113 Liebert
®
CW
™
System Design Manual
3.4 MULTI-UNIT COORDINATION
Liebert iCOM
®
teamwork shall save energy by preventing multiple units in an area from operating in
opposing modes. Teamwork shall allow the control to optimize a group of connected cooling units
equipped with Liebert iCOM using the U2U (Unit-to-Unit) network. There shall be three modes of teamwork
operation:
• Teamwork Mode 1 (Parallel): Is best in small rooms with balanced heat loads. The controlling
temperature and humidity sensor readings of all units in operation (fan On) are collected to be used for
an average or worst case sensor reading (user selectable). The master unit shall send the operating
requirements to all operating units in the group. The control band (temperature, fan and humidity) is
divided and shared among the units in the group. Each unit will receive instructions on how to operate
from the Master unit based on how far the system deviates from the setpoints. Evaporator fans and
cooling capacity are ramped in parallel.
• Teamwork Mode 2 (Independent): Is best applied in large rooms with unbalanced heat loads. The
Liebert iCOM calculates the worse-case demand for heating, cooling humidification and
dehumidification. Based on the greatest demand within the group, each unit operates independently,
meaning that the unit may respond to the thermal load and humidity conditions based on the unit's
controlling sensors. All sensor readings are shared.
• Teamwork Mode 3 (Optimized Aisle): May be employed in large and small rooms with varying heat
loads. Optimized Aisle is the most efficient teamwork mode that allows the unit to match cooling
capacity with heat load. In the Optimized Aisle mode, the fans operate in parallel. Fans can be
controlled exclusively by remote temperature or using static pressure with a secondary remote
temperature sensor(s) as an override to ensure the inlet rack temperature is being met. Cooling
(Chilled Water Valve or Economizer) is controlled through unit supply air conditions. The Liebert iCOM
calculates the average or worst-case sensor reading (user-selectable) for heating, cooling
humidification and dehumidification. Based on the demand within the group, units will be allowed to
operate within that mode until room conditions are satisfied. This is the best form of control for a room
with an unbalanced load.
3.5 STANDBY LEAD-LAG
The Liebert iCOM shall allow planned rotation to keep equal run time on units and provide automated
emergency rotation of operating and standby units.
3.6 STANDBY UNIT CASCADING
The Liebert iCOM cascade option shall allow the units to turn On and Off based on heat load when utilizing
Teamwork Mode 1, Independent mode or Teamwork Mode 3, Optimized Aisle mode with remote
temperature sensors. In Teamwork Mode 1, Cascade mode will stage units On based on the temperature
and humidity readings and their deviation from setpoint. In Teamwork 3 Mode, Cascade mode dynamically
coordinates the fan speed to save energy and to meet the cooling demands. For instance, with a Liebert
iCOM group of six units and only 50% of the heat load, the Liebert iCOM shall operate only four units at
80% fan speed and leave the other two units in standby. As the heat load increases, the Liebert iCOM shall
automatically respond to the new load and bring on another unit, increasing the units in operation to five.
As the heat load shifts up or down, the control shall meet the need by cascading units On or putting them
into standby.
3.7 VIRTUAL MASTER
As part of the robust architecture of the Liebert iCOM control, it shall allow for a virtual master that
coordinates operation. The Virtual Master function provides smooth control operation if the group’s
communication is compromised. When the lead unit, which is in charge of component staging in teamwork,
unit staging and standby rotation, becomes disconnected from the network, the Liebert iCOM automatically
assigns a virtual master. The virtual master assumes the same responsibilities as the master until
communication is restored.
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