Ice Mode Operation; Operator Interface Touch Screen; Navigation - McQuay WSC Operating Manual

Ice Mode Operation

If available modes is set to ICE only the chiller will start (at start delta t) and run the Ice cycle described as
follows: The chiller will ignore softload and all Demand limits and rapidly load up to Maximum Amps setpoint.
The compressor(s) do not unload. If the chiller has dual compressors (WDC), the lead compressor will unload
approx. one minute after starting to allow the second compressor to start (at reduced lift pressure), then both
compressors will load to Max Amps. When both compressors have achieved the Ice LWT setpoint both
compressors will shutdown. The Evap pump will continue to run and if the Evap LWT climbs to the Start Delta
T the chiller will restart this process.
The following failsafe feature has been incorporated into the code. If one compressor reaches the Stop Delta
Temp (below the setpoint) before the other compressor has achieved the setpoint, both compressors will
shutdown.
If available modes is set to Cool/Ice with Ice mode operation selected, the chiller will run one ICE cycle and
shutdown (compressors and pumps) no automatic restart allowed. When the operator switches the chiller from
Ice to Cool mode the chiller will reset for operation. Changing modes can be done through the OITS, switches
or BAS interface, which ever is selected.
Some sort of migration freeze protection needs to be in place when the chiller terminates ice mode. This is
usually sensed by the liquid line sensor and forces a condenser pump to circulate to prevent freeze up of the
condenser.

Operator Interface Touch Screen

Navigation

The home screen shown in VIEW screen on page 18 is usually left on (there is a screen-saver built in that is
reactivated by touching the screen anywhere). This VIEW screen contains the STOP and AUTO buttons used to
start and stop the unit when in Local control. Other groups of screens can be accessed from the Home screen by
pressing one of three buttons on the bottom of the screen; HISTORY, VIEW, SET.
• HISTORY will go to the last history screens viewed and can toggle between the two history screens.
• Trend History
• Alarm History
• VIEW will go to the next View screen and other sub-View screens used to look in detail at settings and the
operation of the chiller. Pressing View from any other screen will return to the Home View screen.
•
SET will go to a series of screens used to set setpoints.
The figure on the following page illustrates the arrangement of the various screens available on the OITS. A few
minutes practice on an actual OITS should provide a comfortable level of confidence in navigating through the
screens.
16 OM Centrif Micro ΙΙ-5