Machine Protection
and Adaptive
Control
Evaporator Limit
Evaporator refrigerant temperature is continuously monitored to provide a limit function that prevents low refrigerant temperature trips which allows the chiller to continue to run at a reduced load instead of tripping off at the Low Evaporator Refrigerant Temperature Cutout Setpoint (LRTC).
Evaporator limit could occur with an initial pull down of a loop where the Condenser is colder than the Evaporator (Inverted Start), the Evaporator refrigerant temperature may drop below the Low Refrigerant Temperature Cutout (LRTC). This limit prevents the unit from shutting down on a diagnostic during this type of pulldown. Another example is a Chiller that is low on refrigerant charge will run with low Evaporator refrigerant temperatures. This limit allows the chiller to continue to run at a reduced load.
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Evaporator Limit uses the Evaporator Refrigerant Temperature sensor in a PID algorithm (Similar to the Leaving Water Temperature control) that allows the chiller to run at the LRTC + 2 degree F.
When actively limiting machine control “Evaporator Temperature Limit” will be displayed as a sub- operating mode.
Leaving Water Temperature Cutout
Leaving water temperature cutout is a safety control that protects the chiller from damage caused by water freezing in the evaporator. The cutout setpoint is factory set however is adjustable with the Service tool.
The “Leaving Water Temperature Cutout Setpoint” is independently adjustable from the chilled water setpoint and factory set. Shutdown of the compressor due to violation of the Leaving Water Temperature
Cutout results in an automatically resettable diagnostic (MAR). The DynaView™ Operating Mode indicates when the “Leaving Water Temperature Cutout Setpoint” conflicts with the chilled water temperature setpoint by a message on the display. The “Leaving Water Temperature Cutout Setpoint” and chilled water setpoint, both active and front panel, are separated by a minimum of 1.7°F. See Cutout Strategy, Figure 27. When either difference is violated, the UCP does not permit the above differences to be violated and the display exhibits a message to that effect and remains at the last valid setpoint. After violation of the “Leaving Water Temperature Cutout Setpoint” for 30°F seconds the chiller will shutdown and indicate a diagnostic.