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33
Dual Chiller Control
The dual chiller function allows for master/slave control of two
units installed in parallel or series arrangement supplying
chilled fluid on a common loop. The chillers must be linked by
the Carrier Comfort Network
®
network and operate on the
same bus.
When the units are installed for parallel operation and chilled
water control is done on the outlet side of the units, the dual
chiller accessory kit (P/N 00EFN900044000A) is required. The
kit includes additional leaving fluid temperature thermistors
that must be installed on the common chilled water leaving
piping as described in the Installation Instructions for the kit.
The leaving fluid temperature sensors will be connected to
each chiller as described in the installation instructions. When
the chilled water control is done on the inlet side of the parallel
units no additional temperature sensor is required. See the
Field Wiring section in the 30XV Installation Instructions for
dual chiller LWT sensor control wiring. When chillers are con-
figured to operate in series mode no additional chilled water
temperature sensor is required.
The master chiller will monitor all external commands such as
start/stop, demand limiting, or set point select, and needs to be
started in Master operating type. The commands are transmitted
automatically to the slave unit, which must operate in CCN (Net-
work) mode. The slave chiller has no action in the master/slave
operations; it will only verify that CCN communication with the
master chiller is correct. If the master chiller is turned off while the
master/slave function is active, then the slave chiller will be
stopped. Under certain circumstances, the slave unit may be start-
ed first to balance the run times of the two units. In the event of a
communication failure between the two units, each unit will return
to an autonomous operating mode until the fault is cleared. If the
master unit is stopped due to an alarm, the slave unit is authorized
to start and therefore the slave unit configurations should be veri-
fied with desired set points.
The CCN communication port for the Master and Slave
chillers must be joined using a shielded cable in order to avoid
communication issues.
The master/slave linkage will not be allowed to operate if any
one of the slave chiller
CTRL_PNT
,
DEM_LIM
,
LAG_LIM
,
or
LCW_STPT
variables has a force priority higher than a
control force. In that case, the master/slave operations will not
be allowed or will be disabled.
The control algorithm relies on several parameters that must be
field configured for operation. Both chillers must be on the
same CCN bus with different addresses. On both chillers, Mas-
ter/Slave Select (
Main Menu
Configuration Menu
Master/Slave Config
Master/Slave Select
) must be enabled
(set to 1 [Master] or 2 [Slave]). The water piping arrangement
must be specified with the Chiller in Series variable (
Main
Menu
Configuration Menu
Master/Slave Config
Chiller in Series
). The Master chiller must be programmed
with the Slave Address (
Main Menu
Configuration Menu
Master/Slave Config
Slave Address
). Additional option-
al programming parameters may be configured to meet appli-
cation requirements.
The Lead Lag Select variable (
Main Menu
Configuration
Menu
Master/Slave Config
Lead Lag Select
) determines
which chiller is the lead machine. The options are: Always Lead,
Lag Once Failed Only, and Lead/Lag Runtime Select. Under Run-
time Select control, the lead chiller will change based on the time
increment selected in the Lead/Lag Balance Delta configuration
(
Main Menu
Configuration Menu
Master/Slave Config
Lead/Lag Balance Delta
). If the run hour difference between
the master and the slave remains less than the Lead/ Lag Balance
Delta, the chiller designated as the lead will remain the lead
chiller. The Lead/Lag changeover between the master and the
slave chiller due to hour balance will occur during chiller operat-
ing odd days, such as day 1, day 3, and day 5 of the month, at
12:00 a.m. If a lead chiller is not designated, the master chiller will
always be designated the lead chiller.
The dual chiller control algorithm has the ability to delay the
start of the lag chiller in two ways. The Lead Pulldown Time
parameter (
Main Menu
Configuration Menu
Master/
Slave Config
Lead Pulldown Time
) is a one-time delay ini-
tiated after starting the lead chiller, before checking whether to
start an additional chiller. This time delay gives the lead chiller
a chance to remove the heat that the chilled water loop picked
up while inactive during an unoccupied period. The second
time delay, Lead/Lag Start Timer (
Main Menu
Configura-
tion Menu
Master/Slave Config
Lead/Lag Start Timer
)
is a time delay imposed between the last stage of the lead
chiller and the start of the lag chiller. This prevents enabling
the lag chiller until the lead/lag delay timer has expired.
