YORK INTERNATIONAL
10
FORM 160.54-O2(1102)
FORM 160.54-O2(1102)
11
YORK INTERNATIONAL
2
FIG. 4 –
CHILLER STARTING SEQUENCE & SHUTDOWN SEQUENCE
(VARIABLE SPEED DRIVE)
LD04130
CHILLER OPERATION
After the compressor reaches its operating speed, the
Prerotation Vanes will begin to open under the control
of the Microprocessor Board which senses the leav-
ing chilled liquid temperature. The unit capacity will
vary to maintain the leaving
CHILLED LIQUID
TEMPERATURE
setpoint. The Prerotation Vanes
are modulated by an actuator under the control of
the Microprocessor Board. The vane control routine
employs proportional plus derivative (rate) control
action. A drop in chilled liquid temperature will cause
the actuator to close the Prerotation Vanes to decrease
chiller capacity. When the chilled liquid temperature
rises, the actuator will open the Prerotation Vanes to
increase the capacity of the chiller.
However, the current draw (amperes) by the com-
pressor motor cannot exceed the setting of the
%
CURRENT LIMIT
at any time during the unit
operation, since the Microcomputer Control Center
40 to 100% three-phase peak current limit software
function, plus the 3-phase 100% solid state overload
current limiter (CM-2), on Electro-Mechanical Starter
applications, or the Solid State Starter current Limit
function will override the temperature control func-
tion and prevent the Prerotation Vanes from opening
beyond the
% CURRENT LIMIT
setting.
** NOT FOR ALL SHUTDOWNS. REFER TO “DISPLAY MES-
SAGES” SECTION OF THIS MANUAL.
System Operating Procedures
If the load continues to decrease, after the Prerotation
Vanes are entirely closed, the chiller will be shut down
by the Leaving Chilled Liquid – Low Temperature
Control.
CONDENSER WATER TEMPERATURE CONTROL
The YORK MaxE
TM
chiller is designed to use less
power by taking advantage of lower than design
temperatures that are naturally produced by cooling
towers throughout the operating year. Exact control of
condenser water such as a cooling tower bypass, is not
necessary for most installations. The chiller requires
only that the minimum condenser water temperature
be no lower than the value
determined by referring to the formula below:
where:
Min. ECWT = LCWT – C RANGE + 17ºF
Min. ECWT = LCWT – C RANGE + 9.4ºC
ECWT = Entering Condensing Water Temperature
LCWT = Leaving Chilled Water Temperature
C Range = Condensing water temperature range at the
given load condition.
