Two conditions must be met to stage in a VFD:
1. The system has decreased to a value (PSI, GPM, FT) equal to 1.4.1 ANALOG SETPOINT 1 minus
1.5.15 STAGE ANALOG LAG. NOTE: Primary Slave VFDs and Primary Master Drives will ignore
the 1.5.2 STAGE PUMP DELAY parameter, and immediately stage in if the system pressure drops
below the threshold.
2. The time set by 1.5.2 STAGE PUMP DELAY has expired. This delay allows a momentary drop in
system pressure without calling for a drive to stage in.
Steps To Stage A Drive:
1. The selected drive will be staged in. The selected drive is based on the order given in the tables
above. This will either close the Slave VFD’s corresponding relay or move the Master VFD out from
sleep mode.
2. The speed of the master pump will decrease to a value equal to 1.1.2 MAX FREQUENCY minus
the corresponding 1.5.7 STAGE FREQUENCY REDUCTION 1.
3. The Master VFD will operate at a reduced speed for a period set by 1.5.4 STAGE TIME.
4. When 1.5.4 STAGE TIME has expired the system will resume normal constant pressure control.
Note: The Master VFD does NOT have corresponding 1.5.7 STAGE FREQUENCY REDUCTION 1
or 1.5.4 STAGE TIME parameters.
Destaging:
Drives are destaged when the drive has slowed the master pump to maintain control pressure and the Slave
VFD(s) causes a rise in pressure.
Three conditions must be met to destage a VFD:
1. The system measured value (PSI, GPM, FT) has increased to the value set by 1.4.1 ANALOG
SETPOINT 1 plus 1.5.16 DESTAGE ANALOG LAG.
2. The time set by 1.5.3 DESTAGE PUMP DELAY has expired. This delay prevents destaging VFDs
due to momentary pressure overshoot.
The Master drive frequency is between 1.1.1 MIN FREQUENCY and the value of 1.1.1 MIN FREQUENCY
plus 1.5.6 DESTAGE MIN FREQUENCY.
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