On the MeyerFire University side of things we've been getting into the fundamentals of hydraulic calculations and the basis for how we perform calculations today.
One of the concepts that I had not explored in any kind of detail was the Hazen-Williams formula itself - outside of perhaps a few hand calculations here or there when studying for a NICET or the PE Exam. It was developed early 20th center by Gardner Williams and Allen Hazen when they studied records of friction loss measurements from a range of experimenters. The formula they derived was empirical. For hydraulic calculations - it's been the staple our industry and the basis behind our systems today. I'd be particularly interested in diving a little deeper than we typically would to get a job done, and that might come in posts here in the next few weeks. How do we reduce pressure loss in our systems? What does the actual construction of the formula tell us about flow in our system? WHAT THE FORMULA SUGGESTS The exponents here are relevant - because of that 1.85 exponent - if we double our flow, then our pressure loss increases by 260%. If we triple our flow, then the pressure loss is 7.6 times the original! Exponents affect the C-Factor too. If our C-Factor improves from 100 to 120, our pressure loss drops 29%. What applications could that have for us? Well, if we install nitrogen on a new dry system - our C-Factor goes from 100 to 120. That could be a big deal on the right projects. What about diameter? With the 4.87 exponent, that has the biggest effect of all. If our diameter doubles, our pressure loss drops 97%! Even going from 2-inch to 2.5-inch drops pressure loss by about 60%! Of the variables in the Hazen-Williams equation, diameter has the greatest impact on friction loss. HYDRAULIC PARALYSIS We know that intuitively as pipe diameter is our first go-to for solving hydraulic issues and is also the one element we have the most control over as a designer. One concept not to gloss over, though, is the pipe schedule. Even seemingly minor differences in pipe schedule (thickness) can have a major effect on pressure loss considering that the effects of diameter have an exponential effect on pressure loss. If you're banging your head against a wall trying to round out a hydraulic calculation, make sure that all of your pipe diameters are optimized (of course), but also check that your pipe schedule is accurate. The difference between a Schedule 40 and Schedule 10 calculation over a long enough distance and a sensitive-enough portion of the calculation could have a big effect on pressure loss. Also - if you're ever stuck - try our tipsheet on ways to get out of a jam (Article #1 and Cheatsheet #2). In experimenting around with different values, I went ahead and put together a small calculator that does a Hazen Williams calculation with a few helpful lookup tables already included. If you don't see the tool below, click to check it out:
If you're well into your career, this might not present a whole lot of practical need - any sprinkler hydraulic calculation program already has this incorporated of course.
What I wanted to do is simply break out the calculation to explore the effects in a little more detail. Take the sample calculation, and tweak the inputs just a bit - you can do so by clicking on a dropdown, making any selection, then use the up/down arrows on your keyboard to flip through values quickly. YOUR TAKE What do you see that people often miss about the Hazen Williams formula? What, if anything, would you want to see on this tool as a means of learning about the fundamentals? I think it would be a little interesting to start a dialogue on the limits of Hazen Williams and potential range of accuracy (that is, actually explore it mathematically and possibly disprove some of the frustrating assumptions that tend to pop up regularly). What do you want to see? Water velocity? Limits? Comparison to Darcy-Weisbach? Let me know below. Hope to nerd out a little and see what we can come up with together.
David Kendrick
3/6/2024 10:39:34 am
My understanding of Hazel Williams formula is limited to flow rates less than 32 feet per second.
JT
3/6/2024 01:17:27 pm
David,
Jack G
3/6/2024 05:28:24 pm
My understanding also , according to my grandfather and father, is the equations are accurate with velocities up to 32 fps.
Mark Harris
3/6/2024 09:07:24 pm
Long time ago when IRI was still around I think their rules were max 32 fps and fm Global was 20 fps (or maybe 25). Current Tyco watermist documents allow Hazen WIlliams for up to 25 fps and Darcy-Weisbach formula. for above 25 fps.
Fritz Descovich
3/14/2024 06:16:28 am
Hi Joe. Thanks for bringing up such a relative topic once more. May I offer the following suggestions. I am coming up on my 49th anniversary in the fire sprinkler industry on the contractor side of Comments are closed.
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+ Unsubscribe anytime AUTHORJoe Meyer, PE, is a Fire Protection Engineer out of St. Louis, Missouri who writes & develops resources for Fire Protection Professionals. See bio here: About FILTERS
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