Emerson Liebert iCOM Manual Download Page 41

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Operation

Liebert

iCOM

for Liebert DSE

™

3.5

Humidity Control

Several humidifier options may be installed on a particular Liebert DSE, depending on model unit

and application requirements. In some humidifier applications, operation is limited to 80°F (26°C)

return air temperature. If the return air temperature reaches the lockout threshold of 80°F (26°C) or

higher during operation, the humidifier will be disabled. After reaching the lockout threshold, the

temperature must fall to 70°F (21°C) before the humidifier becomes operational.
Contact technical support about any problems this routine may cause or for assistance adjusting the

humidifier lockout and/or reset point.
The Liebert iCOM has four humidity sensor control types: Dew Point, Relative, Compensated and

Predictive. The humidity sensor adjusts how the Temperature and Humidity Control determines the

percent requirement for humidification/dehumidification. The humidity sensor control type

parameter, Humidity Control Type, is in both the User and Service menus under Setpoints.

Dew Point

—The actual return temperature and humidity measured by Liebert iCOM is used

internally to determine the dew point. When dew point control is selected, the user will set the

humidity setpoint in degrees dew point and will also adjust the proportional band in degrees dew

point.

Relative

—The actual return air humidity sensor reading is sent to the Temperature and Humidity

Control to determine if and how much humidification/dehumidification is required. The actual return

air humidity reading is displayed on the Status menu. Unnecessary dehumidification can result when

overcooling occurs during a dehumidification cycle. This is because a higher than normal relative

humidity (RH) reading is caused by overcooling the room. This extends the dehumidification cycle.
Later, when the dehumidification ends and the return air temperature rises to the setpoint, the RH

reading falls. The final RH reading will then be lower than actually desired. If significant overcooling

occurred, the RH could be low enough to activate the humidifier.

Compensated

—The actual return air humidity sensor reading is sent to the Temperature and

Humidity Control where the Humidity Setpoint is adjusted based on how much the return room air

temperature deviates from the desired temperature setpoint. The adjusted humidity setpoint is used

for humidification percent requirement determination. For every 1°C deviation from the temperature

setpoint, the humidity setpoint is changed by 3% RH, inversely proportional: if the temperature

increases, the humidity setpoint is decreased, and vice versa. The recalculated humidity setpoint is

shown as the Actual Humidity Setpoint (User Menu, Sensor Data). As the humidity setpoint is

automatically adjusted, the high and low humidity setpoints (User Menu, Set Alarms) are adjusted

accordingly. The unadjusted humidity sensor reading is displayed on the Status menu.

Predictive

—The actual return air humidity sensor reading is adjusted before it is sent to the

Temperature and Humidity Control. The humidity sensor reading is adjusted based on how much the

return room air temperature deviates from the desired temperature setpoint. For every 1°C deviation

from the temperature setpoint, the humidity sensor reading is changed by 3% RH, directly

proportional: if the temperature increases, the humidity reading is increased and vice versa. The

adjusted humidity sensor reading is displayed on the Status menu. Units are shipped from the factory

with Predictive humidity control set as default.
If Compensated or Predictive humidity sensor control is selected, overdehumidification is avoided.

When overcooling occurs, causing an increase in the relative humidity sensor reading, the humidity

control program predicts what the RH will be when the dehumidification cycle ends and return air

temperature returns to the setpoint. This allows the dehumidification cycle to end at the proper time.
The Compensated and Predictive humidity sensor control can reduce energy consumption by

minimizing compressor and reheat operation, and eliminating unnecessary humidifier operation.

NOTE

The historical humidity sensor graphs will display the real (unadjusted) sensor readings, no

matter which Humidity Control Sensor Type is selected. The graphical sensor data is in the

User menu under Graphics.