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  1. #1
    Join Date
    Jun 2005
    Location
    Winston-Salem NC
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    1,133

    for lack of a better pace

    Was looking at my ductulator yesterday while waiting for my partner to finish up a call, and noticed that the friction loss scale went all the way to 10". Residential is .08, most of the commercial systems I have been involved with have been .1

    What in the world would require 10"?

  2. #2
    Join Date
    Dec 2002
    Location
    SouthEast NC ICW & Piedmont Foothills
    Posts
    7,635
    40k cfm exhaust/dust collector/MUA maybe?
    It`s better to be silent and thought the fool; than speak and remove all doubt.

  3. #3
    Join Date
    Jun 2006
    Location
    New Jersey
    Posts
    4,337
    Quote Originally Posted by stonewallred View Post
    Was looking at my ductulator yesterday while waiting for my partner to finish up a call, and noticed that the friction loss scale went all the way to 10". Residential is .08, most of the commercial systems I have been involved with have been .1

    What in the world would require 10"?
    A lot of dust collector run up around 5" or so. And most commercial comfort cooling systems run between 1-2". I know I dealt with a mist collector one time and the airflow was insane. Don't remember the static though.

  4. #4
    Join Date
    Mar 2011
    Location
    East Coast FL
    Posts
    1,058
    An easy answer would be : large air handling equipment.

    Long runs require more pressure to deliver to space.

    Variable air volume sysems will take advantage of higher pressures to reduce duct sizing in the bldg.

    VAV terminal units will reduce pressure and velocity to maintain acceptable acoustic considerations.

    ESP's of 1" to 3" is common on built up air cond systems.

  5. #5
    Join Date
    Jun 2005
    Location
    Winston-Salem NC
    Posts
    1,133
    Thanks.
    Other than VAVs, never worked with the stuff mentioned. And the VAV's were when I was one of two sheet metal mechanics supervising about 30-ish installers.

  6. #6
    Join Date
    Dec 2002
    Location
    SouthEast NC ICW & Piedmont Foothills
    Posts
    7,635
    Quote Originally Posted by stonewallred View Post
    Thanks.
    Other than VAVs, never worked with the stuff mentioned.
    you get down toward Battery Dr., look up on those roof tops, I imagine those are high static ducts
    It`s better to be silent and thought the fool; than speak and remove all doubt.

  7. #7
    Join Date
    Feb 2001
    Location
    N.E. Iowa
    Posts
    314
    We recently did a hospital job that was actually required to be tested at 7"W.C. and the leakage was not to exceed 4%.

    I would have to go back and look at the spec book, but I think it was required to run at 4"W.C. in actual operation.
    ______________________________________________

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  8. #8
    Join Date
    Jan 2008
    Location
    windy city
    Posts
    4,435
    building where i perform most of the time has 140,000 cfm a/h's driven by a 200hp r/a and a 400hp double shafted s/a vane axials. s/p at the unit is 7''
    \m/
    original member of the racoon brotherhood

  9. #9
    Join Date
    Dec 2009
    Location
    maroon lazyboy
    Posts
    1,048
    Quote Originally Posted by heavymetaldad View Post
    building where i perform most of the time has 140,000 cfm a/h's driven by a 200hp r/a and a 400hp double shafted s/a vane axials. s/p at the unit is 7''
    That's a lot of wind, friend!!! 600 HP!!!

  10. #10
    Join Date
    Jul 2008
    Location
    Southern California
    Posts
    139
    Over the years there have been several attempts to use high pressure duct systems in commercial office buildings (4" to 8"wc). The advantages were smaller duct (cheaper) and less attic space required. The ones I am familar with would use an induction box in place of a normal VAV. The branch line to the box from the main duct would be hose like the one you would find on a vacumn cleaner (3" to 4" dia) with screw clamps on each end. The disadvantages were higher fan horsepower, higher air noise and the zone temperature control didn't seem to be that great. They were not very popular.
    Effort is the 1st step towards failure.

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