Emerson Liebert iCOM Manual De Usuario

Minimum Chilled Water Temperature—This feature allows the user to select a minimum chilled 

water temperature to prevent simultaneous operation of the chilled water (free-cooling) and 

compressor(s) on units factory-programmed to operate both sources simultaneously. This feature is 

enabled in Service>Setpoints, parameter Minimum CW Temp.
If the fluid temperature sensed is below the Minimum CW Temp Value, (Service Menu, Setpoints), 

and the Delta T (Temperature Difference) Between Room and Glycol (see 3.4.1 - Differential 

Temperatures / Controls (Comparator Circuit) is satisfied, the control will operate ONLY the 

chilled water for cooling. The compressor(s) is locked out. If cooling does not operate, (i.e., loss of 

chilled water flow), the control will override this setting and activate a compressor(s). When this 

happens, free-cooling will be locked out for one hour.
If the fluid temperature is above the minimum CW value, the control will operate the chilled water 

(free-cooling) and compressor(s) simultaneously if needed. If the Minimum CW Temp is disabled, the 

control may operate both sources as load requires.

GLYCOOL units may be programmed to stage cooling components in either of two ways:

• Operate free-cooling or compressor(s) to maintain temperature (factory default)
• Operate free-cooling and compressor(s) simultaneously

Caution must be taken when operating free-cooling and the compressor simultaneously on GLYCOOL 

units. Adequate flow must be provided to the unit to prevent high pressure when 100% free-cooling is 

required in addition to DX cooling. Running too cold of fluid temperature and compressor(s) 

simultaneously may cause refrigerant pressure to drop. Contact technical support at 800-543-2778 for 

more information on simultaneous operation setup.
When the unit is configured to operate free-cooling or compressors(s), free-cooling eligibility is based 

on the comparator circuit discussed in 3.4.1 - Differential Temperatures / Controls (Comparator 

Circuit). If the circuit determines free-cooling will condition the space, the valve will open and close 

as temperature deviates from the setpoint. If the comparator circuit determines that free-cooling is 

not capable of conditioning the space, control is automatically replaced by compressor(s).
During either free-cooling or compressor operation, the control uses the temperature proportional 

band to determine which operation to perform (cooling/heating) and how much capacity to provide. 

The Temperature Proportional Band is a user-defined range that is divided into two equal parts for 

cooling and heating. The Temperature Setpoint is between these two equal parts. An optional 

temperature and heating deadband range can be defined, which is equally divided on either side of 

the setpoint and separates the two halves of the proportional band.
When the unit is configured to operate free-cooling and compressor(s) simultaneously, the comparator 

circuit determines free-cooling eligibility. Free-cooling and compressor(s) are staged based on 

temperature deviation from setpoint. The cooling proportional band is divided into two parts for 

simultaneous operation, the first portion is used for free-cooling and the second for DX operation. 

Figure 32 illustrates how the cooling proportional band is broken out on a free-cooling unit with two 

step compressors.
Cooling Control Band for Simultaneous Operation = (Temperature Proportional Band/2) / 2 + 

(Temperature Deadband/2)
If the comparator circuit determines that free-cooling is ineligible for use, the compressor band will 

shift to the left.