Emerson Liebert iCOM Manual Download Page 42

Page: 42 / 172

Operation

Liebert

iCOM

for Liebert DSE

™

The default control for humidity and dehumidification is based on dew point temperature. This

prevents the humidifier from running when not required (especially when return air temperatures

exceed 75°F [24°C]). The Liebert DSE must be operated in a conditioned space within the operating

envelope ASHRAE recommends for data centers. The maximum recommended dew point is 59°F

(15°C). Operating outside this envelope can decrease equipment reliability. Refer to ASHRAE’s

publication, “Thermal Guidelines for Data Processing Environments.”
If this default control is changed, the relative humidity setpoint must be adjusted based on return air

temperature to prevent from over humidifying the space.

3.5.1 Humidity Control Types

The Liebert iCOM has two Humidity Control Types:

• Proportional
• PI

Proportional

—The control uses the humidity proportional band to determine which operation to

perform (dehumidification/humidification) and how much capacity to provide. The Humidity

Proportional Band is a user defined range that is divided into two equal parts for dehumidifying and

humidifying.
The Humidity Setpoint is located between these two equal parts. An optional Humidity Deadband

range can be defined, which is equally divided on either side of the setpoint and separates the two

halves of the proportional band. Figure 24 illustrates how the humidity proportional band is evenly

divided on either side of the humidity setpoint, with and without a deadband.

Figure 27 Humidity proportional band

When the return air humidity deviates from the setpoint, either dehumidification or humidification is

activated. If the return air humidity increases, the control calls for 0% (none) to 100% (full)

dehumidifying capacity, based on how far the humidity penetrates the dehumidification portion of the

proportional band. If the return air humidity decreases, the control calls for 0% (none) to -100% (full)

humidifying capacity based on how far the humidity penetrates the humidification portion of the

proportional band.
When the return air humidity reaches the end of the proportional band, either 100% or -100%, full

dehumidification or full humidification capacity is provided. No operation is performed when a 0%

call is calculated. The control varies the call for dehumidifying and humidifying in 1% increments as

the return air humidity moves through the proportional band halves.
The deadband range is used to widen the setpoint. When the return air humidity falls within the

deadband, the control operates the same as if the humidity equaled the setpoint exactly. This setting

helps maximize component life by preventing excessive component cycling. The Humidity

Proportional Band and Humidity Deadband parameters are in the Service menu under the Setpoints

submenu. The Humidity Setpoint parameter is in both the User menu and Service menu under

Setpoints.

Setpoint

+ 100%

Dehumidification

Dead-

band

Humidification

- Hum