
    This is a very popular setup that I find and no one makes this adjustment on installs and most are oversized because techs are afraid to do the math and bigger is better. NOT
    So your duct work is measured and sized for 1000 cfm and your furnace is dialed in at 1350 and has been for lets say 5 years. The customer says they are uncomfortable in their second floor bedrooms. I check the static and it's 1.04 I make the adjustment to medium/high and get the static to .98. A week later they tell me their rooms are cooler and their humidity is down 2%. Do we call it success? I have not done a hot wire test yet for cfm for this unit.
    I find 1 in 20 don't have test holes for TESP
    70 - 80 % of the calls I get are the same, Oversized equipment on Undersized ducts

    Welcome to the Wonderful World of HACK sizing & installs!

  7. Likes vin lashon liked this post
  8. #20
    Join Date
    Feb 2016
    Location
    Louisburg Kansas
    Posts
    3,152
    Post Likes
    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.
    No man can be both ignorant and free.
    Thomas Jefferson

  9. Likes icy78 liked this post
  10. #21
    Join Date
    May 2006
    Location
    Philadelphia, PA
    Posts
    2,058
    Post Likes
    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.
    Climate Control Solutions for your Home or Office

    Serving Northeast Philadelphia and Surrounding Areas

  11. #22
    Join Date
    May 2015
    Location
    Northern Virginia
    Posts
    34
    Post Likes
    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?

  12. #23
    Join Date
    Feb 2016
    Location
    Louisburg Kansas
    Posts
    3,152
    Post Likes
    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

  13. #24
    Join Date
    Sep 2002
    Location
    Virginia
    Posts
    5,820
    Post Likes
    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

  14. #25
    Join Date
    Mar 2018
    Location
    Maryland
    Posts
    205
    Post Likes
    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.

  15. #26
    Join Date
    Aug 2009
    Location
    Beatrice, NE
    Posts
    8,743
    Post Likes
    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.

Page 2 of 3 FirstFirst 123 LastLast

Posting Permissions

  • You may not post new threads
  • You may not post replies
  • You may not post attachments
  • You may not edit your posts
  •