• Enter the total number of CDU 600 units in the networked system via Setup screen > Group Control > Number of
Units in Group (P082)
• Enter the number of run units via Setup screen > Group Control > Number of Run Units (P083)
5.3.4 Group Control—Start Sequence from Power Up
1. Power is available when the controller is active.
2. POST (power on system test) and Firmware initializes in less than 1 second—CANbus network activity and
RS485 communications with inverters will be established within the 1 second period.
3. When the controller is initialized, it looks for messages from the other CDU 600s in the Group. Messages from
CDUs are transmitted asynchronously every 100 milliseconds, so within 200 milliseconds messages will have
been exchanged and the group demand shared.
4. When the group demand is shared, the inverters will be driven to the group demand instantly via RS485 Modbus
RTU communication from the controller.
5. The inverters are programmed with a 2 seconds ramp up period (2 seconds to 100%), so if the group demand is
typically at 65% to 75%, ramp up will take 1.5 seconds. This ramp up period is designed to prevent a secondary
discharge pressure over shoot on CDU 600 (or pump) re start. It is also configurable via the F002 Acceleration
Time parameter on the inverter.
6. Total startup time in Group Control mode is 1 second +200 milliseconds + 1.5 seconds = 2.7 seconds to the
required pump speed, pressure, and flow rate.
5.3.5 Group Control—Controls
When in group control, the lead CDU 600 modulates its pump speed to maintain a differential pressure setpoint. The
differential pressure setpoint default is an average over all the individual running CDU 600 differential pressure readings. This
can be changed to the differential pressure over all CDU 600s in the group in Setup/Group Control/P094 regardless if they
are running. All CDU 600 units work in parallel and set their pump speeds to be identical with that of the lead CDU 600.
Each CDU 600 modulates its own primary (facility) fluid control valve to maintain a group wide IT supply fluid temperature
setpoint. Each CDU 600 also locally regulates temperature using the average of its individual temperature sensors.
5.3.6 Group Control—Unit Rotation and Standby Units
Unit rotation can be configured to be weekly, monthly, or never in the Setup screen under Group Control. Upon rotation, one
of the standby units is switched on and one of the duty units is switched off. For example, if units 1, 2, 3, and 4 are running and
5 and 6 are off, after rotation units 2, 3, 4, and 5 will run while 1 and 6 off.
In the event that the load exceeds the capacity of the running units and there are standby units, the standby units will not kick
in automatically. The configured number of duty units is selected based the max load. If this max load increases, then
additional load has been added and the operator should increase the configured number of duty units.
5.3.7 Group Control—Failover Offset
Failure mode enables standby CDU pumps to start in 75 ms and a 2 seconds ramp up when a XDU1350 in the group is taken
offline. This is to seamlessly maintain system differential pressure if a unit is lost without over/undershoots.
64 Proprietary and Confidential ©2025 Vertiv Group Corp.
Vertiv™ CoolChip CDU 600 Operation and Maintenance Guide
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