Compressor Capacity Loading Sequence - York MILLENNIUM YCAR0315 Installation Operation & Maintenance

Micro Panel
ing/unloading control algorithm allows the micro addi-
tional anticipatory loading and unloading capabilities
within the control range, based on the rate of chilled
liquid temperature change and the approach of safety
thresholds.
Control by "return" chilled liquid temperature is not an
option on this chiller.

6.6 COMPRESSOR CAPACITY LOADING SEQUENCE

Each compressor will be cycled through three stages of
loading regardless of the number of cylinders (4, 6 or
8). These stages are designated as Stage 0, 1 and 2.
Compressor capacity will be staged according to the
table below:
CMPR
STAGE
CYLINDER CYLINDERS
0
4 1
2
0
6 1
2
0
8 1
2
The microprocessor will attempt to control the leaving
chilled liquid temperature to the setpoint +/- the Range,
which defines the upper and lower limits of the Control
Range. The Control Range specifies the desired tem-
perature range that is acceptable for a specific chilled
liquid application.
When power is first applied, the microprocessor will
begin counting down a 2-minute "power-up" timer. This
timer prevents repeat motor starts after a power failure
and reduces the possibility of overheating the motor.
After the 2-minute power-up timer times out, a start
sequence will initiate when all run permissives are sat-
isfied, no faults exist, the Daily Schedule is calling for
chiller operation, and a cooling load exists.
When the start-up timer has counted to "0", if the
leaving chilled liquid temperature is above the high end
of the control range, the lead compressor will start at
"Stage 0". In addition, the liquid line solenoid of the lead
compressor will energize immediately on start. A 60-
second anti-coincidence timer will always assure that
another compressor will not start for a period of at least
one minute. The Load Timer will reset to 60 seconds,
and the Unload Timer to 30 seconds.
136
NO. OF
CAPACITY
2 50%
4 100%
4 100%
2 33%
4 66%
6 100%
4 50%
6 75%
8 100%
After one minute of operation and the load timer has
counted down to "0", and if the chilled liquid temperature
is above the high end of the control range, the micro will
load the lead compressor. The lead compressor now loads
to "Stage 1". The Load Timer will reset to 60 seconds
and the Unload Timer to 30 seconds.
After 2 minutes of operation and the load timer has
counted down to "0", and if the chilled liquid temperature
is above the high end of the control range, the micro will
load the lead compressor. The lead compressor now loads
to "Stage 2". The Load Timer will reset to 60 seconds
and the Unload Timer to 30 seconds.
After 5 minutes of operation and the load timer has
counted down to "0", and if the chilled liquid temperature
is above the high end of the Control Range, the lag com-
pressor will start ("Stage 0") and the lead compressor
will fully unload ("Stage 0"). The Load Timer will reset
to 60 seconds and the Unload Timer to 30 seconds.
After 6 minutes of operation and the load timer has
counted down to "0", and if the chilled liquid temperature
is above the high end of the control range, the micro will
load the lead compressor to "Stage 1". The lag compres-
sor remains unloaded. The Load Timer will reset to 60
seconds and the Unload Timer to 30 seconds.
After 7 minutes of operation and the load timer has
counted down to "0", and if the chilled liquid temperature
is above the high end of the control range, the micro will
load the lag compressor to "Stage 1". The lead compres-
sor remains at "Stage 1". The Load Timer will reset to 60
seconds and the Unload Timer to 30 seconds.
After 8 minutes of operation and the load timer has
counted down to "0", and if the chilled liquid temperature
is above the high end of the control range, the micro will
load the lead compressor to "Stage 2". The lead com-
pressor remains at "Stage 1". The Load Timer will reset
to 60 seconds and the Unload Timer to 30 seconds.
After 9 minutes of operation and the load timer has
counted down to "0", and if the chilled liquid temperature
remains above the high end of the control range and the
load timer has counted down to "0", the lag compressor
will load to "Stage 2". The lead compressor remains
loaded to "Stage 2". The Load Timer will reset to 60
seconds and the Unload Timer to 30 seconds. The chiller
is now fully loaded.
Once temperature is satisfied and the chiller is loaded
to a capacity less than full load, the micro will load the
compressor with the lowest stage of loading if tempera-
ture rises above the high end of the Control Range and
FORM 150.52-NM2 (1001)
YORK INTERNATIONAL