Emerson Liebert iCOM, Руководство пользователя, Страница: 81 / 172

Teamwork
73 Liebert
®
iCOM
®
for Liebert DSE
™
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 individual 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.
Application and Configuration of Rack Sensors
The inlet rack temperature sensors should be placed on a rack that is within the area of influence of
the connected cooling unit. The following floor plan shows how the sensors should be placed. The
sensors and units are color matched to show the location of each unit's sensors. This particular floor
plan shows how the sensors can be interlaced with one another to provide redundancy of the different
unit's sensors. Remember that the sensor data from each unit is shared at the teamwork level so
placement of the sensors is flexible with your specific application. So even when one unit fails the
other units are still able to react based on the failed units sensors.
Each unit can connect up to 10 sensor modules with each module allowing for two temperature probes
for a total of 20 temperature readings per cooling unit. Each of the two probes allows for 6 feet of
distance between the temperature probe and the module. This provides the flexibility to either place
both temperature sensor probes at the top of two different racks or to place one sensor probe in the
middle of the rack and one at the upper two thirds of the rack. Sensors can be placed in other
locations like the hot aisle but should be set as a reference sensor and not a controlling sensor. This
will allow the sensor to be monitored by the Liebert iCOM display and building management system
but will not affect unit operation.
The rack sensors that are set to control have the flexibility to be set in different averaging schemes.
There are three different levels of sensor calculations; at the sensor level, at the unit level and at the
system level (unit to unit network). At the sensor level, the two probes on each rack sensor can be set
to average or take the maximum value of the two sensors. The setting at the unit level allows the
operator to select how many of the controlling sensors are averaged. If the unit has 10 rack sensors
connected for control, the operator can elect to average 1 through 10 of the sensors. For example,
selecting 3 sensors to average would use the 3 highest sensor readings out of the 10 possible sensors.
Even though only three sensors are being used for the average, all 10 are being dynamically
monitored with Liebert iCOM’s rack sensor scanning routine. This means that the three highest
sensors today might not be the three highest sensors tomorrow.
The system level calculation provides the same level of flexibility as described above for the unit level
sensor configuration. Providing this level of configuration at the unit and system level coupled with
the rack sensor scanning allows the units and system to be setup for a variety of applications,
including no containment, end containment and total containment. In addition it also allows Liebert
iCOM to adjust airflow and cooling capacity as the environment changes or if the heat load shifts,
increases or decreases.