Emerson Liebert iCOM User Manual download pdf (Page 29)

Operation

19 Liebert

iCOM

Minimum Fan Speed

Depending on the product control design, there may be an internal minimum speed, as defined by

that specific product operation. Minimum fan speeds are defined below.

•Liebert DS

™

units with pressure transducers 70%

•Liebert CW

™

units 60 -100% (available option to 25%)

• Liebert Deluxe System\3

™

units with low-pressure switches limited to 80%

Contact your local Emerson dealer for more information if fan speed minimum settings must be

lowered from the values above.

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.

Air Economizer with Variable Fan Speed Fans

An option in Service Menus > Setpoints > FC / AirEco Ramp Up w/CFC, allows the fan to ramp with

Liebert Fluid Economizer. The default value is No, allowing the fan ramp independently of

free-cooling. When set to Yes, the control will compare the call for fan to the free-cooling request. This

will provide the most capacity from the Liebert Air Economizer and will help in holding off the

mechanical cooling (second stage). When the Liebert Air Economizer is not available, the fan will still

ramp with the first stage of cooling but the first stage will be either a chilled water valve or

compressor operation.

NOTE

• The fan speed lower and upper limit settings are set at the factory.

• The standard fan speed control will be overridden during a call for Dehumidification if the

function is enabled. When there is a call for dehumidification, the fan speed will change to

the VSD Setpoint Dehum parameter found in the Service Menu>Setpoints. This routine may

be disabled in Service Menus>Options setup line S419.

• The standard fan speed control will be overridden during a call for humidification or reheat.

During a call for humidification or reheat, the fan speed will change to a higher speed,

which is set at the factory to eliminate the possibility of condensation or damage to the unit.

NOTE

This feature is overridden in Manual fan control. Fan control must be in a decoupled mode.

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Emerson Liebert iCOM User Manual Page 29

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