approached, the control will proportionally limit the amount of capacity increase permitted and if
exceeded will issue unloading into the capacity control command.
Anti-surge minimum frequency
In order to maintain sufficient compressor lift to overcome condenser pressure and prevent surge
throughout operation, the control maintains and continuously updates a minimum limit for VSD
speed. This limit is the Active Anti-Surge Minimum Frequency. It is calculated and applied to the
speed each cycle of the capacity control routine.
Smart freeze
The Smart Freeze feature prevents nuisance chiller shutdowns due to brief periods of chilled liquid
flow fluctuations or other brief operating conditions that would normally cause Low Evaporator
Pressure Safety shutdowns. With this feature enabled and activated, the chiller is permitted to
ride through these temporary conditions. Also, this feature allows the Leaving Chilled Liquid
Temperature Setpoint to be set as low as 36.0ºF (2.2ºC). Smart Freeze protection can be enabled or
disabled at the Keypad, by a service technician. It cannot be used in Brine cooling mode.
Smart Freeze protection uses the Evaporator Refrigerant Temperature as one of the variables to
determine when freezing is imminent. The basis of this feature is that the chilled liquid contains an
amount of heat, which cannot be eliminated immediately. Therefore, it requires a certain amount of
time for the liquid to change to a solid. During this period of time, those parameters that determine
when solidification will occur are evaluated and the shutdown is based on accumulated time below
the freeze temperature.
Surge protection
The surge protection feature detects surge events. It provides a running count of the surges
detected over the lifetime of the chiller. It allows the user to define how many surges are excessive
and how the control will react to an excess surge condition. When excessive surging is detected,
this feature can shutdown the chiller.
Surge events are detected by monitoring the relationship between the Condenser pressure
and Evaporator pressure while the chiller is running. An excess surge condition is detected by
comparing the number of surge events that occur in a selectable time period to a selectable
threshold.
If the number of surge events (Surge Window Count) detected in the time period programmed as
the COUNT WINDOW setpoint (1 to 5 minutes; default 5) exceed the threshold programmed as the
COUNT LIMIT setpoint (4 to 20; default 4) an excess surge condition has been detected.
Unless the SHUTDOWN features have been enabled, as explained below, the chiller will continue to
run under the same conditions displaying WARNING – EXCESS SURGE DETECTED. This message
will be displayed until manually reset with the Warning Reset key in Operator access level. If the
SHUTDOWN setpoint is Enabled, when an excess surge condition has been detected a safety
shutdown will be performed and SURGE PROTECTION - EXCESS SURGE is displayed.
Head pressure control
The Head Pressure Control feature enables chiller control of a field-mounted facility condenser
water temperature control means, if one is necessary for prolonged cold water startup as described
in OptiView control center functions and navigation. YMC
2
chillers are capable of operation
within a wide range of condenser water temperatures. However, a low minimum condenser
water temperature, as specified in the YMC
2
Engineering Guide (Form 160.84-EG1), is required to
maintain sufficient pressure differential (head) between the condenser and evaporator for correct
refrigerant management in the chiller. The head pressure control function provides an analog
output control signal from the OptiView Control Center that responds to the programmed Head
Pressure (condenser pressure minus evaporator pressure) Setpoint. The 0-10 VDC or 4-20 mA
17
YMC
2
Mod B with OptiView
™
Control Center
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