Emerson Liebert DS Precision Cooling System 28-105kW Manuel D’Utilisation

When the Liebert Air Economizer is being used for cooling, both the outside air damper and the room 

return air damper are active in an opposing relationship. The cooling requirement and temperature of 

the outdoor air will determine the position of the outside air damper. It will range from fully closed to 

fully open. As the outside air damper moves toward fully open, the return air damper will close to a 

minimum of 15%. The 15% minimum is to make sure that air remains circulating near the return air 

sensor. If the return air sensor is moved to another position where there is constant circulation of air 

in both outdoor and indoor modes, then the minimum 15% indoor damper position can be removed.

Risk of improper operation. Can cause degraded cooling and ventilation operation because of 

improper building air pressure.
The incoming air from the outside damper requires expelling an equal volume of air through a 

field-provided powered relief air vent (see Figure 1). The volume that must be expelled will 

vary from 0 to 80% of the total airflow for all Liebert Air Economizer units. The powered relief 

system should be sized for 80% of the total airflow for all Liebert Air Economizer units in the 

conditioned space and to maintain minimal building air pressure.

Controller settings will vary depending on the application. The objective of all settings is the same: to 

expel warm air from the conditioned space and bring in cooler air through the Liebert Air 

Economizer. This function is monitored continuously by the Liebert iCOM that controls the Liebert 

Air Economizer.
Figure 9 shows an example of the air flow pattern of a Liebert Air Economizer system. The indoor 

sensor must be positioned where there is airflow when the system is in full economizer operation and 

when the system is operating in non-economizer mode.
If the indoor damper position has been changed to 0% from the factory default of 15%, then the indoor 

sensor must be moved, preferably to the hot aisle.