User manual

Teamwork
79 Liebert
®
iCOM
®
Figure 65 Teamwork Mode 3—Fixed speed vs. variable speed
Cascade
When data center environments require the cooling equipment to modulate from very low loads to the
full design load, iCOM can coordinate unit capacity and unit activation in accordance with the
Teamwork Mode 3 operation described above. The Liebert iCOM optimized aisle controlled units that
are placed into Standby mode will activate as the room environment demands more cooling capacity.
iCOM will monitor the rack sensors and current operating state of each unit to determine when to
activate a standby unit.
To provide the most efficient operation from a system perspective, the Liebert iCOM will first ramp
the operating units fans and chilled water valve to compensate for the increased heat load. Once the
operating units have reached a set fan speed, the supply compensation (see Figure 105) may be
activated to determine if a lower supply temperature can compensate for the load increase. Once the
supply compensation routine has reached its threshold then the Liebert iCOM will activate a standby
unit within the group.
Lead / Lag - Failure Scenarios
When redundancy configurations are required, the Liebert iCOM unit-to-unit network has built in
fail-over conditions that require no building management interaction. The first and possibly most
common failure scenario is a single unit or component failure. In this situation, the Liebert iCOM will
automatically activate a standby unit in the place of the failed unit.
Unit-to-Unit and sensor failure scenarios have also been programmed into the Liebert iCOM
controller. For example if the remote sensors fail at the unit level, the unit will continue to operate
using the other unit's remote sensor values. If all remote sensors fail, then the fan speed will begin to
operate from the supply sensor. If the supply air sensor fails, then the unit will default to 100% fan
and cooling capacity. In the event of a unit to unit network switch failure, each unit will operate from
its sensor network.
If one unit becomes disconnected from the network, the disconnected unit will run independently
according to the local sensor readings. If U2U address No. 1 becomes disconnected from the group,
each unit will run independently according to the local sensor readings.
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Variable Speed
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Area within dotted lines is
being cooled by CRAC units
controlled by Liebert iCOM
Three Units On—One Unit in Standby
Fans must operate at 100% to meet demand
3 Units x 8.1kWh = 24.3kW per hour
Four Units Operating Together
Fans can operate at 75% to meet demand
4 Units x 3.43kWh = 13.72kW per hour