Trane CenTraVac Duplex CDHE, Operation & Maintenance Manual

Page: 76 / 116

CDHF-SVU01C-EN
76
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.
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.
Machine Protection
and Adaptive
Control