FORM 150.60-NM3
49
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 com-
pletely off at a temperature of 45°F. thus maintaining 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 TARGET
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
temperatures of about 2 - 3°F. The micro will cause load-
ing 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
micro-processor will not call for any further loading or
unloading unless the Rate Sensitivity is exceeded. If
temperature drop exceeds 1X the Rate Sensitivity, the
micro will unload the chiller to prevent overshoot.
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 tempera-
ture exceeds 2X the programmed Rate Sensitivity, no
further loading or unloading will result since the micro
sees the temperature dropping at an excessive rate an-
ticipating temperature will soon fall into the CONTROL
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 ca-
pable of providing 5, 7, or 10 steps of loading/unloading
although 10 steps is not available with the compressors
utilized. The chiller MUST be programmed for the num-
ber of steps which are standard. See page 67. Other-
wise, improper operation and water temperature control
problems 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.
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
Summary of Contents for YCAJ44HE8
Page 16: ...16 YORK INTERNATIONAL WIRING DIAGRAMS LD02165 FIG 5 ELEMENTARY DIAGRAM...
Page 17: ...FORM 150 60 NM3 17 YORK INTERNATIONAL FIG 5 ELEMENTARY DIAGRAM Cont d LD02166...
Page 20: ...20 YORK INTERNATIONAL CONNECTION DIAGRAM ELECTRICAL BOX FIG 7 CONNECTION DIAGRAM LD02171...
Page 21: ...FORM 150 60 NM3 21 YORK INTERNATIONAL FIG 7 CONNECTION DIAGRAM Cont d LD02172...
