Plumbing Systems
Example Solution
1. A small office building has two plumbing clusters
(see figure 1) with a total of 8 flushometer siphonic
valve toilets, 8 lavatories, 2 service sinks, and 2
drinking fountains, using “public” numbers,
determine...
► Total
fixture units:
WC 8@10 = 80.0
LAV 8@2 = 16.0
SS 2@3 = 6.0
DF [email protected] = 0.5
102.5 wsfu
(MEEB 11th) T.21.15, p.991
(MEEB 10th) T.21.15, p.974
1. A small office building has two plumbing clusters
(see figure 1) with a total of 8 flushometer siphonic
valve toilets, 8 lavatories, 2 service sinks, and 2
drinking fountains, using “public” numbers,
determine...
► Total
Demand flow (gpm):
Use curve 1...68 gpm
(MEEB 11th) T.21.65a,
p.992
(MEEB 10th) T.21.65a,
p.975
The street main pressure is 42 psi. The most critical fixture (a
water closet) is 10’ above the inlet main. The developed
length is 80’. What diameter building main would you select
(presuming an equal friction loss is maintained in all pipe
sections)?
► Flow
pressure 15psi
(MEEB 11th) T.21.14, p.987
(MEEB 10th) T.21.14, p.970
► Static
► TEL
Pressure head 10/2.3 = 4.3 psi
= 80*1.5 = 120’
Two approaches:
1. equivalent length
or
2. multiply DL x 1.5
TEL= DL x 1.5
Proper fixture flow pressure
+ Pressure lost due to height
+ Pressure lost due to friction
+ Pressure lost through meter
Total street main pressure E
or
C=E-A-B-D
A
B
C
D
► Meter
@1-1/2” diam = 10.0 psi
► 42-15-4.3-10=12.7*100/120=10.6 psi/100’
55 gpm <68 gpm X
(MEEB 11th) F.21.63a, p.988/F.21.64a, p.989
(MEEB 10th) F.21.63a, p.971/F21.64a, p.972
► Meter
@2” diam = 4.0 psi
► 42-15-4.3-4=18.7*100/120=15.6 psi/100’
160 gpm >68 gpm ok
Use 2” diameter pipe
(MEEB 11th) F.21.63a, p.988/F.21.64a, p.989
(MEEB 10th) F.21.63a, p.971/F21.64a, p.972
How many fixture units are used for
the domestic hot water?
► LAV
8x1.5 = 12
► SS 2x2.25 =4.5
16.5 WSFU
(MEEB 11th) T.21.15, p.991
(MEEB 10th) T.21.15, p.974
What demand flow rate does this
equal?
► Use
curve 2
16.5 units
12 gpm
(MEEB 11th) Table
21.65a, p. 992
(MEEB 10th) Table
21.65a, p .975
If the building drain slopes at ¼” per
foot, what diameter pipe should be
specified?
Drainage Fixture Unit (DFU)
WC 8@6=
LAV 8@1=
SS 2@2=
DF [email protected]=
TOTAL=
48
8
4
1
61
(MEEB 11th) T.22.2, p.1017
(MEEB 10th) T.22.2, p.998
► 61
DFU
Use a 4” pipe
(MEEB 11th) T.22.5, p.1020
(MEEB 10th) T.22.3, p.999
2. Size the cold
water supply
piping using the
given data from
problem 1.