Schreiber Chillers 15MEDAC email - Manual (Page 24)

OPERATION
OVERVIEW OF OPERATING SEQUENCE:
The 15MEDGEN2 chiller is a 15 ton air cooled chiller designed specifically for the
Medical Cooling application. The chiller consists of dual equal circuit refrigeration
system, large chilled water reservoir, dual redundant chilled water pumps, variable
speed condenser fans, and an advanced microprocessor controller.
During normal operation, one pump will run continuously. The pump continuously
draws water from the reservoir, pumps it to the external heat exchanger, through
chiller evaporator heat exchanger then back to the chilled water reservoir.
The chiller controller monitors the temperature of the reservoir, and will cycle only one
compressor when the temperature rises above the set-point. When the return
temperature is raised above the TEMP RISE set-point, the second comes on.
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 temperature.
Compressor Rotation
During normal operation it is possible that the chiller will only see a small heat load. To
prevent the same compressor from cycling all of the time, the controller 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.