CVGF-SVU02B-E4
67
Evaporator Limit
Evaporator refrigerant
temperature is continuously
monitored to provide a limit
function that prevents low
refrigerant temperature trips.
This allows the chiller to
continue to run at a reduced
load instead of tripping off at the
Low Refrigerant Temperature
Cutout Setpoint (LRTC).
Evaporator limit could occur
with an initial pulldown of a loop
temperature where the
condenser is colder than the
evaporator (inverted start), and
the evaporator refrigerant
temperature may drop below the
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. It 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 (1.1°C).
When actively limiting machine
control “Evaporator
Temperature Limit” will be
displayed as a suboperating
mode.
Leaving Water Temperature
Cut-out
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 at 36°F (2.2°C)
however is adjustable with
TechView
™
. The cut-out strategy
is illustrated in Figure 23.
The Leaving Water Temperature
Cut-out Setpoint is
independently adjustable from
the chilled water setpoint.
Shutdown of the compressor
due to violation of the Leaving
Water Temperature Cut-out
results in an automatically
resettable diagnostic (MAR). The
DynaView
™
Operating Mode
indicates when the Leaving
Water Temperature Cut-out
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 (0.94°C). (See Cut-out
Strategy Figure 23.) When either
difference is violated, the CH530
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 Cut-out Setpoint
for 30°F (16.7°C) seconds the
chiller will shutdown and
indicate a diagnostic.
Low Refrigerant
Temperature Cut-out
The purpose of the low
evaporator refrigerant
temperature protection is to
prevent water in the evaporator
from freezing. When the LRTC
trip point is violated, a latching
diagnostic indicating the
condition is displayed. The LRTC
Diagnostic is active in both the
Running and Stopped modes.
Machine Protection and
Adaptive
Summary of Contents for CVGF 1000
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