Humidity Control; Figure 23 Two Single-Step Compressors With Scr Reheat Set To Standard Mode; Figure 24 Humidity Proportional Band - Emerson Liebert Challenger 3000 User Manual

Figure 23 Two single-step compressors with SCR reheat set to Standard mode

Temp Setpoint : 70°F
Proportional Band : 8°F
Deadband : 0°F
66
-100%
Heating
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.
3.5

Humidity Control

The control uses the humidity proportional band to determine which operation to perform (dehumidi-
fication/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 set-
point and separates the two halves of the proportional band. Figure 24 illustrates how the humidity pro-
portional band is evenly divided on either side of the humidity setpoint, with and without a deadband.

Figure 24 Humidity proportional band

Humidification
- Hum
- 100%
humidification
Humidification
- Hum
- 100%
Humidification
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) dehumid-
ifying capacity, based on how far the humidity penetrates the dehumidification portion of the propor-
tional 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 pro-
portional band.
67 68 69
0%
½ Proportional Band
SCR On
Without Deadband
½ Proportional Band
½ Proportional Band
Cool 1
On
SCR
On
70 71 72
Cool 1 Off Cool 2
SCR Off Off
½ Proportional Band
Cooling 1 On
Cooling 2 On
Dehumidification
½ Proportional Band
0%
Setpoint
With Deadband
Dead-
band
½ Proportional Band
0% 0%
Setpoint
27
Cool 2
On
73 74
100 %
Cooling
+ 100%
Dehumidification
Dehumidification
+ 100%
Dehumidification
Operation
+ Hum
+ Hum