User Guide

Plumbing Design Assistance Manual l Chapter 4 – Pipe sizing l 41
Hazen-Williams method
The Hazen-Williams method is
another method for sizing PEX.
However, it is not preferred by
Uponor (especially for heating
and cooling system sizing). Like
the Darcy-Weisbach formula,
this formulation is also based
on empirical relationships with
water owing through pipes.
However, correlation with test
data is much more limited. This
formulation set was derived
for re sprinkler design and
large water supply networks
with 3" and larger piping. It is
also strictly for 100 percent
water and does not account for
temperature and uid viscosity.
Since its development,
additional temperature
correction and uid correction
factors have been established.
However, results can show
signicant error when
compared to test data.
The following equation shows the Hazen-Williams method.
100
1.852
q
1.852
h
ƒ
= 0.2083 •
(
–––
)
•
––––––
C D
4.8655
Where,
ft
water
h
ƒ
= head loss due to friction per 100 ft
(
––––––––––
)
100 ft
pipe
C = Hazen-Williams roughness constant
The Hazen-Williams roughness constant for Uponor PEX-a is 163.
q = volumetric ow rate (gpm)
D = internal pipe diameter (in)
Figure 4-7: Friction loss comparing Darcy-Weisbach vs. NSF test data
0
1
2
3
4
5
6
7
8
9
10
0.25 0.50 0.75 1.00 1.25 1.50 1.75 2.00 2.25 2.50 2.75 3.00
Pressure differential — ft.
Pipe size — nominal
Pressure differential
NSF test P (ft)
P (ft)
Calculated