York YCWJ45EE0, Installation Operation & Maintenance, Page: 66 / 104

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YORK INTERNATIONAL
Listed in Fig. 18, 19 and 20 are the loading and unload-
ing sequences for 5, 7, and 10 steps of control. A typical
setpoint of 45°F with a cooling range of 10°F is shown
for example purposes. The chiller will be completely
loaded at a return water temperature of 55°F and will be
completely off at a temperature of 45°F, thus maintain-
ing a leaving water temperature of 45°F. As mentioned
before, loading/unloading timers as well as rate control
software must be satisfied before loading/unloading will
occur. This reduces the possibility of cycling.
LOADING AND UNLOADING
LEAVING WATER TEMPERATURE CONTROL
In leaving water temperature control, loading and un-
loading will take place as needed to keep water tem-
perature in the CONTROL RANGE between the TAR-
GET and LOW LIMIT WATER TEMPERATURE. As men-
tioned earlier in this manual, the CONTROL RANGE is
the temperature range of leaving water temperature that
is acceptable to the user and has been previously pro-
grammed into memory using the CHILLED LIQUID TEMP
RANGE KEY. Usually this is a window of water tempera-
tures of about 2° - 3°F. The micro will cause loading and
unloading actions to occur as needed to keep leaving
water temperatures in the lower half of this range. Refer
to Fig. 21 to aid in understanding the loading and un-
loading scheme performed by the microprocessor.
FIG. 20 – 10 STEP LOADING/UNLOADING (RETURN WATER CONTROL)
10 STEP
NOTE: The “Lead Comp + 2 Steps, Lag Compr Off” Step is skipped
on a temperature drop.
FIG. 21 – LEAVING WATER TEMPERATURE CONTROL
UPPER LIMIT OF
CONTROL RANGE
TARGET
LOW LIMIT WATER
TEMPERATURE
ABOVE THE RATE CONTROL RANGE
RATE CONTROL TEMP RANGE
CONTROL RANGE (CR)
BELOW THE CONTROL RANGE
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