Emerson Liebert Economizer Solutions User Manual

The Liebert iCOM control is equipped with a series of setup parameters to allow limited adjustment 

and monitoring of the Liebert Air Economizer’s dampers and sensor. To access these parameters from 

the main unit screen:
1. Press the down arrow key until User Menu is displayed.
2. From the User Menu screen, press the right arrow key to enter the Service Menu.
3. Press the Enter key once in the Service Menu and use the arrows to navigate to the ECO icon on 

the bottom row.

4. Once this icon is selected, press Enter.
The parameters for the Liebert Air Economizer are now viewable.

Parameters SA03 through SA08 of the Liebert Air Economizer screen will show the current status of 

the Liebert Air Economizer control. The Liebert Air Economizer will be activated for use if:

• All temperatures and ratios are within the outdoor sensor range
• The outdoor air is cooler than the indoor return air temperature.

Whether the Liebert Air Economizer function is available will be shown at parameter SA07—

Economizer Available.
The Liebert Air Economizer control allows the range of outdoor air acceptable for cooling to be 

narrowed by adjusting the Humidity Ratio Min and Max settings. Refer to a psychrometric chart 

before adjusting humidity ratios.

The proportional mode adjusts the output signal in direct proportion to the controller input by 

comparing the current temperature and the setpoint. The adjustable parameters to be specified are 

the setpoint (S102) and the proportional band (S104).
The larger the difference between temperature and setpoint the more the controller output will 

increase. For instance, a 10% of scale difference will change the controller output by 10%. A 

proportional controller reduces error (difference between temperature and setpoint) but does not 

eliminate it; an error between the actual and desired value will normally exist.

The additional integral mode corrects for error that may occur between the desired value (setpoint) 

and the process output automatically over time. The adjustable parameter to be specified is the 

integral time (Ti) of the controller (S105).

When a controller that possesses integral action receives an offset signal, the integral term of the 

controller will increase at a rate governed by the integral time of the controller. This will eventually 

cause the manipulated variable to reach 100% (or 0%) of its scale, i.e., its maximum or minimum 

limits. This is known as integral wind-up. 
On PI controls there are two error variables:

• the proportional error [pe]
• the manipulated error [me]

The controller output in PI control is the manipulated error.
The integral starts calculating (manipulating) as soon as there is a pe. Permanent target for the 

integral is to increase/decrease me so that after the selected integral time me is the double of the pe.
For example, at a given pe of 10% and an integral time of 1 minute me will be 11% after 6 seconds, 

12% after 12 seconds, 13% after 18 seconds, finally reaching 20% (double of pe) after 1 minute.