One caution point we need to take care with parallel pumping of different pump capacities is to
ensure the operating head pressure does not cause the pump of lower capacity to operate at
shut-off conditions and cause over-heating, i.e. at point X.
Therefore, it is very important to have a thorough understanding of the operating condition when
operating parallel pumps. Always check with the pump curves.
Pumps may also operate together in series. This is done to increase the head pressure for a
particular flowrate. However, it is not recommended for the mini chiller units to be installed in
series. This will cause problems in controlling the water temperature and may cause damage to
the heat exchangers and pumps.
Should the need arises, install the pump along the water discharge line to boost the head
pressure.
Example
: The head pressure of the pump in chiller C1 is not sufficient to overcome the total
friction loss to the the load. Therefore, an additional pump P1 is installed to increase the
head pressure at the same water flowrate, Q, from HP1 to HP2.
C1 LOAD
P1
LOAD C1
The pump curve will look as follows:
Head pressure combined pump curve with the
head pressures added together for
HP2 C1 and P1
pump curve of chiller C1
HP1
pump curve of P1
Flowrate
Q
Section 5 Page 81
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