Emerson Liebert iCOM User Manual Page 70

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Operation
Liebert
®
iCOM
®
60
3.9.1 Operation
Inlet Rack Temperature Control
The Liebert iCOM Optimized Aisle control monitors the inlet temperature to the racks using up to 20
rack temperature sensors that are connected to a Liebert iCOM control. These inlet rack temperature
sensors are used to control the air flow (fan speed) of each unit. The air flow is increased when the
inlet rack sensors detect a temperature higher than the setpoint and will decrease air flow when the
head load decreases or changes to the application are modified (eg., Containment).
Additional Details of Rack Temperature Operation
Refer to Application and Configuration of Rack Sensors on page 81 for rack sensor setup
details.
The cooling unit’s fan speed is determined based on the amount of deviation from temperature
setpoint (Proportional) and the length of time the actual temperature has deviated from
temperature setpoint (Integral)
The fan speed control takes into account the actual temperature as it compares to the
temperature setpoint and will modify how fast the fans can change speed to avoid overshooting
the setpoint.
In addition to the speed filters, the fan speed also has programmed independent acceleration and
deceleration rates
These control tuning parameters allow the fans to speed up quickly to match rapid heat load
changes and react to containment doors being opened and closed while still providing stable
control when the application returns to steady state operation.
Temperature Compensation
Temperature compensation links between the cold aisle temperatures, cooling capacity and air flow.
Changes that could invoke temperature compensation would be the removal of floor tiles in non-cold
aisle areas, incorrect supply temperature setpoint, unit failure in another zone or heat load changes
greater than expected heat load changes in rack equipment. As a further protection, the temperature
compensation routine also ties into the cascade /standby operation when Teamwork Mode 3 is
selected.
There are three selectable compensation routines to choose from: Return, Supply or Return + Supply.
Return Compensation: This temperature compensation monitors the return air condition and
automatically adjusts the supply air setpoint if return temperatures become too cold. Return
compensation can be enabled in all fan and temperature control sensor configurations, with the
exception of fan and cooling set for return air control (Enable Return Compensation falls back to No).
With return air compensation enabled, S103 “Temperature Setpoint” remains unchanged as long as
the air temperature is above S114 “Return Compensation Setpoint.”
If the return air temperature falls below S114 “Return Compensation Setpoint,” S103 “Temperature
Setpoint” will be increased. The calculated compensation setpoint is displayed as the left hand value
(Act) of line S103 (see Figure 49). Return compensation is also indicated from the unit view as shown
in Figure 50.
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