Control Method
The control utilizes an upper and lower pressure threshold with a 35psi (241kPa) deadband to reduce valve movement. If the liquid pressure is between the upper and lower threshold, the valve remains at the current position. If the liquid pressure exceeds the upper threshold the valve opens, and if the pressure falls below the lower threshold the valve closes. There are multiple adjustment bands to ease discharge pressure back into control range.
4.4.2Adjustment
Both pressure thresholds can be shifted simultaneously over a 50psi (345kPa) range (the 35psi [241kPa] differential remains constant). The ball valve setpoint offset parameter in the Liebert iCOM® Service menu can be adjusted from 0 to 50 PSI (345 kPa) to raise or lower the control band similar to the pressure adjustment on a water regulating valve. Changing the setpoint offset will adjust the pressure thresholds for both circuits. Units are
4.4.3Startup
The setpoint offset is adjusted to the minimum value during startup, then changes to the set value once the compressor reaches normal operating pressures. Changes in fluid temperature could cause pressure changes that do not result in valve movement within the deadband. Fan cycling stats should be set to prevent continuous fluid temperature swings greater than 10°F (5.6°C).
4.4.4Location
The motorized ball valve is located in the condenser fluid return line.
4.4.5Manual Control
The valve can be manually set by disconnecting AC power, depressing the manual override button on the valve actuator and adjusting the valve position with the handle. The motorized ball also can be controlled through the Liebert iCOM’s Service menu using manual mode to override the normal control.
41 | Liebert® Challenger 3000™ |