79
Filtered Setpoint Feature
The micro utilizes a filtered chilled water setpoint feature.
Figure 29 illustrates a typical front panel setpoint change
from 44 to 50°F. The first illustration is without a filtered
setpoint feature and the second figure is with the filtered
feature.
Without a filtered setpoint change the chiller would cycle
off because of the 4°F differential to stop being reached
immediately. (Vertical rises shown in third figure).
The filtered setpoint feature allows the operator to change
the chilled water set point without a chiller shutdown.
The micro response to a loss of chilled waterload does not
have the same filtered setpoint associated with it. Rapid
load changes will simply be presented to the Differential to
Stop logic as large difference between the chilled water
setpoint and the leaving water temperature.
Figure 29. Three examples of setpoint changes with and without
the filter feature
Each of the differential control
functions is softened with an
integration of time and
temperature difference from the
chilled water setpoint.
Setpoint Changes Without Filter feature
Chilled Water Setpoint change greater than differential to stop.
Would cause the unit to shutdown on diff
to stop setpoint
Differential to stop.
Both cases assume the Differential to Stop Setpoint = 4 Deg F
Setpoint Changes With Filter feature
Differential to stop follows
filtered setpoint change to
prevent stop on setpoint
changes.
Front Panel Chilled
Water Setpoint
Degree F
Leaving Chilled Filtered Water
Differential With Filtered Chilled Water Setpoint Will Not cause the unit to cycle off.
Time
Assume the Differential to Stop Setpoint = 4°F
Front Panel Chilled Water Setpoint = Filtered Chilled Water
Degree F
Differential to Stop
Chiller is Cycled
Leaving Chilled Water
Time
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