![background image](http://html1.mh-extra.com/html/carrier/aquasnap-30rba315/aquasnap-30rba315_controls-start-up-operation-service-and-troubleshooting-instructions_2561847020.webp)
20
The Lag Unit Pump Select configuration must be set
consistently. If pump control is NOT being used, set
Con-
figuration
RSET
LAGP
to
1
. If pump control IS being
used, set
Configuration
RSET
LAGP
to
0
, which is the
default value. This must be set in both the master and slave
chillers, and it must be consistent in both.
Capacity Control —
The control system cycles com-
pressors and minimum load valve solenoids (if equipped) to
maintain the user-configured leaving chilled fluid temperature
set point. Entering fluid temperature is used by the main base
board (MBB) to determine the temperature drop across the
cooler and is used in determining the optimum time to add or
subtract capacity stages. Entering fluid temperature, space
temperature (requires additional sensor), or outdoor-air temper-
ature reset features can automatically reset the leaving chilled
fluid temperature set point. It can also be reset from an external
4 to 20-mA signal (requires energy management module).
The control has an automatic lead-lag feature built in for
circuit and compressor starts. If enabled, the control will deter-
mine which circuit (
Configuration
OPTN
LLCS
=
0
) and
compressor to start to even the wear. The compressor wear
factor (combination of starts and run hours) is used to deter-
mine which compressor starts.
Compressor Wear Factor = (Compressor Starts)
+ 0.1
(Compressor Run Hours)
In this case, the circuit with the lowest average compressor
wear factor (the average of the wear factors of all available
compressors in the circuit) is the circuit that starts first. The
compressor within the circuit with the lowest wear factor is the
first to start. If the automatic lead-lag function for the circuit is
not enabled [
Configuration
OPTN
LLCS
=
1
(Circuit A
leads),
2
(Circuit B leads), or
3
(Circuit C leads)], then the se-
lected circuit will be the first to start. Again, the compressor
with the lowest wear factor within the circuit will be the first to
start. If Minimum Load Control is enabled (
Configuration
UNIT
HGBP
=
1
), the valve will be operational only during
the first stage of cooling.
Once the lead compressor has been started, the lag compres-
sors will be determined by the wear factor and loading
sequence selected. If equal loading is selected, (
Configura-
tion
OPTN
LOAD
=
0
), the circuit with the lowest average
wear factor for the available compressors will start next, with
the compressor with the lowest wear factor starting. The con-
trol will attempt to keep all circuits at approximately the same
number of compressors ON. For this option to function proper-
ly, all circuits must have the same number of compressors
available. If a circuit compressor is not available due to an
alarm condition or demand limit, the capacity staging will
change to staged. If staged loading is selected, (
Configura-
tion
OPTN
LOAD
=
1
), the started circuit will continue to
turn on compressors according to the lowest wear factor until
all are on, then start the next circuit with the lowest average
wear factor. If Minimum Load Control is enabled for close
control (
Configuration
UNIT
HGBP
=
2
), the valve will be
available at all stages for better temperature control. If
Minimum Load Control is enabled for high ambient control
(
Configuration
UNIT
HGBP
=
3
), the valve will be used
only when a high pressure override is active for that circuit.
The electronic expansion valves provide a controlled start-
up. During start-up, the low pressure logic in the lead circuit
will be ignored for 5
minutes to allow for the transient changes
during start-up. As additional stages of compression are
required, the processor control will add them. The following
example is based on a 30RB225 machine, which has three
25-ton compressors in each circuit. See Table 15.
Each example below has different configurations and is
intended to illustrate the loading sequences possible for normal
operation.
In Example 1 (Table 16), assume the following configurations
are in place:
Configuration
UNIT
HGBP
=
1
. . Minimum Load Control
installed and enabled for Start-Up Only
Configuration
OPTN
LOAD
=
0
. . . .Equal Circuit Loading
Configuration
OPTN
LLCS
=
0
. .Automatic Circuit Select
Since Circuit A has the lowest average wear factor, it will be
the lead circuit. Within the circuit, compressor A3 has the
lowest wear factor and will start first with Minimum Load
Control ON. The next stage will turn OFF the minimum load
control. Stage 3 will start another circuit because of the Equal
Circuit Loading configuration. The next circuit with the lowest
wear factor is Circuit B, and the compressor with the lowest
wear factor is B2. The next stage will be a circuit C compres-
sor. The process continues until all compressors are ON. See
Table 16.
In Example 2 (Table 17), assume the compressor starts and
run hours are the same as in the previous example and the
following configurations are in place:
Configuration
UNIT
HGBP
=
1
. . Minimum Load Control
installed and enabled for Start-Up Only
Configuration
OPTN
LOAD
=
1
. . . Staged Circuit Loading
Configuration
OPTN
LLCS
=
0
. .Automatic Circuit Select
Since Circuit A has the lowest average wear factor, it will be
the lead circuit. Within the circuit, compressor A3 has the
lowest wear factor and will start first with Minimum Load
Control ON. The next stage will turn OFF the minimum load
control. Stage 3 will start a compressor in the same circuit be-
cause of the Staged Circuit Loading configuration. Compressor
A2 has the next lowest wear factor and will be started next.
Compressor A3 will be next to start. Since all compressors in
Circuit A are ON, the next stage will start another circuit. Of
the remaining circuits, Circuit B has the lowest wear factor, and
the compressor with the lowest wear factor is B2. All of the
Circuit B compressors will be started in the same manner as
Circuit A. Once all Circuit B compressors are ON, then Circuit
C will be started. The process continues until all compressors
are ON. See Table 17.
Table 15 — Compressor Starts and Run Hours
COMPRESSOR
STARTS
RUN HOURS
WEAR FACTOR
CIRCUIT AVERAGE
WEAR FACTOR
A1
25
249
49.9
44.8
A2
22
237
45.7
A3
26
128
38.8
B1
41
453
86.3
67.6
B2
38
138
51.8
B3
35
297
64.7
C1
93
103
103.3
80.3
C2
57
98
66.8
C3
61
99
70.9
Summary of Contents for AQUASNAP 30RBA315
Page 77: ...77 Fig 37 Control Schematic 30RB060 080 a30 4619...
Page 78: ...78 Fig 38 Control Schematic 30RB090 150 a30 4620...
Page 79: ...79 Fig 39 Control Schematic 30RB160 190 a30 4622...
Page 80: ...80 Fig 40 Control Schematic 30RB210 300 a30 4622...
Page 81: ...81 Fig 41 Heat Reclaim Control Schematic a30 4622...