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iCOM
Controls Training and Service Manual
Relative Humidity Control
Relative humidity control is based on the humidity content in the return air. The
iCOM microprocessor control determines the unit humidification/ dehumidification
operation by comparing the return air humidity value to the control band that is
determined by the:
• Programmed humidity set point in %RH
• Programmed humidity proportional band in %RH
Operations and Charts
The humidity proportional control band value is divided into two parts: the humidity
set point plus ½ of the programmed humidity proportional band for
dehumidification operation and the humidity set point minus ½ of the programmed
humidity proportional band for humidification operation.
A humidity dead band can also be programmed into the control to shift the
humidification and/ or dehumidification on/ off operations away from the humidity
set point.
This programmed humidity dead band value is divided into two parts: the humidity
set point plus ½ of the dead band – no dehumidification operation and the humidity
set point minus ½ of the band – no humidification operation.
The humidity set point range is adjustable from 1 – 80% RH in increments of 1%
RH. The humidity proportional band range is adjustable from 1 – 20% RH in
increments of 1% RH. The humidity dead band range is adjustable from
0 – 50% RH in increments of 1% RH.
Humidifier Operation
The Relative Humidity control program is used to illustrate the humidification
operation in the following examples. The basic humidification control band is
established at the humidity set point with the length equal to ½ of the programmed
humidity proportional band value. The Liebert DS units are supplied with an
infrared humidifier rated at the unit capacity.
The humidity controller activates the infrared humidifier when the return air
humidity level decreases to 100% of the humidity proportional band. The
humidifier makeup water solenoid valve also operates during humidification
operation based on a timing sequence.
The humidity controller deactivates the infrared humidifier and makeup water
solenoid valve when the return air humidity level increases to 50% of the humidity
proportional control band value.
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