Specifications

ManualsBrandsCarrier ManualsAir Compressor19XRV

the graph (default settings are shown) describe a line the algo-

rithm uses to determine the maximum lift of the compressor for

the particular maximum operating speed. When the actual dif-

ferential pressure between the cooler and condenser (delta P)

and the temperature difference between the entering and leav-

ing chilled water (delta T) are above the line on the graph (as

defined by the minimum and full load points), the algorithm

operates in Surge Prevention mode. This is determined when

the ACTIVE DELTA T is less than SURGE/HGBP DEAD-

BAND.

When in Surge Prevention mode, with a command to in-

crease capacity, the VFD speed will increase until maximum

VFD speed is reached. At VFD MAXIMUM SPEED, when Ca-

pacity still needs to increase, the IGV’s open. When in Surge

Prevention mode and with a command to decrease capacity

only the IGVs will close, the VFD speed will not decrease.

Surge Protection (VFD Chiller) — The PIC II mon-

itors surge, which results in a fluctuation on the compressor

motor amperage. Each time the fluctuation in amperage ex-

ceeds an operator-specified limit (SURGE DELTA % AMPS)

plus a load correction factor, both SURGE COUNTS are incre-

mented by one and the VFD will increase in speed provided

that it is not already operating at VFD MAXIMUM SPEED or

that the VFD TARGET SPEED is forced. If the VFD cannot

increase in speed because the VFD is already at maximum

speed of the target speed is forced then the SURGE PROTEC-

TION COUNTS are also incremented by one. If more than 4

SURGE PROTECTION COUNTS occur within an operator-

specified time (SURGE TIME PERIOD) and the ACTUAL

VFD SPEED is greater than 90% then the PIC II declares an

Excessive Compressor Surge Alarm (238) and the chiller is

shut down. If more than four SURGE PROTECTION

COUNTS occur within the SURGE TIME PERIOD and the

ACTUAL VFD SPEED is less than 90% then the chiller is shut

down on a Excessive Compressor Surge / Low Speed Alarm

(236). Both SURGE COUNTS and SURGE PROTECTION

COUNTS are decreased by one if no surges occur within the

SURGE TIME PERIOD.

On chillers with VFDs, if a SURGE COUNT is registered

and the ACTUAL VFD SPEED is less than the VFD MAXI-

MUM SPEED then the TARGET VFD SPEED will be in-

creased by the amount configured in the VFD INCREASE

STEP parameter. The VFD will not decrease in speed if

SURGE COUNTS is greater than zero.

The threshold at which a current fluctuation is interpreted as

a surge can be adjusted from the OPTIONS screen. The por-

tion of the surge threshold attributable to current fluctuations

can be changed by scrolling to the SURGE DELTA % AMPS

parameter and adjusting it with the INCREASE or DE-

CREASE softkeys. The default setting is 10 %. The SURGE

TIME PERIOD can be adjusted from the OPTIONS screen.

Scroll to the SURGE TIME PERIOD parameter and use the

INCREASE or DECREASE softkey to adjust the surge count

time interval. The default setting is 8 minutes.

SURGE PROTECTION COUNTS are displayed in the

COMPRESS screen. Both SURGE PROTECTION COUNTS

and SURGE COUNTS are displayed in the SURGPREV

screen.

VFD Start-Up Speed Control — Immediately accel-

erating to a high VFD speed improves the ability of the com-

pressor to compensate for some start-up environments that ex-

ceed condenser water design conditions. The 19XRV chillers

initially accelerate to high VFD speed and then gradually slow

the compressor, if possible, while adjusting the guide vane po-

sition until a stable operating point with improved chiller effi-

ciency is attained.

Following a start command, the PIC II controls internally

set the VFD TARGET SPEED to the smaller of the VFD

MAXIMUM SPEED or the VFD START SPEED. Provided

that the chiller has sufficient capacity, the VFD will continue to

run at the startup speed during Ramp Loading until the chilled

water temperature falls within the CHILLED WATER DEAD-

BAND surrounding the Setpoint. RAMP LOADING AC-

TIVE in the SURGPREV screen will indicate YES during

Ramp Loading. The GUIDE VANE DELTA will be equal to

zero when the chilled water temperature is in the CHILLED

WATER DEADBAND. The VFD speed will then be ramped

down at one half of the VFD GAIN rate until, surge conditions

are encountered, the VFD MINIMUM SPEED is reached, the

ACTUAL GUIDE VANE POS reaches the GUIDE VANE

TRAVEL LIMIT, or the TARGET VFD SPEED is forced.

VFD RAMPDOWN ACTIVE in the SURGPREV screen will

indicate YES during the rampdown process. The VFD speed

will be regulated by standard capacity control and surge pre-

vention algorithms at the conclusion of the rampdown process.

Head Pressure Reference Output (See

Fig. 27) —

The PIC II control outputs a 4 to 20 mA signal

for the configurable Delta P (CONDENSER PRESSURE mi-

nus EVAPORATOR PRESSURE) reference curve shown in

Fig. 27. An output is available on the ISM module [Terminal

J8-3 (+), J8-4 (–) labeled spare]. The DELTA P AT 100% (chill-

er at maximum load condition default at 50 psi [344 kPa]),

DELTA P AT 0% (chiller at minimum load condition default at

25 psi [172.4 kPa]) and MINIMUM OUTPUT points are con-

figurable in the EQUIPMENT SERVICE-OPTIONS table.

When configuring this output ensure that minimum require-

ments for oil pressure and proper condenser FLASC orifice

performance are maintained.

The output may be useful as a reference signal to control a

tower bypass valve, tower speed control, condenser pump

speed control, etc. Note that it is up to the site design engineer-

ing agent to integrate this analog output with any external sys-

tem device(s) to produce the desired effect. Carrier does not

make any claim that this output is directly usable to control any

specific piece of equipment (that is, without further control ele-

ments or signal conditioning), although it may be.

The head pressure reference output will be on whenever the

condenser pump is operating; it may also be manually operated

CONTROLS TEST. When the head pressure differential is less

than the value entered for

DELTA P AT 0%, the output will be

maintained at 4 mA. The output is 2 mA when the chiller is not

running.

Lead/Lag Control — The lead/lag control system auto-

matically starts and stops a lag or second chiller in a 2-chiller

water system. A third chiller can be added to the lead/lag

MINIMUM

REFERENCE

OUTPUT

DELTA P

AT 100%

DELTA P

AT 0%

DELTA P

0 mA 2 mA

4 mA

(0%)

20 mA

(100%)

4 T0 20 mA OUTPUT

Fig. 27 — Head Pressure Reference Output

(Minimum Set Above 4 mA)