User manual

Operation
Liebert
®
iCOM
®
48
Standard Mode
In Standard mode, the SCR reheat operates only when the Temperature Proportional Band calls for
heating. SCR reheat output is adjusted proportionally as the Temperature Proportional Band varies
the requirement for heating from 0% to -100%. Compressors operate only when there is a call for
cooling as described in 3.2.2 - Compressor Control.
Figure 43 illustrates how SCR reheat operates when SCR Control Type is set to Standard mode.
Figure 43 Two single-step compressors with SCR reheat set to Standard mode
3.6 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 44 illustrates how the
humidity proportional band is evenly divided on either side of the humidity setpoint, with and
without a deadband.
Figure 44 Humidity 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