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Help with the order of operation of this slab heat loss equation

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toeknee
toeknee Member Posts: 20
in THE MAIN WALL
Hey all, I have here an equation for heat loss but I can't seem to figure out the order of operation for it to get the same end result the writer did when plugging in the numbers from the example he gives along with it. Also, it was printed in the book twice but they don't match.










Anyone care to look at this and explain to me how to get the same result with the example numbers? Thanks!

Tony
Arizona

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  • mattmia2
    mattmia2 Member Posts: 9,639
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    1. the equations aren't the same
    2. you don't get the same answer they give using either equation
  • mattmia2
    mattmia2 Member Posts: 9,639
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    It is correct in the 1995 edition:





    once you fix the typo it is normal order of operations

    exponents

    multiplication/division

    addition/subtraction

    then multiply by 1 expressed as the denominator over the denominator or however you want to look at it to get rid of the denominator

  • mattmia2
    mattmia2 Member Posts: 9,639
    edited March 2021
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    looks like it should be .214 instead of .124. or there was a typo in the first edition and it got carried through the example answer in subsequent editions.
  • Zman
    Zman Member Posts: 7,569
    edited March 2021
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    I have gotten lazy and just type the formulas into Excel...
    @mattmia2 is correct, Ill have to go look at my version.
    "If you can't explain it simply, you don't understand it well enough"
    Albert Einstein
  • hot_rod
    hot_rod Member Posts: 22,139
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    Good eye, here is the correct formula. It was an editing mistake by the publisher.
    Bob "hot rod" Rohr
    trainer for Caleffi NA
    Living the hydronic dream
    mattmia2
  • toeknee
    toeknee Member Posts: 20
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    You guys are all way too good!! Thanks! Its a good thing they put example problems in the book or I would've gone on using the formula with the typo. Then I would've put it into excel like @Zman does, except my formula would be wrong the whole time
    Arizona
  • Zman
    Zman Member Posts: 7,569
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    I just checked my 2012 edition and it was incorrect like @toeknee 's.
    Good catch, I made a note in mine. I usually just use the software, but occasionally for weird ones I will build a spreadsheet based on the formulas in the book
    "If you can't explain it simply, you don't understand it well enough"
    Albert Einstein
  • Zman
    Zman Member Posts: 7,569
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    I am kind of laughing that no one even mentioned the book title...
    For those scratching their heads, It is Modern Hydronic Heating, AKA "The hydronic heating bible".
    "If you can't explain it simply, you don't understand it well enough"
    Albert Einstein
    mattmia2
  • mattmia2
    mattmia2 Member Posts: 9,639
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    Because it is the perimeter term it being off by about a factor of 2 doesn't make a lot of difference in the final result in most cases.
  • STEVEusaPA
    STEVEusaPA Member Posts: 6,506
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    LOL, I actually emailed him about this mistake and another. I heard back about the first, but not the second.
    steve
  • toeknee
    toeknee Member Posts: 20
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    @STEVEusaPA oops, I did too

    @mattmia2 yeah it doesn't seem to make any critical difference. Someone would have to have a HUUUUGE cut-up building for this to cause anything
    Arizona

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