User manual

Operation
27
Figure 23 Two single-step compressors with SCR reheat set to Standard mode
3.5 Humidity Control
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 24 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.
NOTE
Using SCR in Standard mode in conjunction with variable cooling capacity (e.g., chilled water
valve or digital compressor) provides ultimate capacity control and energy-efficiency gains.
Temp Setpoint: 70°F
Proportional Band: 8°F
Deadband : 0°F
Cool 2
On
Cool 1
On
Cool 2
Off
Cool 1 Off
SCR Off
SCR
On
0%
100%
Cooling
-100%
Heating
7471 72 7366 67 68 69 70
½ Proportional Band
Cooling 1 On
Cooling 2 On
½ Proportional Band
SCR On
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