Schreiber Chillers 15 Med Main Manual - Manual (Page 14)

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 set-point. 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 set-point. 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 set-point. 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 set-point, 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.