Pump Pressure Differential
The pump pressure differential must to be maintained above a minimum for cooling and lubricating flow to be provided to the
pump motor and bearings. The differential is controlled by EEV position. When the system switches to EconoPhase operation,
the EEV control changes from superheat control to manual control. The Vertiv™ Liebert® iCOM™ controller then signals the
EEV to control its position based on pump differential , unless during pump mode operation, the suction superheat drops
below the minimum acceptable level, then the EEV will begin to close and restrict refrigerant mass flow to build superheat.
The pump differential setpoint is 20 psid. If the pump is running at a high speed at a steady rate, the actual pump differential
may be above 25 psid.
If the pump differential drops below 5 psid continuously for 30 minutes, the system will switch to direct expansion mode for 30
minutes. The system will switch back to Vertiv™ Liebert® EconoPhase if the conditions are still qualified for pump operation.
10.3.2 Pump Start-up Routine
When either pump attempts to start, the first attempt will be at 80% of full speed. If flow is not established (as detected by
pump differential being at least 12 psid within 60 seconds), the pump will turn Off for 10 seconds before trying again at 90%
speed. If flow is still not established, the pump will turn Off for 10 seconds before trying again at 100% speed. If flow is not
established after the 100% speed attempt, the system will switch to DX mode for 10 minutes before attempting to start the
pumps again if the conditions are still compatible.
The second start-up routine is the same as above. If the second start-up attempt is unsuccessful, the system will switch to DX
mode for 60 minutes before trying again.
The third start-up routine will be the same as above. If the third start-up attempt is unsuccessful, a Pump Startup Fail alarm
will be displayed and Vertiv™ Liebert® EconoPhase operation will be locked out until the user manually resets the event at the
Vertiv™ Liebert® iCOM™.
10.3.3 Switch from Compressor Operation to Pump Operation
The Vertiv™ Liebert® iCOM™ runs the system in the most efficient operating mode, given the load and temperature
conditions. If Mixed Mode is available, the system will change from Compressor Mode to Mixed Mode when partial Vertiv™
Liebert® MCV operation is possible and from Compressor or Mixed Mode to Pump Mode when full Liebert® MCV operation is
possible.
10.3.4 Switch from Pump Operation to Compressor Operation
The unit will switch from Pump Mode to Mixed Mode or Compressor Mode when at least one of the following is true:
• The difference between the actual controlled air temperature and the setpoint is 75% into the Cooling
Proportional Band for five minutes. The default is 75%, but the percentage can be changed at the Vertiv™
Liebert® iCOM™.
NOTE: At start-up and at switchover from compressor operation to pump operation, more time is allowed to bring the
temperature under control, but the temperature will never be allowed to go outside the cooling proportional band +
2°F (1.2°C).
• The pump differential pressure is below 5 psid for 30 minutes.
• The refrigerant temperature leaving the pump is below 30°F for 60 minutes.
• The pump does not establish flow at a pump start-up attempt.
• Power is lost at the Vertiv™ Liebert® EconoPhase unit.
10 Control Operation Proprietary and Confidential ©2024 Vertiv Group Corp. 39
Vertiv™ Liebert® MCV Installer/User Guide
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