Emerson Liebert iCOM User Manual download pdf (Page 34)

Operation

Liebert

iCOM

3.1.6 Motorized Ball Valve in Water-Cooled Units

On water/glycol-cooled units with digital scroll compressors), pressure changes during each digital

cycle during unloaded operation. This rapid pressure change would cause a conventional water

regulating valve to open and close an excessive number of times.

Excessive valve cycling is avoided on units with digital scroll compressors) by monitoring a liquid line

transducer and regulating heat exchanger fluid flow with a motorized ball valve (MBV). The control

algorithm for the motorized ball valve uses an intelligent sampling rate and adjustable pressure

threshold (S427 Ball Valve Setpoint Offset in Figure 160) to reduce the number of times the valve

opens and closes. System reliability and performance is enhanced using a brass valve, linkage and

actuator.

Each compressor has one motorized ball valve that is driven by the analog output of the Liebert iCOM

based on discharge pressure. If there is a call for cooling, the compressor start is delayed by a

30-second timer. During this delay, the motorized ball valve is set to 50% open to allow fluid flow

through the unit condenser. The compressor will start after the 30-second timer elapses.

Motorized Ball Valve Manual Mode: (Service/Service, Figure 126) Manual operation can be

selected to allow service personnel to control the motorized ball valve from the Liebert iCOM.

When Auto BV Control is selected, the motorized ball valve functions as it would be during normal

system operation.

When Manual BV Control is selected, the user must be careful in setting the MBV position because

the ball valves will remain in the position set in the Service menu until the control is switched back to

Auto or until a technician changes the valves to another manual position (the motorized ball valve in

manual mode can be set in 1% increments from fully closed to fully open). Low- or high-discharge

pressure may occur during this mode, depending on environmental conditions and the position of the

motorized ball valve.

The motorized ball valve is driven by a 2-10VDC proportional control signal: the valve is closed at

2VDC, 50% open at 6VDC and fully open at 10 VDC.

3.1.7 MBV Operation After Compressor is Turned Off

Once a compressor has stopped, the MBV control will continue to change the MBV position to

maintain system pressures for a maximum time of 10 minutes by following the Auto BV control

algorithm. When the 10-minute delay has expired or the discharge pressure is below its minimum

threshold, the motorized ball valve will close until the next compressor activation.

3.1.8 Service Offset—Changing System Pressure Settings

The MBV control is set to maintain a system pressure specific to the particular type of cooling unit. A

properly trained and qualified technician can increase or decrease the pressure through the Ball

Valve Setpoint Offset found in the Service/Options Setup menu. The range is 0 to 50 PSI; the default

is 30 PSI.

NOTE

Compressor operation will be delayed 30 seconds to allow the motorized ball valve to position

itself for initial startup.

NOTE

Adjusting this parameter will increase or decrease the operating compressor discharge

pressure by changing the targeted range of control. The discharge pressure is the peak pressure

of the digital cycle.

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Emerson Liebert iCOM User Manual Page 34

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