Building Services Engineering 5th Edition Handbook

Heating 101
return pipes. The frictional resistance of the pipe fittings amounts to 25% of the measured
pipe length. Flow and return water temperatures at the boiler are to be 85 ◦ C and 72 ◦ C
respectively. Each radiator is situated in a room air temperature of 20 ◦ C. The heat outputs
of radiators 1, 2 and 3 are 1, 2 and 3 kW respectively. Pump C of Fig. 4.20 is to be used.
Find the pipe sizes for the system.
For radiator 1:
q 1 =
1.1 × 1
= 0.02 kg/s
4.19 × (85 − 72)
Similarly, for radiators 2 and 3:
q 2 = 0.04 kg/s
q 3 = 0.06 kg/s
Water flow in the distribution pipework will be:
q X = 0.12 kg/s
q Y = 0.10 kg/s
Water flow rate through the pump is:
q X = 0.12 kg/s
Available pump head, from Fig. 4.19, is:
H = 6m
Pump pressure rise is:
p = 9807 × 6 N/m 2
= 58 842 N/m 2
The index circuit is from the boiler to radiator 3; thus the measured pipe length is:
2(10 + 3 + 10 + 3 + 10) m = 72 m
Therefore,
EL = 1.25 × 72 m
= 90 m