Demand Limiting; Chiller Timers And Starts Counter; Occupancy Schedule - Carrier AquaEdge 19XR series Start-Up, Operation And Maintenance Instructions Manual

100%
Open
surge more likely
50 % Load Point
rotating stall
less likely
25 % Load Point
100%
Closed
0 % 25 %
GUIDE VANE POSITION (% OPEN)
* DIFFUSER FULL SPAN MA.
Fig. 25 — Diffuser Control
DEMAND LIMITING — The PIC II controls provide a fea-
ture for limiting AVERAGE LINE CURRENT or LINE
KILOWATTS (demand) by limiting capacity via guide vane
control. The limit applied is called ACTIVE DEMAND
LIMIT, which is equal to a BASE DEMAND LIMIT value
(set in the SETPOINTS Screen, page 34, default value 100%),
or that determined by AUTO DEMAND LIMIT INPUT (an
optional 4 to 20 mA input, described below). ACTIVE
DEMAND LIMIT may also be forced to be different from
BASE DEMAND LIMIT by manually overriding the value
(forcing) from the MAINSTAT screen or writing a value via a
CCN network device, or controlled by another chiller in Lead
Lag operation (see page 59).
The demand limit may be based on either line current or
kW, as indicated by DEMAND LIMIT SOURCE in the
EQUIPMENT SERVICE/RAMP_DEM table. The default is 0,
for demand limiting based on AVERAGE LINE CURRENT
(percent of RATED LINE AMPS, as displayed on the default
screen). Setting DEMAND LIMIT SOURCE to 1 makes de-
mand limiting based on PERCENT LINE KILOWATTS (dis-
played in the MAINSTAT screen). MOTOR PERCENT KILO-
WATTS is equal to (MOTOR KILOWATTS ÷MOTOR RATED
KILOWATTS ) ×100. MOTOR KILOWATTS is measured by
the ISM and the MOTOR RATED KILOWATTS value (100%
rated kW) is set on the RAMP_DEM screen.
If the DEMAND LIMIT SOURCE (average line current)
exceeds the ACTIVE DEMAND LIMIT by 5% or less, in-
creases in guide vane opening will be prevented. If the DE-
MAND LIMIT SOURCE (percent line current) exceeds the
ACTIVE DEMAND LIMIT by more than 5%, the guide vanes
will be forced to close. Also, as the DEMAND LIMIT
SOURCE approaches the ACTIVE DEMAND LIMIT from a
lower value, allowable capacity increases become increasingly
more limited, beginning when the DEMAND LIMIT
SOURCE is within the DEMAND LIMIT PROP BAND (con-
figurable in the RAMP_DEM table).
Demand Limit Control Option — The demand limit control
option (20 mA DEMAND LIMIT OPT) is externally con-
trolled by a 4 to 20 mA signal from an energy management
system (EMS). The option is set up on the RAMP_DEM
screen. When enabled, 4 mA will set ACTIVE DEMAND
LIMIT to 100% of the DEMAND LIMIT SOURCE (regard-
less of the value of BASE DEMAND LIMIT), and 20 mA will
set ACTIVE DEMAND LIMIT to the value configured as
"20MA DEMAND LIMIT OPT" in the RAMP_DEM table.
Wire the auto demand limit to terminals J5-1 (-) and J5-2
(+) on the CCM. In order to use a 1 to 5 vdc input instead of 4
to 20 mA, install a 25-ohm resistor in series with the + lead at
terminal J5-2. The associated dip switch should remain in the
2 mA
(0%)
4 mA
(0.2%)
75 % Load Point
surge less likely
approx.
20 mA
50 %
75 % 100 %
a19-1861
up (on) position despite the notation on the CCM board. See
Fig. 26.
A DEMAND KILOWATTS monitoring feature is also avail-
able. This feature provides a display of average demand
(power) in kilowatts (in the POWER screen). This value is
continuously updated and averaged over the preceding time
interval specified as DEMAND WATTS INTERVAL in the
SERVICE / EQUIPMENT SERVICE/RAMP_DEM screen.
Fig. 26 — Auto Demand Limit Wiring (1 to 5 vdc)
CHILLER TIMERS AND STARTS COUNTER — The
PIC II maintains two run time clocks: COMPRESSOR
ONTIME and SERVICE
ONTIME indicates the total lifetime compressor run hours.
SERVICE ONTIME is a resettable timer that can be used to
indicate the hours since the last service visit or any other event.
A separate counter tallies compressor starts as TOTAL COM-
PRESSOR STARTS. All of these can be viewed on the
MAINSTAT screen on the ICVC. Both ontime counters roll
over to 0 at 500,000 hours. Manual changes to SERVICE
ONTIME from the ICVC (or forced via the Service Tool) are
permitted at any time. If the controller is replaced, one oppor-
tunity, before the first start-up with the new controller, is pro-
vided to set COMPRESSOR ONTIME and TOTAL
COMPRESSOR STARTS to the last readings retained with the
prior controller. The SERVICE ONTIME timer can register up
to 32,767 hours before it rolls over to zero.
The chiller also maintains a start-to-start timer and a stop-
to-start timer. These timers limit how soon the chiller can be
started. START INHIBIT TIMER is displayed on the MAIN-
STAT screen. See the Start-Up/Shutdown/Recycle Sequence
section, page 64, for more information on this topic.
OCCUPANCY SCHEDULE — The chiller schedule, de-
scribed in the Time Schedule Operation section (page 27), de-
termines when the chiller can run. Each schedule consists of
from 1 to 8 occupied or unoccupied time periods, set by the op-
erator. The chiller can be started and run during an occupied
time period (when OCCUPIED? is set to YES on the
MAINSTAT display screen). It cannot be started or run during
an unoccupied time period (when OCCUPIED? is set to NO
on the MAINSTAT display screen). These time periods can be
set for each day of the week and for holidays. The day begins
with 0000 hours and ends with 2400 hours. The default setting
for OCCUPIED? is YES, unless an unoccupied time period is
in effect.
These schedules can be set up to follow a building's occu-
pancy schedule, or the chiller can be set so to run 100% of the
time, if the operator wishes. The schedules also can be by-
passed by forcing the CHILLER START/STOP parameter on
the MAINSTAT screen to START. For more information on
forced starts, see Local Start-Up, page 64.
47
a19-1885
ONTIME. COMPRESSOR