Emerson Liebert iCOM User Manual download pdf (Page 63)

Operation

53 Liebert

iCOM

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

humidification or full dehumidification 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.

PI—If PI Control is selected, the percent humidification/heating requirement is calculated by

combining two methods, proportional and integral. The proportional term is calculated in a manner

similar to the previously described Proportional control.

The integral term (sometimes called “reset action”) is calculated by measuring how much and how

long the air humidity has been above or below the setpoint. If the actual air humidity has deviated

from setpoint, the percent requirement is slowly and continuously increased until the total is

sufficient to bring the return room air back to the setpoint. The control helps to ensure humidity

setpoint is achieved while efficiently operating the equipment.

From an idle state (compressor[s] Off, chilled water valve closed, etc.), the call for

humidification/dehumidification is based on proportional humidity deviation from setpoint. As

humidity deviates further from or closer to the setpoint, the call for humidification/dehumidification

is increased or decreased, respectively. The amount of humidification or dehumidification applied

depends on how far the actual temperature has deviated from the setpoint on the proportional (P)

band.

The integration (I) time works with the proportional band in PI Control to stage call for components

before the room humidity deviates far from the setpoint. The “I” portion does this by doubling the

current “P” deviation for every time the “I” has elapsed.

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Emerson Liebert iCOM User Manual Page 63