User manual

Operation
Liebert
®
iCOM
®
28
On single and dual digital scroll compressor systems, the first compressor is started at 25% calculated
output from the temperature proportional band and stopped at 10%. On dual digital scroll compressor
systems, the second compressor is started at 35% and stopped at 20%, see Figure 26. When a
compressor is started, the solenoid is energized longer than it is de-energized to match the call for
cooling. When the call for cooling increases to 100%, the solenoid is de-energized for the entire 15
second cycle.
Figure 26 Single and dual digital scroll compressor activation points
3.2.3 Chilled Water Control
The chilled water control valve is adjusted proportionally as the temperature control varies the
requirement for cooling from 0% to 100%. A three-point actuator or motorized ball valve is used for
chilled water cooling, as well as free-cooling hot water or heating.
The three-point actuator is driven through two digital outputs: Open and Close. The control
determines the valve position by timing how long the open or closed signals have been active based on
the valve travel time set in the Service menu / Setup submenu. To determine the initial position of the
valve, the unit must perform a 3P Reset. The 3P Reset closes the valve for a time of 110% of the 3P
Actuator run time. This calibrates the valve with the controller and ensures that it is closed. A 3P
Reset is also performed if the fan is switched Off for any reason (timer Off, unit Off, etc.). Once the
reset is performed, the three-point actuator can be configured to utilize the pre-wired feedback signal
provided from the factory. Enabling the feedback signal will eliminate the need to drive the valve
closed after a loss of power or Unit Off command, decreasing the unit’s restart time.
Valve feedback is available only on Liebert CW models; feedback is not compatible on units with fluid
economizer.
Authorized Emerson personnel should use the following steps to enable the feedback signal:
1. Turn unit Off at the display.
2. Shut Off input power at the main disconnect.
3. The feedback on the control valve uses Analog Input 1.
4. Nothing can be connected to Analog Input 1 P11 pins 1 through 4.
5. Control board DIP switch SW2 Switch 1 must be ON, Switch 2 must be OFF.
Temp Setpoint: 70°F
Proportional Band: 8°F
Deadband: 2°F
½ Dead-
band
Increasing Temperature
Comp 1
Off
½ Proportional Band
757473727170
0%
Cooling
+ 100 %
Cooling
Comp 2
Off
Comp 1 On Partially
Loaded
Comp 2 On Partially
Loaded
Comp 1 & 2 On
Fully Loaded