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Hazen-Williams equation

Radman
Radman Member Posts: 78
in Radiant Heating
Hi Wallies,

How do I apply the Hazen Williams equation to determine GPM through a system if I can read the pressure drop in PSI across the pump?

Anyone have experience with this to determine actual GPM?

Any help would be hot.

Thx!

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Comments

  • Mark Eatherton
    Mark Eatherton Member Posts: 5,858
    edited November 2009
    The easy way....

    If you have the pressure differential across the pump, then you convert PSI to feet of head. There are 2.307 feet of head per 1 PSI. Once you know how many feet of head you have across the pump, you go to the manufacturers performance curve for that product, go up the Feet of Head scale until you come to the feet of head you determined the circ was generating, and move across to the intersection of the performance curve, then drop straight down to the GPM and read how many Guppies Per Minutia you are moving.HTH



    ME



    PS, check out this web site http://www.engineeringtoolbox.com/hazen-williams-water-d_797.html



    Lots of cool tools here.



    ME

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  • Radman
    Radman Member Posts: 78
    Really? That simple?

    Why didn't I think of that?

    So, basically use the pressure drop converted to ft of head and cross it on the pump curve.   I can do that.   Now if I could just get other contractors to put petes plugs in before & after their pumps.... Ah so much to fix so little time

    Now, here's the biggie... I am in the field, old multi story apartment building, no pump data or curve, and two 1/4" ports on the pump flanges...

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  • Mark Eatherton
    Mark Eatherton Member Posts: 5,858
    Been there, done that, got the scars to prove it...

    You have a few options.



    1st is to take pictures, and dimensions of the existing pump. There are only 3 or 4 manufacturers commonly used here in Colorado. B&G, Taco, Paco, and others. Get as many dimensions as you can, flange to flange, casting numbers, motor voltage, amperage etc. etc



    Post the picture here and ask people whose pump it is. Once you determine whose pump it is, then you go to the manufacturers rep and see if they can help you. The only possible wrench in the works would be an impeller that had been trimmed prior to install. You can determine that by pulling the pump out of the volute.



    The other option would be to attempt to reconstruct the original system design, which if you can actually see what's there, is relatively easy to do. Then, based on a skin loss, calculate how many GPMs you need at a 20 degree DT, calculate required head, and select a new pump for that application.



    My recommendation would be to go back in with a variable speed, constant head pump. I have some articles out at www.Contractormag.com on sizing commercial VS, CH pumps.



    Good luck bubba.



    ME

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