Schreiber Chillers 1055AC/RC HANDBOOK - Manual (Page 15)

OPERATION
OVERVIEW OF OPERATING SEQUENCE:
During normal operation, both pumps will run continuously. The cryo-cooler pump continuously draws
water from the reservoir, pumps it to the cryo compressor, and back to the chilled water reservoir.
The GCHE pump does the same, except that the water runs through the two refrigeration system
evaporators before returning to the reservoir.
The 1055 controller monitors the temperature of the reservoir, and will cycle only one compressor
when the temperature rises above the setpoint. When there is no scan, the return temperature of
loop 2 will be approximately 15-25 degrees higher than the tank temperature. The return temperature
of loop 1 will be the same as the tank temperature. IN some cases it might be 1-3 degrees higher due
to ambient heat pickup.
When a scan is performed, the return temperature of loop 1 will rise rapidly. The controller senses
this temperature rise, and allows compressor 2 to be active. Compressor 2 will now cycle with
compressor 1 when the tank temperature rises above the setpoint. When the scan is finished, the
return temperature will drop. Compressors 1 and 2 will continue to cycle until the tank temperature is
below the setpoint. After they shutoff, compressor 2 will return to standby mode, and will not become
active again until the next rise in return 2 temperature.
Compressor Rotation
During normal operation it is possible that the 1055AC will only see a small heat load from the
cryo compressor. To prevent the same compressor from cycling all of the time, the 1055 alternates
the load between the two compressors. This is called compressor rotation. In forward rotation,
compressor 1 maintains the reservoir temperature, and compressor 2 cycles based on the rise in
return temperature form pump loop #1. Reverse rotation is the opposite.
Every time that a compressor cycles off when trying to maintain the tank temperature, the controller
will switch rotation. If the chiller starts out in forward rotation, compressor 1 will cycle, pull the
temperature down, and then shut off. Rotation is then reversed. The next time the temperature
rises above the setpoint, compressor 2 will cycle. During either rotation direction, when the return
temperature rises, the compressor not currently running will be enabled.
If either compressor is disabled, the controller will automatically disable rotation and select the proper
rotation.
CHILLER SYSTEMS:
CHILLED WATER CIRCUIT: