Carrier 19XL PIC System Functions

PIC System Functions

NOTE:Throughout this manual, words printed in capital let-

ters and italics represent values that may be viewed on the

LID. SeeTable 2 for examples of LID screens. Point names

are listed in the Description column. An overview of LID

operation and menus is given in Fig. 13-19.

CAPACITY CONTROL — The PIC controls the chiller

capacity by modulating the inlet guide vanes in response to

chilled water temperature changes away from the CON-

TROL POINT.The CONTROL POINT may be changed by

a CCN network device, or is determined by the PIC adding

any active chilled water reset to the ECW (Entering Chilled

Water)SET POINT or LCW SET POINT. The PIC uses the

PROPORTIONALINC (Increase) BAND, PROPORTIONAL

DEC(Decrease) BAND, and the PROPORTIONAL ECW GAIN

todetermine how fast or slow to respond. CONTROL POINT

may be viewed/overridden on the Status table, Status01

selection.

ENTERING CHILLED WATERCONTROL — If this op-

tionis enabled, the PIC uses ENTERING CHILLED WATER

temperature to modulate the vanes instead of LEAV-

INGCHILLED WATER temperature. ENTERING CHILLED

WATERcontrol option may be viewed/modiﬁed on the Equip-

ment Conﬁguration table, Conﬁg table.

DEADBAND — This is the tolerance on the chilled water/

brine temperature CONTROL POINT. If the water temper-

aturegoes outside of the DEADBAND, the PIC opens or closes

the guide vanes in response until it is within tolerance. The

PICmay be conﬁgured with a 0.5 to 2 F (0.3 to 1.1 C) dead-

band.DEADBAND may be viewed or modiﬁed on the Equip-

ment Service1 table.

For example, a 1° F (0.6° C) deadband setting controls

the water temperature within ±0.5° F (0.3° C) of the con-

trol point.This may cause frequent guide vane movement if

the chilled water load ﬂuctuates frequently. A value of

1° F (0.6° C) is the default setting.

PROPORTIONALBANDSAND GAIN — Proportional band

is the rate at which the guide vane position is corrected in

proportion to how far the chilled water/brine temperature is

from the control point. Proportional gain determines how

quickly the guide vanes react to how quickly the tempera-

ture is moving from CONTROL POINT.

The proportional bandcan be viewed/modiﬁed on the LID.

There are two response modes, one for temperature re-

sponseabove the control point, the other for response below

the control point.

Theﬁrst type is called PROPORTIONAL INC BAND, and

it can slow or quicken vane response to chilled water/

brine temperature above DEADBAND. It can be adjusted

from a setting of 2 to 10; the default setting is 6.5. PRO-

PORTIONAL DEC BAND can slow or quicken vane re-

sponseto chilled water temperature below deadband plus control

point.It can be adjusted on the LID from a setting of 2 to 10,

and the default setting is 6.0. Increasing either of these set-

tings will cause the vanes to respond slower than at a lower

setting.

ThePROPORTIONAL ECW GAIN can be adjusted at the LID

display from a setting of 1.0 to 3.0, with a default setting of

2.0. Increase this setting to increase guide vane response to

a change in entering chilled water temperature. The propor-

tionalbands and gain may be viewed/modiﬁed on the Equip-

ment Service3 table.

DEMAND LIMITING — The PIC will respond to the

ACTIVE DEMAND LIMIT set point by limiting the open-

ing of the guide vanes. It will compare the set point

to either COMPRESSOR MOTOR LOAD or COMPRES-

SOR MOTOR CURRENT (percentage), depending on how

the control is conﬁgured for the DEMAND LIMIT SOURCE

which is accessed on the SERVICE1table. The default set-

ting is current limiting.

CHILLERTIMERS — The PIC maintains 2 runtime clocks,

known as COMPRESSOR ONTIME and SERVICE ON-

TIME.COMPRESSOR ONTIME indicates the total life-

time compressor run hours. This timer can register up

to 500,000 hours before the clock turns back to zero. The

SERVICE ONTIME is a resettable timer that can be used to

indicate the hours since the last service visit or any other

reason. The time can be changed through the LID to

whatever value is desired. This timer can register up to

32,767 hours before it rolls over to zero.

Thechiller also maintains a start-to-start timer and a stop-

to-starttimer. These timers limit how soon the chiller can be

started. See the Start-Up/Shutdown/Recycle Sequence sec-

tion, page 39, for operational information.

OCCUPANCYSCHEDULE— This schedule determines when

the chiller is either occupied or unoccupied.

Eachschedule consists of from one to 8 occupied/unoccupied

time periods, set by the operator.These time periods can be

enabled to be in effect, or not in effect,on each day of the

week and for holidays.The day begins with 0000 hours and

ends with 2400 hours. The chiller is in OCCUPIED mode

unless an unoccupied time period is in effect.

Thechiller will shut down when the schedule goes to UN-

OCCUPIED. These schedules can be set up to follow the

buildingschedule or to be 100% OCCUPIED if the operator

wishes. The schedules also can be bypassed by forcing the

Start/Stop command on the PIC Status screen to start. The

schedules also can be overridden to keep the unit in an OC-

CUPIED mode for up to 4 hours, on a one-time basis.

Figure 18 shows a schedule for a typical officebuilding

time schedule, with a 3-hour, off-peak cool down period

from midnight to 3 a.m., following a weekend shutdown.

Example: Holiday periods are unoccupied 24 hours per day.

The building operates Monday through Friday,7:00 a.m. to

6:00 p.m., with a Saturday schedule of 6:00 a.m. to

1:00 p.m., and includes the Monday midnight to 3:00 a.m.

weekend cool-down schedule.

NOTE: This schedule is for illustration only,and is not in-

tended to be a recommended schedule for chiller operation.

PSIOSoftware Version 08 and Lower — Whenever the chiller

is in the LOCAL mode, the chiller will start when the

OccupancySchedule 01 indicates OCCUPIED. When in the

CCN mode, Occupancy Schedule 02 is used.

PSIO Software Version09 and Higher — The Local Time

Schedule is still the Occupancy Schedule 01. The Ice Build

Time Schedule is Schedule 02 and the CCN Default Time

Schedule is Schedule 03. The CCN schedule number is de-

ﬁned on the Conﬁg table in the Equipment Conﬁguration

table on page 23. The schedule number can change to any

value from 03 to 99. If this schedule number is changed on

the Conﬁg table, the operator must use the Attach to Net-

workDevice table to upload the new number into the Sched-

ule screen. See Fig. 17.