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Operation
27
3.6 Humidity Control
The control uses the humidity proportional band to determine which operation to perform (dehumidi-
fication/humidification) and how intensely to perform it. 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 22 illustrates how the humid-
ity proportional band is evenly divided on either side of the humidity setpoint, with and without a
deadband.
Figure 22 Humidity proportional band
When the return air humidity deviates from the setpoint, it begins to penetrate one of the propor-
tional band halves, either dehumidification or humidification. 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 Propor-
tional Band and Humidity Deadband parameters are in the Service menu under the Setpoints sub-
menu. The Humidity Setpoint parameter is in both the User menu and Service menu under
Setpoints.
0%
Setpoint
0%
+ 100%
Dehumidification
Dead-
band
Humidification
-Hum + Hum
0%
Setpoint
½ Proportional Band
Dehumidification
- 100%
Humidification
-100%
humidification
Without Deadband
With Deadband
Humidification
-Hum
+ 100%
Dehumidification
+ Hum
Dehumidification
½ Proportional Band
½ Proportional Band ½ Proportional Band