Further to what Roland says, any difference between H-W and D-W friction
loss calculations are completely overshadowed by the error introduced by
arbitrarily assigned C-factor/roughness coefficient. As I have said many
times, don't waste time measuring with a micrometer when you're cutting
with a chain saw!
Joe
Roland Huggins wrote:
Although the following statement was previously made and repetition
becomes truth (like the need for roof vents in sprinklered buildings)
allow me to say, lets not repeat it anymore. It just isn't true.
Actually a head to head comparison between Hazen -Williams and Darcy-
Weisbach, HW will under estimates by a small amount that gets larger
as the velocity goes up. Now this is for black steel (it reverses
for copper). For instance a 1 in. sch 40 at 32 ft/s (86 gpm): HW -
1.46 psi/ft and DW - 1.83 psi/ft representing a 20% difference. At
10ft/s there is an 11% difference. As the pipe size increases, the
amount of difference shrinks with 2 in. showing a 15% difference.
This is not linear since 4 in. pipe shows a slightly larger
difference than a 3 in. one.
If we really want to discuss reality (verses the applied method since
sprinkler discharge does NOT reflect a science based reality), the
use of total pressure verses velocity pressure presents a very
conservative factor. Most get hung up on the second sprinkler
discharging slightly less (and miss that the second ranch line also
discharges less) but the overall system demand is greater using total
pressure.
Now if someone would show me a sprinkler that discharges all its
water in a 10 X 13 rectangle and the density is uniform, THEN I MIGHT
BE INTERESTED IN SPLITTING HAIRS
Roland
On Jan 16, 2007, at 5:50 AM, Paul Sincaglia wrote:
However, as the forum has
been kicking about for days now...Hazen-Williams overestimates friction
losses at higher pipe velocities. For our normal demand calculations
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