Appendix O — Sizing of Cold Water Supply and Distribution Piping
Gazette pages 4980–4996 · Official gazette pages (PDF, 691 KB) — use for exact tables and figures.
The water distribution within the building may be an up0feed or down0feed system. The design principles are the same for both the systems. The principal difference in the calculation procedure is that in the up feed system the difference in elevation between the fixtures and the water supply main exerts the pressure that supplies water into the fixtures, but in the down-feed system the difference in elevation between the fixtures and the roof storage tank provides the pressure to overcome the pipe friction. The following are the recommended pipe sizing procedures: O.1 The sketch of the main lines, risers and branches serving different fixtures will have to be drawn. O.2 Determine the number and types of fixture that will be required on the basis of the Table 8.6.1 in Chapter 6. O.3 The demand weight of different fixture units may be computed in terms of water supply fixture unit (wsfu) in accordance with Table 8.O.1. O.4 The peak demand load (or maximum probable flow) in liter per minute may be estimated with the data obtained in Sec O.3 using Figure 8.O.1 or on the basis of the number of occupants according to their occupancy classification specified in Table 8.5.1. O.5 The equivalent length of the main lines, risers and branches will be determined. The equivalent length of different fittings may be estimated on the basis of the data presented in the Tables 8.O.2(a), 8.O.2(b) and 8.O.2(c) or from manufacturer's specification. The total equivalent length is the sum of the equivalent lengths of all pipes and fittings. O.6 The pressure loss through water meter may be determined on the basis of their operating characteristics as shown in Figure 8.O.6 (Disk type water meter). The data for other types of water meter may be obtained from the manufacturer. O.7 The minimum pressure required at different fixtures to produce adequate flow may be estimated on the basis of the type of fixtures or minimum size of supply pipe in accordance with Table 8.5.6. O.8 The average pressure drop in kPa per meter of equivalent pipe length may be computed as follows:
F p ( P 9 . 807 H f ) / L 8.O.1)
Where, F p = Average available pressure loss (kPa) per meter of equivalent length of pipe
P = Pressure (kPa) in the water main or zero for overhead gravity storage tank.
H = Height (m) of the highest fixture above the water main or difference (m) in elevation between storage tank and the fixture under consideration.
f = Pressure loss (kPa) through water meter or such other fittings plus pressure (kPa) required to produce adequate flow through the most remote fixture in upfeed system or the fixture under consideration in down-feed system.
L = Equivalent pipe length (m) * + sign is for down-feed system and - sign is for up-feed system
O.9 The pipe size may also be estimated from Figures 8.0.5 to 8.0.10 for different
types of piping materials on the basis of the expected rate of flow determined in
Sec 0.4 and the average pressure available for friction loss ( ) in Sec O.8.
O.10 Alternative simple procedure of pipe size computation has also been explained
in the Sec 5.10.3.
Table 8.O.1: Water Supply Fixture Unit (wsfu) Values for Various Plumbing Fixtures
Fixture or group Supply Control wsfu
Cold Hot Total
Bath group Flush tank 4.5 3 6
Bath group Flush valve 6 3 8
Bathtub Faucet 1.5 1.5 2
Bidet Faucet 1.5 1.5 2
Combination Faucet 2 2 3
Kitchen sink Faucet 1.5 1.5 2
Laundry tray Faucet 2 2 3
Laundry Faucet 1.5 1.5 2
Pedestal urinal Flush valve 10 - 10
Restaurant sink Faucet 3 3 4
Service sink Faucet 1.5 1.5 2
Shower head Mixing Valve 3 3 4
Stall or wall urinal Flush tank 3 - 3
Stall or wall urinal Flush valve 5 - 5
Water closet Flush tank 5 - 5
Water closet Flush valve 10 - 10
* Fixture with both cold and hot water supplies, the weight for maximum separate
demands may be considered 75% of total wsfu.
Table 8.O.2(a): Fitting Losses In Equivalent Metre of Pipe - Screwed, Welded, Flanged, Flared and Brazed Connections
