Building Services Engineering 5th Edition Handbook

188 Hot- and cold-water supplies
0.5
0.4
Water flow rate (I/s)
0.3
0.2
0.1
0
0 20 40 60 80 100
Demand units
6.6 Simultaneous flow data for water draw-off points.
Table 6.3 Flow of water in copper tube of various diameters.
Δp/EL (N/m 3 )
Water flow rate q (kg/s)
15mm 22mm 28mm 35mm 42mm
1000
1500
2000
2500
3000
v = 1.5
v = 2
0.160
0.201
0.236
0.268
0.296
0.429
0.537
0.630
0.712
0.787
0.933
1.170
1.370
1.540
1.710
1.60
2.00
2.34
2.65
2.92
2.58
3.22
3.77
4.26
4.70
v = 3
v = 4
Note: v = water velocity (m/s).
Source: Reproduced from CIBSE Guide (CIBSE, 1986) by permission of the
Chartered Institution of Building Services Engineers.
3. Sum all the DU along the pipework to the water source, which will be the storage tank or
incoming water main.
4. Convert DU to water flow rates using Fig. 6.6.
5. Find the head of water H (in metres) causing the flow to each floor level.
6. Estimate the equivalent length (EL) of the pipe run to each floor in metres. This can be taken
as the measured length plus 30% for the frictional resistance of bends, tees and the tap.
7. Find the index circuit. This is the circuit with the lowest ratio of H to EL.
8. Choose pipe sizes from Table 6.3 for the index circuit.
9. Determine the other pipe sizes from the H/EL figure appropriate to each branch of the index
circuit.
10. Determine the water flow rate and head for a bronze-body hot-water service secondary
pump, if one is required.
A notation system can be adopted to gather pipe-sizing data together on drawings, as shown
in Fig. 6.7.