Carrier AquaEdge 19XR series Start-up, Operation And Maintenance Instructions Manual

Also see for AquaEdge 19XR series: Installation instructions Start-up, operation and maintenance instructions

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Carrier AquaEdge 19XR series Start-up, Operation And Maintenance Instructions Manual Manual pdf 52 page image

52Ramp Loading — The ramp loading control slows downthe rate at which the compressor loads up. This control can pre-vent the compressor from loading up during the short period oftime when the chiller is started and the chilled water loop has tobe brought down to CONTROL POINT. This helps reduceelectrical demand charges by slowly bringing the chilled waterto CONTROL POINT. The total power draw during this periodremains almost unchanged.There are two methods of ramp loading with the PIC II.Ramp loading can be based on chilled water temperature or onmotor load. Either method is selected from the RAMP__DEMscreen.1. Temperature ramp loading (TEMP PULLDOWN RAMP)limits the degrees per minute rate at which either leavingchilled water or entering chilled water temperature de-creases. This rate is configured by the operator on theTEMP_CTL screen. The lowest temperature ramp load-ing rate will also be used if chiller power has been off for3 hours or more (even if the motor ramp load is selectedas the ramp loading method).NOTE: If chiller control power has been off for 3hours or more, the next start-up (only) will follow theminimum configurable temperature ramp rate regard-less of the ramp loading method and rate which areconfigured in the screens. This is used to maximize oilreclaim during start-up.2. Motor load ramp loading (MOTOR LOAD RAMP%/MIN) limits the percent per minute rate at which the com-pressor motor current or compressor motor load increas-es. The LOAD PULLDOWN rate is configured by theoperator on the RAMP_DEM screen in amps or kilo-watts. The point name is MOTOR LOAD RAMP%/MIN.If kilowatts is selected for the DEMAND LIMIT SOURCE,the MOTOR RATED KILOWATTS must be entered on theRAMP_DEM screen (information found on the chiller Requi-sition form).The TEMP PULLDOWN DEG/MIN may be viewed ormodified on the TEMP_CTL screen which is accessed fromthe EQUIPMENT SERVICE screen. PULLDOWN RAMPTYPE, DEMAND LIMIT SOURCE, and MOTOR LOADRAMP %/MIN may be viewed or modified on theRAMP_DEM screen.Rampdown — The Rampdown control applies to VFDequipped chillers. At machine start-up the VFD speed is set to“Start Speed” which is the lower of VFD MAXIMUM SPEEDor the configured value of VFD START SPEED. VFD STARTSPEED is configured on the SETUP2 screen. After RampLoading is complete the control begins to reduce the VFDspeed. Speed reduction continues until the leaving water tem-perature is within the control point dead band and any condi-tion is reached that would require the VFD speed to hold or in-crease. The chiller is then out of Rampdown and running innormal capacity control.Capacity Override (Table 7) — Capacity overrides canprevent some safety shutdowns caused by exceeding the motoramperage limit, refrigerant low temperature safety limit, motorhigh temperature safety limit, and condenser high pressurelimit. In all cases there are 2 stages of compressor vane control.1. When the value of interest crosses the First Stage SetPoint into the Override Region, the guide vanes are pre-vented from opening further, and the status line on theICVC indicates the reason for the override. Normal ca-pacity control operation is restored when the value cross-es back over the First Stage Set Point, leaving the Over-ride Region. See Table 7.2. When the value of interest is in the Override Region andfurther crosses the Second Stage Set Point, the guidevanes are closed until the value meets the Override Ter-mination Condition. The PIC II controls resume normalcapacity control operation after the override terminationcondition has been satisfied. (In the case of high dis-charge superheat, there is an intermediate stage.)Whenever the motor current demand limit set point(ACTIVE DEMAND LIMIT) is reached, it activates a capacityoverride, again, with a 2-step process. Exceeding 110% of therated load amps for more than 30 seconds will initiate a safetyshutdown.The compressor high lift (surge prevention) set point willcause a capacity override as well. When the surge preventionset point is reached, the controller normally will only preventthe guide vanes from opening. If so equipped, the hot gas by-pass valve will open instead of holding the vanes. See theSurge Prevention section, page 56.If the chiller is VFD-equipped, the guide vanes will be al-lowed to open during surge prevention if the VFD is at 100%speed or forced and the chiller is in Ramp Loading or in Ramp-down. Opening the vanes will assist in loading the compressorto bring it out of the surge prevention range.High Discharge Temperature Control — If thedischarge temperature increases above 160 F (71.1 C), theguide vanes are proportionally opened to increase gas flowthrough the compressor. If the leaving chilled water tempera-ture is then brought 5 F (2.8 C) below the control set pointtemperature, the PIC II will bring the chiller into the recyclemode.Compressor Bearing Temperature — The thrustbearing temperature (MTRB) is a calculated value which is thetemperature of the oil leaving the bearing plus an internal incre-ment calculated with the THRUST BRG RESET FACTOR. TheComp Thrust Bearing Reset is calculated using the rate ofchange of the oil leaving the bearing. If the oil temperature isstable the COMP THRUST BRG TEMP equals the COMPTHRUST LVG OIL TEMP. As the oil temperature rises, theCOMP THRUST BRG RESET is calculated to account for anylag between actual bearing temperature and the temperature ofthe leaving oil.In the SETUP1 screen an adjustment called the THRUSTBRG RESET FACTOR is an adjustment to the COMP THRUSTBRG TEMP calculation. The default value is 1.4 and will nor-mally be left at that value unless other wise advised by CarrierService Engineering.Oil Sump Temperature and Pump Con-trol — The oil sump temperature control is regulated by thePIC II, which uses the oil heater relay when the chiller is shutdown.As part of the pre-start checks executed by the controls, theoil sump temperature (OIL SUMP TEMP) is compared to thecooler refrigerant temperature (EVAPORATOR REFRIGTEMP). If the oil temperature is less than 150 F (65.6 C) andthe difference between these 2 temperatures is 50 F (27.8 C) orless, the start-up will be delayed until either of these conditionsis no longer true. Once this temperature is confirmed, the start-up continues.The oil heater relay is energized whenever the chiller com-pressor is off and the oil sump temperature is less than 140 F(60.0 C) or the oil sump temperature is less than the evaporatorrefrigerant temperature plus 53 F (11.7 C). The oil heater isturned off when the oil sump temperature is either• more than 152 F (66.7 C), or• more than 142 F (61.1 C) and more than the evaporatorrefrigerant temperature plus 55 F (12.8 C).