Emerson Liebert iCOM, Manual

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Operation
Liebert
®
iCOM
®
for Liebert DSE
™
22
Minimum Fan Speed
The Liebert DSE is designed to control fan speed down to 55%. Contact your local Emerson dealer for
more information if fan speed minimum settings must be lowered.
Additional fan speed configuration parameters include a fan speed filter and fan speed reposition
delay timer. These parameters allow fine tuning the fan speed control and, except for setting to
Manual, are applicable to any other operation mode set in the VSD fan speed setting.
• The fan speed filter allows the fan to respond at a different rate depending on the location of the
control point within the proportional band.
Example : When the controlled temperature is near the setpoint or at conditions where the
proportional band output is decreasing and approaching 0%, the fan speed change rates are
proportionally decreased to avoid overshooting the controlled temperature. However, when the
temperature rises above the setpoint or at conditions where the proportional band output is
increasing, the fan speed change rates are proportionally increased.
• The fan speed reposition delay timer setting in the Liebert iCOM menu may be changed to
improve the fan operation stability if it is oscillating. The delay timer holds back the fan output
change until each delay period is reached if fan speed is decreasing. If fan speed is increasing,
then the delay timer has no effect.
3.1.2 Back-Draft Fan Damper
The Liebert iCOM controller has the ability to operate EC fans at very low speed to effectively act as
a back-draft damper. The power used to prevent air flow from entering a standby unit from the raised
floor by spinning the fans at a low speed is much less expensive than the additional static that
conventional mechanical dampers introduce while the unit is in operation.
Mechanical Fan Dampers
• No damper = Waste of efficiency, mixture of discharge and return
• Increase pressure drop during unit operation
• Up-front cost of mechanical dampers
• Increases unit height or adds complexity under floor
EC Fan Dampers
• Fans rotate at low speed to prevent air flow through unit
• Adjustable, based on application
• No pressure drop during unit operation
• No up-front cost as with mechanical dampers
Figure 18 Energy efficiency— Air bypass through unit, no mechanical damper