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TOTAL
STAGE
CAP.
Cir. Cap.
0
0
1
8
2
11
3
22
33
4
33
33
5
44
33
6
55
66
7
66
66
8
77
66
9
88
100
10
100
100
LEGEND
MLC — Minimum Load Control
TOTAL
STAGE
CAP.
Cir. Cap.
0
0
1
8
2
11
3
22
4
33
5
44
33
6
55
66
7
66
100
8
77
100
9
88
100
10
100
100
LEGEND
MLC — Minimum Load Control
The capacity control algorithm runs every 30 seconds. The
algorithm attempts to maintain the Control Point at the desired
set point. Each time it runs, the control reads the entering and
leaving fluid temperatures. The control determines the rate at
which conditions are changing and calculates 2 variables based
on these conditions. Next, a capacity ratio (SM2) is calculated
using the 2 variables to determine whether or not to make any
changes to the current stages of capacity. This ratio value
ranges from –100 to +100%. If the next stage of capacity is a
compressor, the control starts (stops) a compressor when the
ratio reaches +100% (–100%). If the next stage of capacity
is the Minimum Load Control, the control energizes (deener-
gizes) the Minimum Load Control when the ratio reaches
+60% (–60%). If installed, the minimum load valve solenoid
will be energized with the first stage of capacity. The control
will also use the minimum load valve solenoid as the last stage
of capacity before turning off the last compressor. If the close
control feature (Configuration
abled the control will use the minimum load valve solenoid
whenever possible to fine tune leaving fluid temperature con-
trol. A delay of 90 seconds occurs after each capacity step
change with Minimum Load Control. A delay of 3 minutes oc-
curs after each compressor capacity step change.
BRINE CHILLER OPERATION — For chiller sizes 120 to
390 with the factory-installed brine option, discharge and liq-
uid line solenoids are added to all circuits (Circuit B only for
size 120). The control system must be correctly configured for
Table 18 — Compressor Stage and Circuit Cycling, Example 3
CIRCUIT A
MLC
A1
A2
A3
0
0
X
0
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
Table 19 — Compressor Stage and Circuit Cycling, Example 4
CIRCUIT A
MLC
A1
A2
A3
0
0
0
0
0
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
UNIT
HGBP=2) is en-
CIRCUIT B
Cir. Cap.
MLC
B1
B2
0
24
X
X
33
X
33
X
33
X
66
X
66
X
66
X
100
X
X
100
X
X
100
X
X
NOTES:
1. Total Cap. (Total Unit Capacity) and Cir. Cap. (Circuit Capacity)
are approximate percentage values.
2. Example is to determine minimum load control, staged circuit
loading, and automatic circuit select.
CIRCUIT B
Cir. Cap.
MLC
B1
B2
0
0
0
0
0
0
0
0
33
X
66
X
100
X
X
NOTES:
1. Total Cap. (Total Unit Capacity) and Cir. Cap. (Circuit Capacity)
are approximate percentage values.
2. Example is to determine minimum load control, staged circuit
loading, and automatic circuit select.
proper operation. The minimum load valve option must be en-
abled (Configuration
must be set to medium temperature brine (Configuration
SERV
FLUD=2). The discharge and liquid line solenoid
valves are wired in parallel so they will both open and close at
the same time. The main function of the solenoid valves is to
isolate a portion of the condenser section when only a single
compressor is running to allow for proper oil return to the com-
pressors. A chart showing solenoid operation is shown below:
CIRCUIT CAPACITY
All compressors off
One compressor starting
Two or more compressors
running
Reduction from two to one
compressor running
CAPACITY CONTROL OVERRIDES — The following ca-
pacity control overrides (Run Status
modify the normal operation routine. If any of the following
override conditions listed below is satisfied, it will determine the
capacity change instead of the normal control.
Override #1: Cooler Freeze Protection — This override at-
tempts to avoid the freeze protection alarm. If the Leaving
Water Temperature is less than Brine Freeze Set Point
22
CIRCUIT C
B3
Cir. Cap.
MLC
C1
0
0
0
0
33
X
33
X
33
X
66
X
66
X
66
X
100
X
CIRCUIT C
B3
Cir. Cap.
MLC
C1
0
24
X
33
66
100
X
100
X
100
X
100
X
100
X
X
100
X
X
100
X
UNIT
HGBP=1) and the fluid type
DISCHARGE/LIQUID SOLENOID
VALVE OPERATION
Solenoids energized
Solenoids deenergized after
30-second delay
Solenoids energized
Solenoids deenergized with no
delay
VIEW
C2
C3
X
X
X
X
X
X
X
X
X
X
X
C2
C3
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
CAP.S) will
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