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Thread: Non standard air Velocity pressure to CFM

  1. #1
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    Non standard air Velocity pressure to CFM

    Had to do a lot of equations today (actually still working on them) for a customer so they could fill out EPA permits.

    None of my instruments auto correct for flue gas temperature or density.

    So I had to not only do 20 point traverse of 3 stacks in multiple fire rates, I also had to figure out the air density for those various temperatures.

    And that was the easy part

    Now Im sitting and doing a FPM calculation for each traverse point so I can find an average FPM to calculate the flow rate.

    This is fairly tedious. Not that big a deal, cause I very rarely have to do all this.

    Its got me thinking.

    Is this process what the old timers had to do for every duct that needed a traverse in a building?

    That would be a daunting amount of paperwork.


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  2. #2
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    Sounds like a job for... A spreadsheet

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  3. #3
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    Quote Originally Posted by shellkamp View Post
    Sounds like a job for... A spreadsheet

    Sent from my Moto Z (2) using Tapatalk
    I set up the equation in a formula creator app, so its doing the math for me.

    I did have to do a couple by hand to make sure I loaded the calculation correct in the formula app, since there is no square root function. So it was some trial and error to find the right syntax to use to make the program understand.

    Spread sheet would probably work nicely though. But Id have to figure out that program too.


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  4. #4
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    Quote Originally Posted by heatingman View Post
    I set up the equation in a formula creator app, so its doing the math for me.

    I did have to do a couple by hand to make sure I loaded the calculation correct in the formula app, since there is no square root function. So it was some trial and error to find the right syntax to use to make the program understand.

    Spread sheet would probably work nicely though. But Id have to figure out that program too.


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    How soon do you need this done? Send me the info and the formulas you're using and I bet I can come up with something in excel

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  6. #5
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    I appreciate the offer.

    But after I thought about it after you first mentioned it, I started messing with the Excel program, and figured it out again. Been a while (years, 10 maybe) since I used it regularly.


    Its not pretty, but functional.

    Maybe I will learn how to pretty it up.

    And its way faster, so thanks for the suggestion.


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  8. #6
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    Yep, that's what we used to do. Quickest way was to use two techs.

    One on the ladder running the pitot tube, the other recording the Vp readings he was calling out, and when the readings were recorded, one guy would call out the Vp while the other used his calculator to find FPM, and in the end one, would call out the FPM numbers while the other would run the calculator for average, then finish the calculation. Sounds more complicated than it really is, and it actually goes pretty quickly.

    Nowadays, the machines do a lot of the calculating for you, and that's great.

    That's an example where newer is better, but when it comes to flow hoods, nothing beats an old analog flow hood. Depending on the job, sometimes a digital hood can be a worthless aggravating POS.

  9. #7
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    Yep, that’s what I used for physics class for lab experiments. Been a while since I had to write in Excel though. It would plot graphs and all.
    "The only true wisdom is in knowing you know nothing" Socrates

  10. #8
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    Do any of you use Mathcad?
    No man can be both ignorant and free.
    Thomas Jefferson

  11. #9
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    Never


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  12. #10
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    It was a lot of work. However most people just guessed a lot. A lot of companies provided you nifty slide rules that helped a lot too.
    We still did a better job in those days with paper and pencil that they guys with computers do today.
    Main reason is that in those days most engineers became engineers AFTER they spent time in the trade. Many engineers these days cant turn a screwdriver.

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