Nominal Smooth Bend Elbows Pipe 90o 90o Long 90o 45o 45o 180o or Tube Std* Rad.** Street* Std* Street* Std* Size (mm) 10 0.43 0.27 0.70 0.21 0.34 0.70 13 0.49 0.31 0.76 0.24 0.40 0.76 19 0.61 0.43 0.98 0.27 0.49 0.98 25 0.79 0.52 1.25 0.40 0.64 1.25 32 1.01 0.70 1.71 0.52 0.92 1.71 38 1.22 0.79 1.92 0.64 1.04 1.92 50 1.53 1.01 2.50 0.79 1.37 2.50 63 1.83 1.25 3.05 0.98 1.59 3.05 75 2.29 1.53 3.66 1.22 1.95 3.66 88 2.75 1.80 4.58 1.43 2.23 4.58 100 3.05 2.04 5.19 1.59 2.59 5.19 125 3.97 2.50 6.41 1.98 3.36 6.41 150 4.88 3.05 7.63 2.41 3.97 7.63 200 6.10 3.97 - 3.05 - 10.07 250 7.63 4.88 - 3.97 - 12.81 300 9.15 5.80 - 4.88 - 15.25 350 10.37 7.02 - 5.49 - 16.78 400 11.59 7.93 - 6.10 - 18.91 450 12.81 8.85 - 7.02 - 21.35 500 15.25 10.07 - 7.93 - 24.71 600 18.30 12.20 - 9.15 - 28.67 * = R/D approximately equal to 1, ** = R/D approximately equal to 1.5
Table 8.O.2(b): Fitting Losses in Equivalent Metre of Pipe - Screwed, Welded,
Flanged, Flared and Brazed Connections
Nominal Smooth Bend Tees Metre Elbows
Pipe Flow Thru Straight-Thru Flow 90o EII 60o EII 45o EII 30o EII
or Tube
No Reduced Reduced
Size Branch
Reduction ¼ ½
(mm)
10 0.82 0.27 0.37 0.43 0.82 0.34 0.18 0.09
13 0.92 0.31 0.43 0.49 0.92 0.40 0.21 0.12
19 1.22 0.43 0.58 0.61 1.22 0.49 0.27 0.15
25 1.53 0.52 0.70 0.79 1.53 0.64 0.31 0.21
32 2.14 0.70 0.95 1.01 2.14 0.92 0.46 0.27
38 2.44 0.79 1.13 1.22 2.44 1.04 0.55 0.34
50 3.05 1.01 1.43 1.53 3.05 1.37 0.70 0.40
63 3.66 1.25 1.71 1.83 3.66 1.59 0.85 0.52
75 4.58 1.53 2.14 2.29 4.58 1.95 0.98 0.61
88 5.49 1.80 2.44 2.75 5.49 2.23 1.22 0.73
100 6.41 2.04 2.75 3.05 6.41 2.59 1.37 0.82
125 7.63 2.50 3.66 3.97 7.63 3.36 1.83 0.98
150 9.15 3.05 4.27 4.88 9.15 3.97 2.14 1.22
200 12.20 3.97 5.49 6.10 12.20 5.19 2.75 1.56
250 15.25 4.88 7.02 7.63 15.25 6.41 3.66 2.20
300 18.30 5.80 7.93 9.15 18.30 7.63 3.97 2.44
350 20.74 7.02 9.15 10.37 20.74 8.85 4.58 2.75
400 23.79 7.93 10.68 11.59 23.79 9.46 5.19 3.05
450 25.93 8.85 12.20 12.81 25.93 11.29 5.80 3.36
500 30.50 10.07 13.42 15.25 30.50 12.51 6.71 3.97
600 35.08 12.20 15.25 18.30 35.08 14.95 7.63 4.88
* = R/D approximately equal to 1, ** = R/D approximately equal to 1.5
Table 8.O.2(c): Valve Losses in Equivalent Metre of Pipe - Screwed, Welded, Flanged and Flared Connections
Nominal Globe 60o – Y 45o – Angle* Gate Swing Lift
Pipe or Y Check** Check
Tube
Size
(mm)
10 5.19 2.44 1.83 1.83 0.18 1.53
13 5.49 2.75 2.14 2.14 0.21 1.83
19 6.71 3.36 2.75 2.75 0.27 2.44 Globe Lift
25 8.85 4.58 3.66 3.66 0.31 3.05 and
32 11.59 6.10 4.58 4.58 0.46 4.27 Vertical
Lift:
38 13.12 7.32 5.49 5.49 0.55 4.88
Same as
50 16.78 9.15 7.32 7.32 0.70 6.10
Globe
63 21.05 10.68 8.85 8.85 0.85 7.63
75 25.62 13.12 10.68 10.68 0.98 9.15 Valve**
88 30.50 15.25 12.51 12.51 1.22 10.68
100 36.60 17.69 14.34 14.34 1.37 12.20
125 42.70 21.66 17.69 17.69 1.83 15.25
150 51.85 26.84 21.35 21.35 2.14 18.30
200 67.10 35.08 25.93 25.93 2.75 24.40
250 85.40 44.23 32.03 32.03 3.66 30.50
Angle
300 97.60 50.33 39.65 39.65 3.97 36.60
Lift:
350 109.8 56.43 41.18 41.18 4.58 41.18
Same as
400 125.05 64.05 54.90 54.90 5.19 45.75 Angle
450 140.3 73.20 61.00 61.00 5.80 50.33 Valve
500 158.6 83.88 71.68 71.68 6.71 61/00
600 186.05 97.60 80.83 80.83 7.63 73.20
* These loses do not apply to valves with needle point type seat, ** Losses also
apply to the in-line, ball type check valve.
Figure 8.O.1 Water supply demand for various load in water supply fixture units (Wsfu)
Figure 8.O.2(a) Direct connection of roof storage tank with public water main
Figure 8.O.2(b) System incorporating balancing roof tank and direct water main connection
Figure 8.O.2(c) System incorporating underground tank
Figure 8.O.3(a) Zoning floors (5) by intermediate tanks supplied by OH storage tank
Figure 8.O.3(b) Zoning floors (5) by intermediate tanks supplied by independent pumps
Figure 8.O.3(c) Gravity water supply system with pressure–reducing valves
Figure 8.O.3(d) Hydro-pneumatic system of water supply in a building
Figure 8.O.4 Hazen-Williams nomograph with roughness coefficient, C = 100
Figure 8.O.5 Friction loss through taps and tees
Figure 8.O.6 Loss of pressure through disc - type meter in kPa
Figure 8.O.7 Friction loss in fairly rough pipe
Figure 8.O.8 Friction loss in rough pipe
Figure 8.O.9 Friction loss in fairly smooth pipe
Figure 8.O.10 Friction loss in copper pipe
Source: Bangladesh National Building Code 2020, S.R.O. No. 55-Law/2020, Bangladesh Gazette (Extraordinary), 11 February 2021. Tables, figures and equations: refer to the linked gazette pages.