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

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Carrier 19XRV Start-up, Operation And Maintenance Instructions Manual Manual pdf 34 page image

PIC III System FunctionsIMPORTANT: Words not Du't of ptu'agraph headings andprinted in all capit_d letters can be viewed on the [CVC(e.g., LOCAL, CCN, RUNNING ALARM, etc.). Wordsprinted both in _dl capit_d letters and it_dics can also beviewed on the ICVC and tu'e parameters (CONTROLMODE, TARGET GUIDE VANE POS, etc.) with associatedv_dues (e.g., modes, temperatures, pressures, percentages,on, off. enable, disable, etc.). Words printed in _dlcapital let-ters and in a box represent sollkeys on the ICVC (e.g.,and _ ). See Table 4 for exmnples of the typeof information that can appegu on the ICVC screens. Figures14-20 give an overview of ICVC operations and menus.CAPACITY CONTROL -- Generally the chiller adjusts ca-pacity in response to deviation of leaving or entering chilled wa-ter temperature from control point. CONTROL POINT is basedon the configured SETPOINT (in the SETPOINT screen: LCWSET POINT or ECW SET POINT or ICE BUILD SETPOINT), and CONTROL POINT is equal to this SETPOINTplus any active chilled water reset value. A reset v_due mayoriginate from any of the three chilled water/brine reset optionsconfigured in the ICVC Service/Equipment Service/TEMP CTL screen (see page 42) or from a CCN device. Thedefault reset v_due is 0 ° E CONTROL POINT may be viewedor manually overridden from the MAINSTAT screen.Minor adjustments to the rate of capacity adjustment can bemade by changing PROPORTIONAL INC (Increase) BAND,PROPORTIONAL DEC (Decrease) BAND, and PROPOR-TIONAL ECW (Entering Chilled Water) GAIN in the Service/Equipment Service/SETUP2 screen. Increasing the PROPOR-TIONAL [NC BAND or PROPORTIONAL DEC BAND, ordecreasing PROPORTIONAL ECW GAIN will reduce theamplitude of the capacity control response (within limits). Seealso Proportional Bands and Gain on page 35.Factors and variables used in the capacity control determi-nation are displayed in the Service/Control Algorithln Status/Capacity screen and in the Status/COMPR screen. Viewing thisdata will aid in troubleshooting and understanding currentoperation.Variable Speed (VFD) Application -- The PIC III controlsthe machine capacity by modulating both motor speed andinlet guide vanes in response to chilled water temperature devia-tion from the CONTROL POINT (see above). During operationwhen the CONTROL POINT is not met within 1/3 the width ofthe CHILLED WATER DEAD)BAND, the controller will cal-culate a GUIDE VANE DELTA which will effect a percentagechange to either the guide vane position or TARGET VFDSPEED. Factol.s considered in the capacity control algorithln in-clude: (1) the sign and magnitude of GUIDE VANE DELTA(based on deviation from CONTROL POINT adjusted for theerror trends and CHILLED WATER DEAl)BAND), (2) AC-TUAL GUIDE VANE POSITION, (3) ACTUAL VFDSPEED, and (4) surge prevention mode. Generally the control-ler will maintain the highest inlet guide vane setting at the low-est speed to maximize efficiency while avoiding surge.First the c',_culation of GUIDE VANE DELTA is performed.If GUIDE VANE DELTA is positive, the response will be anIGV or VFD position increase (within limits). If GUIDE VANEDELTA is negative, the response will be gm IGV or VFD posi-tion decrease (within limits). Next, the surge prevention mode isdetemfined based on location of the present operating point onthe CHILLED WATER DELTA T/ACTIVE DELTA P map rel-ative the configured stage prevention line. This mode will eitherbe Norm_d or Surge Prevention. The table below indicates whichoutput is modulated that. When the Ih.st output roaches its limit(ACTUAL GUIDE VANE position roaches maximum), the sec-ond output is modulated. See Table 5.Table 5 -- Guide Vane Delta ModesNORMAL SURGEGUIDE VANE CONTROL PREVENTIONDELTA MODE MODEIGV VFD IGV VFDIncreaseonly if VFDspeed =From +0,2 to Increase Increase max and if Increase+2.0 1st when IGV hot gas 1st= max bypass ispresentand openDecreaseFrom -0.2 to when VFD Decrease Decrease ---2.0 speed = 1strninNormal Control mode occurs when ACTIVE DELTA T >SURGE/HGBP DELTA T_Surge Prevention Mode occurs when ACTIVE DELTA T< SURGE/HGBP DELTA T_The VFD GAIN ptuameter allows for additional adjustmentof the VFD response. Increasing VFD GAIN will increase therate of speed change.Generally for the case of line voltage equaling motor volt-age (460 volts), VFD output 0notor) current is a few percenthigher than line current at full speed (60 Hz). As drive speedsdecrease fiom maximum, drive output voltage decreaseslinedy with output frequency, and motor current continues toincrease relative to line current.The TARGET VFD SPEED, ACTUAL VFD SPEED and theVFD GAIN can be viewed and modified in the CAPACITYdisplay screen. The TARGET VFD SPEED can be manuallyoverridden by the operator fi'om the COMPRESS screen. TheVFD MINIMUM SPEED, VFD MAXIMUM SPEED, VFDGAIN and VFD INCREASE STEP can be selected and modi-fied in the SETUP2 display screen. TARGET and ACTUALVFD SPEED can be viewed in the COMPRESS screen.ECW CONTROL OPTION -- If this option is enabled, thePIC III uses the ENTERING CHILLED WATER temperature tomodulate the vanes instead of the LEAVING CHILLEDWATER temperature. The ECW CONTROL OPTION may beviewed on the TEMP_CTL screen, which is accessed fiom theEQUIPMENT SERVICE screen.CONTROL POINT DEAD)BAND-- This is the tolerancerange on the chilled water/brine temperature control point. If thewater temperature goes outside the CHILLED WATER DEAD-BAND, the PIC III opens or closes the guide vanes until the tem-perature is within tolerance. The PIC III may be configured witha 0.5 to 2 F (0.3 to 1.1 C) deadband. CHILLED WATER DEAD-BAND may be viewed or modified on the SETUPI screen,which is accessed from the EQUIPMENT SERVICE table.For example, a 1° F (0.6 ° C) deadband setting controls thewater temperature within _+0.5° F (0.3 ° C) of the control point.This may cause fiequent guide vane movement if the chilledwater load fluctuates frequently. A value of 1° F (0.6 ° C) is thedefault setting.DIFFUSER CONTROL--On all units with Frmne 5 com-pmssol.s and those Frmne 4 compressors with the variable (splitring) dilluser option, the PIC III adjusts the difluser actuatorposition (DIFFUSER ACTUATOR on the COMPRESS screen)based on the ACTUAL GUIDE VANE POSITION. This isdone in accordance with a compressor build-specific "schedule"entered in the SETUP2 screen. The schedule consists of guidewme and diffuser positions for three points (designated as the25%, 50%, and 75% Load Points). In order for the schedule tobe valid, the guide vane values must be ascending and the dif-fuser values must be descending for the three points. Diflhseractuator output is controlled by a 4 to 20 mA output from CCMterminals J8-3(+) and J8-4(-). Figure shows the relationshipbetween diffuser-related pguameters for a typic_d build. SeeFig. 21.34