A quicker start of the lag chiller can be accomplished by con-
figuring the Lag Unit Pump Control parameter (
Main Menu
Configuration Menu
Master/Slave Config
Lag Unit
Pump Control
). If the difference between the common leaving
water temperature and the set point is greater than the config-
ured value, then the lag chiller will start.
A minimum on time for the lag chiller can be programmed
with the Lag Minimum Running Time configuration (
Main
Menu
Configuration Menu
Master/Slave Config
Lag Minimum Running Time
). This parameter causes the
control to run the lag chiller for the programmed minimum on
time. The Lag Unit Pump Control (
Main Menu
Configura-
tion Menu
Master/Slave Config
Lag Unit Pump Con-
trol
) can be configured such that the pump can be on or off
while the chiller is off. This parameter is only active in Parallel
Chiller Operation.
The lead chiller is started first and the lag chiller will be main-
tained at zero percent capacity through master forcing the lag
demand limit value (
LAG_LIM
) to 0%. The lag water pump
will be maintained off. When the lead chiller cannot be loaded
anymore (because it is loaded at its full available capacity or at
the master demand limit value) then the lag start timer is start-
ed. When the lag start time has elapsed, if the error on the mas-
ter controlled set point is greater than the dead band (
start_di
)
and if the pulldown time is elapsed, then the lag chiller water
pump will be turned on (if required by configuration) and the
lag chiller will be allowed to start through the master chiller
forcing the lag chiller demand limit value (
LAG_LIM
) to its
own demand limit value. To ensure that the lag chiller will be
unloaded first in case of water load decrease, the lead chiller
set point error will be reset downwards by 4°F (2.2°C) provid-
ed that the lead capacity is not zero.
Each dual chiller application, Parallel and Series, is described
separately below.
DUAL CHILLER CONTROL FOR PARALLEL APPLICA-
TIONS
To configure the master chiller for parallel applications, see Ta-
ble 26. To configure the slave chiller for parallel applications,
see Table 27.
Summary of Contents for AquaForce 30XV140
Page 79: ...79 Fig 76 VFD Communication Wiring Compressor A B Fan VFD A1 A2 B1 B2...
Page 228: ...228 Fig 90 30XV Typical Field Wiring Schematic cont...
Page 229: ...229 Fig 91 30XV Standard Tier 140 275 All Voltages Power Schematic NOTE See Legend on page 226...
Page 230: ...230 Fig 92 30XV Standard Tier 300 325 All Voltages Power Schematic NOTE See Legend on page 226...
Page 240: ...240 Fig 99 30XV Communication Wiring...
Page 241: ...241 Fig 100 30XV 115V Control Wiring All Tonnages All Voltages...
Page 242: ...242 Fig 101 30XV 24V Control Wiring 30XV140 325 All Voltages...
Page 243: ...243 Fig 101 30XV 24V Control Wiring 30XV140 325 All Voltages cont...
Page 244: ...244 Fig 102 30XV 24V Control Wiring 30XV350 500 All Voltages...
Page 245: ...245 Fig 102 30XV 24V Control Wiring 30XV350 500 All Voltages cont...
Page 246: ...246 Fig 103 Component Arrangement Diagram for 30XV140 325...
Page 247: ...247 Fig 103 Component Arrangement Diagram for 30XV140 325 cont...
Page 248: ...248 Fig 104 Component Arrangement Diagram for 30XV350 500...
Page 337: ...337 APPENDIX J FACTORY SUPPLIED PUMPS cont Fig L System Information...
Page 338: ...338 APPENDIX J FACTORY SUPPLIED PUMPS cont Fig M Unit and Language Settings...
Page 341: ...341 APPENDIX J FACTORY SUPPLIED PUMPS cont Fig P Data Input 2...
Page 342: ...342 APPENDIX J FACTORY SUPPLIED PUMPS cont Fig Q Data Input 3...
Page 347: ...347 APPENDIX J FACTORY SUPPLIED PUMPS cont Fig U Pump Wiring Diagram...