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2018 IPC table E103.3(1) available pressure calculation

  • 1.  2018 IPC table E103.3(1) available pressure calculation

    Posted 13 days ago
      |   view attached

    I have a question about row B in table E103.3(1) in the 2018 IPC. I am being told that column B (highest pressure at fixture (t-604.3)) should be omitted from the calculation. If this is true, why would it be in the table? I am confused because I would consider it a pressure loss that needs to be accounted for and I always account for it. Does anyone else use this table and if so, do you omit row B?

     

    Chad Hill

    Engineering

     

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    Attachment(s)

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    SYSTEM PRESSURE.pdf   81K 1 version


  • 2.  RE: 2018 IPC table E103.3(1) available pressure calculation

    Posted 12 days ago
    Hi Chad. The UPC Appendix A has the same requirement when calculating friction loss and really should not be eliminated. What you are driving at with the friction loss calculations is finding the allowable friction loss due to pipe friction. Your system design will need to maintain a minimum residual pressure based on the most remote fixture. If the most remote fixture requires a minimum 25psi to maintain a desired flow rate at the peak demand, then you need to allow for that in your friction loss calculations. Knowing your allowable friction loss due to pipe friction, you can then select your pipe diameters and not exceed the allowable friction loss to maintain the residual pressure.
    I suppose someone could argue that you can eliminate this from your calculation as long as you follow the pressure losses in your system design to meet the requirement of each fixture and perhaps a BIM program can make these calculations for you in the design process. But if you are using a spreadsheet and then referring to pipe sizing nomographs then you do need to include it to determine your allowable friction loss per 100ft. of pipe.

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    Dan Cole
    Sr. Director of Technical Services
    IAPMO
    dan.cole@iapmo.org
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  • 3.  RE: 2018 IPC table E103.3(1) available pressure calculation

    Posted 12 days ago
    Chad, 
    Basically,  in order to size piping, we need to know four things
    1. The pressure that will be available for the water piping system. This may or may not be with a booster pump (positive column)
    2. The static pressure loss (1 psi/2.3 feet of height) (negative column)
    3. Friction loss (negative column)
    4. and pressure required at the most hydraulically demanding fixture (negative column). This is typically, say, 35 psig at the last water closet on the highest floor. 
    The last three numbers must be subtracted from the first with a sum equal to zero (they must balance like your bank statement). You can lump these last three together if you like, then subtract them from the pressure available. Mathematically that's okay. However, they are three DIFFERENT things.Static loss isn't the same type of loss as friction loss. And the required residual pressure number is likewise different in that it is a pressure differential required to operate the fixture. 

    All three of these numbers must be included in the calculations. The IPC table is a little bit confusing because the residual pressure requirement is put in the friction loss part of the chart. To be a bit less confusing (especially to newer designers), in my opinion, the residual pressure requirement number should be put in a separate row altogether - like the static loss. 

    But again, it isn't a friction loss, but it does have to be included in the "loss column". Hopefully, the table will get revised to be less confusing. 

    Hope this helps

    Ed Hale, PE

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    Ed Hale, PE
    Plumbing/Fire Protection Chief
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  • 4.  RE: 2018 IPC table E103.3(1) available pressure calculation

    Posted 12 days ago
    Chad, 
    I failed to take a close look at the table before my reply. The pressure requirement actually IS in a separate row as it should be. But as Daniel mentioned, DO include that number. 
    Thanks
    Ed

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    Ed Hale, PE
    Plumbing/Fire Protection Chief
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  • 5.  RE: 2018 IPC table E103.3(1) available pressure calculation

    Posted 11 days ago
    Chad,
    Note that the result is the excess pressure at fixture you are calculating for "on top of the minimum required pressure to operate the same fixture" through the selected critical path in your calcs.
    hope this helps

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    Falah Al-Janabi, PE
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