GPS-X Technical Reference

Other Models 332
It can be seen that when the pump flow rate increases to more than the pumping capacity
of a single pump, two pumps become operational, each pumping half of the total flow
rate [Figure 11-27A]. At this point since the flow rate are decreased for each pump, the
change in the pump operating point leads to reduced pump efficiency [Figure 11-27C].
This reduced pump efficiency increases the energy consumption significantly for the
pumping system. During the model calculation, head used in the energy calculation is the
greater of the system head and pump head [Figure 11-27C]. In general, the pump head
should always be higher than the system head for proper pumping. This condition should
always be checked by the user. If the pump head is lower than the system head, an
alternative pump having more appropriate pump characteristics curve should be used. In
this particular example, constant speed is used throughout the simulation.
Variable Speed Pump
The variable speed pump is advancement over the constant speed model described above.
In this model, user can run the pump in a variable speed mode and estimate the energy
saving that may be achieved by converting a fixed speed pump to a variable speed pump
for a given system conditions.
The additional inputs required for this model are as shown in Figure 11-26.
Figure 11-26 - Setup for Variable Speed Pump
A variable to turn the variable speed pump ON and OFF is provided. User can also
specify the minimum and maximum speed of the pump.
GPS-X Technical Reference