24
Pump head and flow rate are two important parameters for pump selection. Selection of water pumps in the
water system is introduced as below.
■ Selection of hot water circulating pump
Head of the hot water circulating pump H
2
should be 1.1~1.2 times of the sum of water pressure drop
of heat exchanger at the water side of the unit ΔP, hot water inlet/ outlet height difference of the tank Z
2
,
pipeline fractional head loss and local resistance loss. Fractional head loss and local resistance loss
may be calculated by two means: the one is based on hydraulic calculation (refer to contents below for
calculation method); the second is to estimate based on experience, namely, taking local resistance loss
as 5m of water column and taking fractional head loss as 5m of water column for each 100m long of
pipeline. If the pipeline length is L
2
, the experience formula should be:
H
2
≥1.1~1.2 (ΔP+Z
2
+0.05L
2
+5) Formula (11)
Flow rate of the hot water circulating pump is selected based on the circulating water flow rate.
■ Selection of hot water circulation booster pump at the user side
Head of the hot water circulation booster pump at the user side H
3
should be 1.1~1.2 times of the sum
of the height difference between the hot water outlet of the water tank and the highest point on the water
system pipeline at the user side, pipeline fractional head loss and local resistance loss. Fractional head
loss and local resistance loss may be calculated by two means: the one is based on hydraulic calculation
(refer to contents below for calculation method); the second is to estimate based on experience, namely,
taking local resistance loss as 5m of water column and taking fractional head loss as 5m of water column
for each 100m long of pipeline. Besides, outlet pressure Pe should also be guaranteed for the user’s
showering equipment (the minimum working head should usually be 5~7m). If the pipeline length is L
3
,
the experience formula should be:
H
3
≥1.1~1.2 (Z
3
+0.05L
3
+5)+P
e
Formula (12)
Note: flow rate of water pump should be 1.2 times of the "designed hourly water consumption
G
h
". It is recommended to install backup pump to ensure normal use in case of pump failure or
maintenance.
Water pump selection
