Carrier AquaForce B Series Controls, Start-up, Operation, Service And Troubleshooting Instructions

Also see for AquaForce 30XV140: Controls, start-up, operation, service and troubleshooting instructions

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Carrier AquaForce B Series Controls, Start-up, Operation, Service And Troubleshooting Instructions Manual pdf 33 page image

33Dual Chiller ControlThe dual chiller function allows for master/slave control of twounits installed in parallel or series arrangement supplyingchilled fluid on a common loop. The chillers must be linked bythe Carrier Comfort Network ® network and operate on thesame bus.When the units are installed for parallel operation and chilledwater control is done on the outlet side of the units, the dualchiller accessory kit (P/N 00EFN900044000A) is required. Thekit includes additional leaving fluid temperature thermistorsthat must be installed on the common chilled water leavingpiping as described in the Installation Instructions for the kit.The leaving fluid temperature sensors will be connected toeach chiller as described in the installation instructions. Whenthe chilled water control is done on the inlet side of the parallelunits no additional temperature sensor is required. See theField Wiring section in the 30XV Installation Instructions fordual chiller LWT sensor control wiring. When chillers are con-figured to operate in series mode no additional chilled watertemperature sensor is required.The master chiller will monitor all external commands such asstart/stop, demand limiting, or set point select, and needs to bestarted in Master operating type. The commands are transmittedautomatically to the slave unit, which must operate in CCN (Net-work) mode. The slave chiller has no action in the master/slaveoperations; it will only verify that CCN communication with themaster chiller is correct. If the master chiller is turned off while themaster/slave function is active, then the slave chiller will bestopped. Under certain circumstances, the slave unit may be start-ed first to balance the run times of the two units. In the event of acommunication failure between the two units, each unit will returnto an autonomous operating mode until the fault is cleared. If themaster unit is stopped due to an alarm, the slave unit is authorizedto start and therefore the slave unit configurations should be veri-fied with desired set points.The CCN communication port for the Master and Slavechillers must be joined using a shielded cable in order to avoidcommunication issues.The master/slave linkage will not be allowed to operate if anyone of the slave chiller CTRL_PNT, DEM_LIM, LAG_LIM,or LCW_STPT variables has a force priority higher than acontrol force. In that case, the master/slave operations will notbe allowed or will be disabled.The control algorithm relies on several parameters that must befield configured for operation. Both chillers must be on thesame 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 arrangementmust be specified with the Chiller in Series variable (MainMenu Configuration Menu Master/Slave ConfigChiller in Series). The Master chiller must be programmedwith 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 ConfigurationMenu Master/Slave Config Lead Lag Select) determineswhich 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 timeincrement selected in the Lead/Lag Balance Delta configuration(Main Menu Configuration Menu Master/Slave Config Lead/Lag Balance Delta). If the run hour difference betweenthe master and the slave remains less than the Lead/ Lag BalanceDelta, the chiller designated as the lead will remain the leadchiller. The Lead/Lag changeover between the master and theslave 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, at12:00 a.m. If a lead chiller is not designated, the master chiller willalways be designated the lead chiller.The dual chiller control algorithm has the ability to delay thestart of the lag chiller in two ways. The Lead Pulldown Timeparameter (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 tostart an additional chiller. This time delay gives the lead chillera chance to remove the heat that the chilled water loop pickedup while inactive during an unoccupied period. The secondtime 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 leadchiller and the start of the lag chiller. This prevents enablingthe 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 UnitPump Control). If the difference between the common leavingwater 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 programmedwith the Lag Minimum Running Time configuration (MainMenu Configuration Menu Master/Slave ConfigLag Minimum Running Time). This parameter causes thecontrol to run the lag chiller for the programmed minimum ontime. 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 offwhile the chiller is off. This parameter is only active in ParallelChiller Operation.The lead chiller is started first and the lag chiller will be main-tained at zero percent capacity through master forcing the lagdemand limit value (LAG_LIM) to 0%. The lag water pumpwill be maintained off. When the lead chiller cannot be loadedanymore (because it is loaded at its full available capacity or atthe 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 waterpump will be turned on (if required by configuration) and thelag chiller will be allowed to start through the master chillerforcing the lag chiller demand limit value (LAG_LIM) to itsown demand limit value. To ensure that the lag chiller will beunloaded first in case of water load decrease, the lead chillerset 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 describedseparately below.DUAL CHILLER CONTROL FOR PARALLEL APPLICA-TIONSTo configure the master chiller for parallel applications, see Ta-ble 26. To configure the slave chiller for parallel applications,see Table 27.