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Thread: Static Pressure Frustration

  1. #41
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    Quote Originally Posted by WAYNE3298 View Post
    I agree Ikapigian that duct problems are the elephant. What bothers me the most about duct systems is that nothing has been done for years about determining system effect factors that are not known. Because of this there are some duct configurations that pressure losses cannot be determined.
    Steve static pressures are approximate. The value of measuring and recording component pressure drops is to assist in troubleshooting future problems.

    System effect? Some installer doesn't know what that is! This is a return I stumbled across last week . . .


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    I do a triple evac with nitro to remove non condensables.

  2. #42
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    All I can say on that one BBeerme is WOW!!!
    No man can be both ignorant and free.
    Thomas Jefferson

  3. #43
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    Yeah, I didn't know whether to laugh or cry on that one. Heat pump tripping on high head. But, believe it or not, that wasn't the worst of it.


    Quote Originally Posted by WAYNE3298 View Post
    All I can say on that one BBeerme is WOW!!!
    I do a triple evac with nitro to remove non condensables.

  4. #44
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    I think the best standardized residential duct lay outs were from the 50's maybe 60's

    Ive always called them end take off systems, but not sure what the correct term is

    But basically every branch is taken off the trunk and the trunk is reduced by the depth of the take off. Every fitting was custom made. And I beleive most had a damper at the take off also, but I could be wrong about that.

    For example their was a total of 10 branch ducts at 2 x 10 each

    At the source the trunk would be 10x20

    After the first 2 x 10 take off, the trunk became 10 x 18

    Next take off of 2 x 10, then 10 x 16 trunk continued.

    And so on. Ive seen maybe 30 such systems in the suburbs of Chicago

    Sent from my SM-G930V using Tapatalk

  5. #45
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    Here is an example https://images.app.goo.gl/jbq1zZrHoD4EAuhY8

    Sent from my SM-G930V using Tapatalk

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  7. #46
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    I have seen/admired those duct systems since I started. I thought they were older than the 50’s. A lot of them I have seen were in aluminum which as I understood was from the use of steel for the war effort.

    10 years ago I did an addition on a house with that for a duct system. The unit was on the other end of the house from the addition. I wanted to reuse as much of that old system as possible but could not make it work. It ended up I had to remove it all and start with a new plenum. It is amazing work they did back then.

  8. #47
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    You could be right. Im not sure when it started, or ended. Could have been 30's to 60's

    Most Ive seen are steel, but I could see alluminum being used instead for the war effort.

    I just marvel at the amount of time it must have taken to make all the fittings.

    Figure if I was really moving, I could make 1 fitting per hour. But realistically maybe 1 every 2 hours.

    But they would have used patterns to use for speedy layout.

    Even still likely around 1 per hour.

    Times 50 or more fittings just for the branch work.

    More time in just fab work then gets spent now days for an entire system install.

    Sent from my SM-G930V using Tapatalk

  9. #48
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    Resi problems begin at the beginning when the plenum deadheads into the main duct run. Turning vanes non-existent. Extended plenum runs with takeoffs on the end.
    A common return making rooms that are shut pressurizing and not able to receive the design air flow.
    Often there is little correct in homes. Then there's equipment in attics and crawls and flex duct looking like an octopus and not sized right.
    Give me a relay with big enough contacts, and I'll run the world!

    You can be anything you want......As long as you don't suck at it.

    If a person wants to create a machine that will be more likely to fail...Make it complicated.

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  11. #49
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    Couple all you guys have pointed out with 1/2" fan static pressure and no wonder.
    No man can be both ignorant and free.
    Thomas Jefferson

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  13. #50
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    Quote Originally Posted by heatingman View Post
    You could be right. Im not sure when it started, or ended. Could have been 30's to 60's

    Most Ive seen are steel, but I could see alluminum being used instead for the war effort.

    I just marvel at the amount of time it must have taken to make all the fittings.

    Figure if I was really moving, I could make 1 fitting per hour. But realistically maybe 1 every 2 hours.

    But they would have used patterns to use for speedy layout.

    Even still likely around 1 per hour.

    Times 50 or more fittings just for the branch work.

    More time in just fab work then gets spent now days for an entire system install.

