Carrier AquaForce 30XV140 Controls, Start-up, Operation, Service And Troubleshooting Instructions

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

Contents

33DUAL CHILLER PUMP CONTROL FOR SERIESCHILLER APPLICATIONS — Pump control for serieschiller applications is controlled by the master chiller only.The control of the slave chiller is directed through com-mands emitted by the master chiller. The slave chiller has noaction in master/slave operations. The slave chiller only ver-ifies that CCN communication with the master chiller ispresent. See the Dual Chiller Sequence of Operation sectionon page 47. Figure 29 shows a typical pump arrangementfor dual chiller series applications.Ramp Loading — The Ramp Loading function limits therate of change of the leaving fluid temperature. The minimumcompressor speed is calculated based on saturated condensingtemperature and saturated suction temperature. To enable theRamp Loading sequence:Temperature Reset — The temperature reset functionwill determine the cooling control point. This control pointis the active set point adjusted with the current reset value:Control Point = Setpoint + ResetThe purpose of this reset value is to decrease the requiredcapacity if it is allowed by unit load operating conditions.When a non-zero temperature reset is applied, the chiller con-trols to the new control point instead of the set point. The typeof temperature reset is configured with the Cooling Reset Se-lect variable. Four types of temperature reset are available:Outdoor Air Temperature (OAT), Return Water Reset (DeltaT), 4-20mA control, and Space Temperature control:Under normal operation, the chiller will maintain a con-stant entering or leaving fluid temperature, based on theconfiguration, approximately equal to the chilled fluid setpoint. As the evaporator load varies, the evaporator fluidtemperature difference will change in proportion to the load.For example, if the chiller was selected for an entering toleaving water temperature difference of 10° F (5.5° C) atfull load, at 50% load the temperature difference would be5° F (2.2° C). See Fig. 30. Because the change in tempera-ture through the evaporator is a measure of the buildingload, the temperature difference reset is the average build-ing load. Usually the chiller size and fluid temperature setpoint are selected based on a full load condition. At partload, the fluid temperature set point may be lower than re-quired. When the fluid temperature is allowed to increase atpart load, the efficiency of the machine will increase. Thechiller can also be set for return water temperature control.See Fig. 31.Other indirect means of estimating building load andcontrolling temperature reset are also available and are dis-cussed below.To verify that reset is functioning correctly, subtract theCurrent Setpoint (Main Menu  General Parameters  Cur-rent Setpoint) from the Control Point (Main Menu  GeneralParameters  Control Point) to determine the degrees reset.DISPLAY NAME PATH VALUERamp LoadingEnableMain Menu Configuration Menu General ConfigurationYesCooling RampLoadingMain MenuSetpoint TableRange: 0.2 to 2.0° F/min(0.1 to 1.1° C/min)Default: 1.0° F/min(0.5 °C/min)DISPLAYNAME PATH VALUECooling ResetSelectMain Menu Configuration Menu Reset Configuration0 = None1 = OAT2 = Delta T3 = 4-20 mA Control4 = Space TempFig. 29 — Typical Series Master/Slave ChillersDedicated Primary Pumping, Constant Flow, Leaving Water ControlCONTROL BOXMASTERCHILLERLOADBYPASS LOOPFIELD WIRINGFIELD COMMUNICATION WIRINGNOTE: This is a simplified wiring diagram.Not all hydronic specialties are shown.MASTER PUMPISOLATIONVALVESCONTROL BOXSLAVECHILLER