Page 3 of 5 FirstFirst 12345 LastLast
Results 27 to 39 of 61

Thread: Static location

  1. #27
    Join Date
    Jul 2016
    Posts
    91
    Post Likes
    Read through this thread 10 times and learned something new each time. Thanks Icy and Wayne!

    Sent from my SM-G900V using Tapatalk

  2. Likes icy78, GoCougs liked this post.
  3. #28
    Join Date
    May 2014
    Location
    Bay Area California
    Posts
    25,737
    Post Likes
    I said that just today to the owner where I work, about something completely different than this thread. He doesn't care where the answers come from, just so long as I keep pulling rabbits out of the hat.

    That's why I try to contribute where I can, because I get [at least] just as much in return!


    Quote Originally Posted by icy78 View Post
    Yeah I actually pondered the round fan/square duct thing a few times. That's the first fan of that style that I have actually worked on. Then when I read the install manual again, that heatingman left, I thought about it again and thought it was worth throwing out there. I'm glad you knew the answer to that.
    I have passed on to the owners what I think. You guys get anonymous credit because I said some friends in the business helped me out.

  4. Likes ch4man, icy78, heatingman, Cagey57 liked this post.
  5. #29
    Join Date
    Feb 2016
    Location
    Louisburg Kansas
    Posts
    3,869
    Post Likes
    This is my favorite forum and I hope it lasts. Hopefully it will be increasingly more popular and more used. I enjoy most of it and like BBeerme several comments that are made remind me of past experiences. TAB work is fun because of the challenge troubleshooting presents and it is satisfying to solve problems. The only thing that frustrates me is I constantly lose my internet connection and sometimes it takes me a long time to respond to a thread.

  6. #30
    Join Date
    Feb 2016
    Location
    Louisburg Kansas
    Posts
    3,869
    Post Likes
    icy78,
    I never thought to give you the full explanation of why the inlet duct needs changed. There are valid reasons and if you need this info to convince your client let me know. Otherwise no need to bore you.

  7. #31
    Join Date
    Dec 2014
    Posts
    2,952
    Post Likes
    Thread Starter
    I'm guessing because the air needs straightening before entering the fan. But I think there's more to it.
    I'm all ears Wayne. I can assure you it won't bore me. That stuff interests me. Besides, I need to convince my boss still.
    I've got their maintenance dept convinced tho!

  8. #32
    Join Date
    Feb 2016
    Location
    Louisburg Kansas
    Posts
    3,869
    Post Likes
    AMCA is the test agency for every fan I have ever seen. Installation standards are established primarily by Air Movement Corporation of America (AMCA) and they have conducted every system effect test that I am aware of. For this fan AMCA standard 210 limits the inlet duct area to 112.5% of the fan inlet area. That is with a round duct on the inlet. You not only have a square duct but the duct area is double that established by AMCA. The minimum duct area is 91.5% of the fan inlet area. The reason for limiting the duct size is to limit turbulence entering the fan.
    You have an oversized square duct which is worse than an oversized round duct. The problem even with an oversized round duct is that the sudden reduction in area increases the velocity creating a vena contracta. The vena contracta is basically a sudden reduction in the velocity profile of the incoming air stream. The airstream quickly expands because of the negative pressure generated by the fan. This causes turbulence which is the last thing you want at the fan inlet and the result is reduced fan performance. It is not possible to accurately measure the fan inlet static pressure because of the turbulence. If you have a transition at the fan inlet swirl is normally induced making the problem worse. The return duct of 26 x 26 is OK if the transition to 20" round is completed 5 feet from the fan inlet. The convergence angle of the transition at that location should not be greater than 15 degrees.
    You may need to get a copy of the AMCA manual to convince all interested parties.

  9. Likes BBeerme liked this post.
  10. #33
    Join Date
    Dec 2014
    Posts
    2,952
    Post Likes
    Thread Starter
    It's worse than that Wayne. My fan is a 16"!
    I haven't looked for a AMCA manual at our shop but I would hope we have one.

  11. #34
    Join Date
    Feb 2016
    Location
    Louisburg Kansas
    Posts
    3,869
    Post Likes
    icy78,
    The hard sell happens because most people can relate to the slow velocity in the duct but entry to an inline fan is the most critical place in the duct system. AMCA has two or three manuals that would help you convince everyone there is a problem. They are the recognized authority when it comes to fan testing and system effect.
    The inlet airstream on your fan is entering the props too much in the center at too high a velocity because the existence of the vena contracta. Good luck winning your case.

  12. Likes icy78 liked this post.
  13. #35
    Join Date
    Mar 2009
    Location
    Several Miles from Sane
    Posts
    1,790
    Post Likes
    "Professor" Wayne and all of the rest of you, Thanks many times over. This thread has explained the cause and effect for 2 or 3 problems that have been bothering me for a couple of years.

    I'm just a Controls Guy but I get involved in trying to correct mechanical problems with controls, usually with limited success. Fortunately I have 3 TAB companies that are really good and honest to a fault that I can call on for assistance.

    This forum is a great resource. Thanks Dad (fka. Lusker) !
    If sense were so common everyone would have it !
    Stupid should Hurt !
    If people took care of their cars like they do their HVAC Systems you'd see a lot more people walking
    !

  14. Likes BBeerme liked this post.
  15. #36
    Join Date
    Feb 2016
    Location
    Louisburg Kansas
    Posts
    3,869
    Post Likes
    Cagey57,
    A good and honest balance contractor is your best friend and you are his. A bad or crooked balancer is one of your biggest pains. Thanks for the compliment but being retired this forum is pure enjoyment for me. It may even help ward off senility.

  16. #37
    Join Date
    Dec 2014
    Posts
    2,952
    Post Likes
    Thread Starter
    Update. I get to pitch my case for duct change tomorrow. Ho ho!
    Wish me luck!

  17. #38
    Join Date
    Dec 2004
    Location
    Chicago area
    Posts
    8,742
    Post Likes
    Good luck


    Sent from my iPhone using Tapatalk

  18. #39
    Join Date
    Feb 2016
    Location
    Louisburg Kansas
    Posts
    3,869
    Post Likes
    Good luck but don't be too disappointed if you can't convince them. System effect is not universally understood even by a lot of engineers who are supposed to account for it in their design. The duct silencer causing the problem in the system I previously referred to wasn't removed two years and then only after all else failed. That was more obvious than your problem. Most people think that if the duct is oversized the friction loss is less and that can't cause a problem.

Page 3 of 5 FirstFirst 12345 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
  •