    Sent from my SM-G930V using Tapatalk
    Don't forget how exact they have to be with the measurements as that elbow generally has to turn up between 2 joist and sometimes that is less than a 14.5" space. You wouldn't want to make up a 30" length of duct then have to cut 3.25" off of it then do the same on the next piece.

  14. #51
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    Quote Originally Posted by heatingman View Post
    I think the best standardized residential duct lay outs were from the 50's maybe 60's

    Ive always called them end take off systems, but not sure what the correct term is

    But basically every branch is taken off the trunk and the trunk is reduced by the depth of the take off. Every fitting was custom made. And I beleive most had a damper at the take off also, but I could be wrong about that.

    For example their was a total of 10 branch ducts at 2 x 10 each

    At the source the trunk would be 10x20

    After the first 2 x 10 take off, the trunk became 10 x 18

    Next take off of 2 x 10, then 10 x 16 trunk continued.

    And so on. Ive seen maybe 30 such systems in the suburbs of Chicago

    Sent from my SM-G930V using Tapatalk
    graduated duct system, as i've know them. many here in the twin cities as well, post WW1 inner ring suburbs
    my boss thinks its possible to repeal the laws of physics

  15. #52
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    The three systems of duct design I'm familiar with, equal friction, static regain, velocity reduction. the last one is not that common and I don't know who uses it. Static regain is mostly used where duct costs are high and VAV's are used.
    Our apprentices are mostly taught equal friction method and is the most used except in some commercial systems. Still it's hard to convince them not to take shortcuts and use the ol' .1 or .08 what ever is the chosen one.

    I had a joint venture with a sheet metal shop where the duct work was supposed to be demoed. The ducts were so nicely made the sheet metal co. didn't want to demo them. We had to because of contamination but they were very well done. It's interesting the effect a square throat elbow has on turbulence. Or not having turning vanes or what the different types have. Combine that with the number of fittings and it's easier to see the affects of good design can make.
    Measuring statics is a good way to see improvements being made in systems.
    Give me a relay with big enough contacts, and I'll run the world!

    You can be anything you want......As long as you don't suck at it.

    If a person wants to create a machine that will be more likely to fail...Make it complicated.

    USAF 98 Bomb Wing 1960-66 SMW Lu49

  16. #53
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    Quote Originally Posted by ch4man View Post
    graduated duct system, as i've know them. many here in the twin cities as well, post WW1 inner ring suburbs
    ran into one just today, sheet metal, although aluminum are just as common. this house was built in 1947
    my boss thinks its possible to repeal the laws of physics

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  18. #54
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    i have seen plenty of new guys really compact the flex through the penetrations, seen a return also 1/2 its size because of the cut they made.....seen the wyes installed backwards and 6 going into 8??????...im glad i got out of the residential portion of flex install because i was always correcting the screw ups...the pay at the time was not worth it ...i cannot stand using ductboard either, just non stop itching from it...ill do metal duct all day and custom shape it, making transitions on the fly sawzall in hand, 12 and 18 bender bar for the slip and drive, fast and easy..

    i dont see many 6" runs unless it went to a bathroom, 8" was the norm with all the manual dampers at the SA collars..but i followed what i was told, the logic was the flex bends reduces the airflow and creates turbulence so the true 100 cfm volume of 6"was there ...a 12" would be used instead of a 10", etc...

    getting back to rtus and splits and my experience in commercial systems that i have been doing full time for the last 9 years is a complete lack of maintenance...

    blower wheels caked with dirt and debris(what air flow? lol), adjustable pulleys at max settings, evaps badly clogged, economizers not functional or set correctly, bad economizer modules/motors, low pressure switches disconnected and criss crossed with the other circuits, low temp head pressure/cfm switches disconnected..collapsed flex duct/ RA insulation folded over causing a blockage...and my personal favorite? closed fire dampers both spring and motorized,,,,,,,.its a nightmare at times but i enjoy it better....

    i dont think i can tell you how many other guys with supposedly a ton of experience..write up a bad cfm and the ice cube relay is shot or a fuse popped due to a power surge/lightening strike ...2nd to that is a bad stat calling for heat and cool at the same time but they say its a bad control board...agghhhhh! lol

    with a show of hands...how many have seen a lennox rtu, snap a belt, get stuck in the adjustable pulley and rip out all the cfm wiring with the outdoor sensor (found all that wiring around the pulley and motor) because they bypassed the blower airflow switch safety?

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