Carrier 19XRV Start-up, Operation And Maintenance Instructions Manual

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

Contents

39If kilowatts is selected for the DEMAND LIMIT SOURCE,the MOTOR RATED LOAD KILOWATTS must beentered in the VFD_CONF screen.The TEMP PULLDOWN DEG/MIN may be viewed ormodified on the TEMP_CTL screen which is accessedfrom the EQUIPMENT SERVICE screen. PULLDOWNRAMP TYPE, DEMAND LIMIT SOURCE, and AMPSOR KW RAMP %/MIN may be viewed or modified on theRAMP_DEM screen.5.8 - Capacity override (Table 6)Capacity overrides can prevent some safety shutdownscaused by exceeding the motor amperage limit, low evapo-rator temperature safety limit, high motor temperaturesafety limit, and high condenser pressure limit. In all cases,there are two stages of compressor capacity controlapplied by guide vane operation:1. When the value of interest crosses the First Stage SetPoint into the Override Region, the guide vanes areprevented from opening further, and the status line onthe ICVC indicates the reason for the override. Normalcapacity control operation is restored when the valuecrosses back over the First Stage Set point, leaving theOverride Region. See Table 6.. When the value of interest is in the Override Regionand further crosses the Second Stage Set Point, theguide vanes are closed until the value meets theOverride Termination Condition. The PIC III controlsresume normal capacity control operation after theoverride termination condition has been satisfied. (Inthe case of high discharge superheat, there is anintermediate stage.)Whenever the motor current demand limit set point(ACTIVE DEMAND LIMIT) is reached, it activates acapacity override, again, with a -step process. Exceeding110% of the rated load amps for more than 30 seconds willinitiate a safety shutdown.The high compressor lift (surge prevention) set point willcause a capacity override as well. When the surge preventionset point is reached, the controller normally will onlyprevent the guide vanes from opening. If so equipped, thehot gas bypass valve will open instead of holding the vanes.The hot gas bypass will only open if the compressor is at100% speed. See the Surge Prevention Algorithm section,page 43.5.9 - High discharge temperature controlIf the COMP DISCHARGE TEMP increases above 71.1°C,the guide vanes are proportionally opened to increase gasflow through the compressor. If the LEAVING CHILLEDWATER temperature decreases .8 K below the control setpoint temperature, as a result of opening the guide vanes,the PIC III will bring the chiller into the recycle mode.5.10 - Oil sump temperature and pump controlThe oil sump temperature is regulated by the PIC III, withthe oil heater relay when the chiller is shut down.As part of the pre-start checks executed by the controls, theoil sump temperature (OIL SUMP TEMP) is compared tothe evaporator refrigerant temperature (EVAPORATORREFRIG TEMP) if the OIL SUMP TEMP is less than65.6°C. If the difference between these temperatures is7.8 K or less, the start-up will be delayed until either ofthese conditions is no longer true. Once this temperaturecriteria is satisfied, the start-up continues.The oil heater relay is energised whenever the chillercompressor is off and the oil sump temperature is less than60°C or the OIL SUMP TEMP is less than the EVAPREFRIG TEMP plus 9.4 K. The oil heater is turned offwhen the OIL SUMP TEMP is either:• more than 66.7°C, or• more than 61.1°C and more than the EVAP REFRIGTEMP plus 30.6 K.The oil heater is always off during start-up or when thecompressor is running.The oil pump is also energised during the time the oil isbeing heated (for 30 seconds at the end of every 30 minutes).The oil pump will not operate if the EVAPORATORPRESSURE is less than –34.5 kPa.5.11 - Oil coolerThe oil must be cooled when the compressor is running.This is accomplished through a small, plate-type heatexchanger (also called the oil cooler) located behind the oilpump. The heat exchanger uses liquid condenser refrigerantas the cooling liquid. Refrigerant thermostatic expansionvalves (TXVs) regulate refrigerant flow to control the oiltemperature entering the bearings. The bulbs for theexpansion valves are strapped to the oil supply line leavingthe heat exchanger, and the valves are set to maintain 43°C.NOTE: The TXVs are not adjustable. The oil sump tempe-rature may be lower during compressor operation.