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Differential to Start/Stop
With the chiller in Auto mode waiting for a need to cool and
the leaving water temperature (Leaving Water
Temperature) reaches the
Differential-to-Start
setpoint, the
chiller start sequence is initiated as the Leaving Water
Temperature reaches the
Differential-to-Stop
setpoint. The
chiller returns to the AUTO mode waiting for a need to cool
mode after completing a solution dilution cycle (Reference
Figure 28).
•
Differential-to-start is the number of degrees above the
chilled water setpoint that the return water temperature
must increase to start the chiller. The differential-to-start
setpoint is LCD menu adjustable from 1 to 10°F (0.5 to
5.55°C).
•
Differential-to-stop is the number of degrees below the
chilled water setpoint that the supply water temperature
drops before the chiller shuts down. The differential-to-
stop setpoint is adjustable on the LCD from -1 to -10°F
(-0.5 to -5.55°C).
•
Both are integrated functions to avoid nuisance start or
stops on momentary fluctuations in temperature.
•
Both setpoints move with respect to the active chilled
water setpoint.
•
Differential-to-stop must be set above low leaving water
temperature cutout setpoint, otherwise cutout occurs
before differential to stop occurs.
•
Differential-to-stop must be set above evaporator low
refrigerant temperature limit control, otherwise limit
functions become active before differential to stop is
reached.
Figure 28. Example illustrating the leaving water temperature
setpoint and the differential to start and stop setpoints
Differential to start.
(for example if 3°F then 47°F in this example).
Leaving Water Temperature
Setpoint
(for example 44°F)
Differential to stop.
(for example, if 2°F, then 42°F in this example)