50
YORK INTERNATIONAL
Listed in Fig. 15 and 16 are the loading and unloading
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 maintaining
a leaving water temperature of 45°F. As mentioned be-
fore, 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 unloading
will take place as needed to keep water temperature in the
CONTROL RANGE between the TARGET and LOW LIMIT
WATER TEMPERATURE. As mentioned 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 programmed into memory using
the CHILLED LIQUID TEMP RANGE KEY. Usually this is
a window of water temperatures 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. 17 to aid in understanding the loading
and unloading scheme performed by the microprocessor.
Within the lower half of the CONTROL RANGE, the mi-
croprocessor will not call for any further loading or un-
loading unless the Rate Sensitivity is exceeded. If tem-
perature drop exceeds 1 X the Rate Sensitivity, the mi-
cro will unload the chiller to prevent overshoot.
FIG. 17 – 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
If leaving water temperature should fall into the tem-
perature range “BELOW THE CONTROL RANGE” which
is below the programmed Low Limit WATER TEMPERA-
TURE, the microprocessor will unload the chiller in 20
sec. intervals until water temperature rises back into the
CONTROL RANGE.
If temperature is in the upper half of CONTROL RANGE
or in the RATE CONTROL RANGE, the microprocessor
will continue loading the chiller as needed in 150 sec.
intervals until temperatures pass into the lower half of
the CONTROL RANGE. If the rate of drop in water
temperature exceeds 2X the programmed Rate Sensitiv-
ity, no further loading or unloading will result since the
micro sees the temperature dropping at an excessive
rate anticipating temperature will soon fall into the CON-
TROL RANGE.
When temperatures are in the temperature range
ABOVE THE RATE CONTROL RANGE, the micro will
load the chiller in intervals of 30 sec. to bring the tem-
perature down as quickly as possible. The micro is
capable of providing 5, 7, or 10 steps of loading/unload-
ing although 10 steps is not available with the compres-
sor is utilized. The chiller MUST be programmed for the
proper number of steps. See page 68. Otherwise, im-
proper operation and water temperature control prob-
lems will result.
NOTE: The micro controls loading and unloading re-
sponses on a 10 step scale regardless of the
number of stages present. Therefore, loading
and unloading responses on 5 & 7 step chillers
may appear delayed (time between steps in-
creased) when missing steps are activated or
de-activated by the micro, 5 STEP CONTROL
IS STANDARD.
Figs. 18 and 19 show the loading and unloading se-
quences for 5 and 7 steps of control. Although not cur-
rently available, 7 step control sequence is shown. This
option may be available in the future.
