Emerson Liebert iCOM Manual De Usuario

Delta T (Temperature Difference) Between Room and Fluid
The comparator circuit determines if the glycol / chilled water temperature of the second cooling 

source is low enough to provide at least partial cooling capacity. Free-Cooling Fluid Temperature is 

controlled in the User - Sensor Data menu, Figure 93. The comparator circuit has four settings 

(DT Between Room / FC Type, [Service Menu, Setpoints]):

• Disabled
• Contact
• Value
• Set

The Disabled setting is for standard compressorized and chilled water units that do not have a second 

cooling source. The Disabled setting can also be used to disable the second source of cooling.
The Contact setting is used when an external input is being used to determine when the second 

cooling source is to be activated. The external control communicates to the Liebert unit via contact 

closure.

• Closed = activate second cooling source control
• Open = deactivate second cooling source control

The Temp setting is the factory default (12°F [-11.1°C]) on free-cooling and dual cooling units. If the 

temperature difference between the second source cooling fluid parameter, Free-cooling Fluid 

Temperature (User Menu, Sensor Data) and room air is equal to or greater than the adjustable DT 

Between Room / FC Fluid (Service Menu, Setpoints) value, then the second source cooling fluid will be 

used to provide at least partial cooling.
The Set option allows free-cooling whenever the fluid temperature sensed (User Menu > Sensor Data) 

is colder than the temperature setpoint. The difference required between the temperature setpoint 

and the fluid temperature is adjusted on the following line DT2 Room / FC Fluid value (Service Menu, 

Setpoints). The second source cooling fluid will be used to provide cooling if the temperature 

difference between the second source cooling fluid parameter, Free-cooling Fluid Temperature and 

room air is equal to or greater than the adjustable DT Between Room / FC Fluid value.
Sensors used for this delta T are: room/local sensor or the return air sensor; and the glycol sensor.
If this delta T is true, the Free-cooling Status indication will show “On” instead of “Off”. The status is 

found in the User- Sensor Data menu, Figure 93. The primary and secondary source of cooling will 

stage accordingly. See the next sections for more information.