Diffuser Control; Demand Limiting; Chiller Timers And Starts Counter - Carrier AquaEdge 19XRV series Operation, Maintenance And Installation Manual

DIFFUSER CONTROL — On all units with Frame 5 com-
pressors and those Frame 4 compressors with the variable (split
ring) diffuser option, the PIC III adjusts the diffuser actuator
position (DIFFUSER ACTUATOR on the COMPRESS screen)
based on the ACTUAL GUIDE VANE POS. This is done in
accordance with a compressor build-specific "schedule" entered
in the SETUP2 screen. The schedule consists of guide vane and
diffuser positions for three points (designated as the 25%, 50%,
and 75% Load Points). In order for the schedule to be valid, the
guide vane values must be ascending and the diffuser values
must be descending for the three points. Diffuser actuator output
is controlled by a 4 to 20 mA output from CCM terminals J8-
3(+) and J8-4(–). Figure 26 shows the relationship between dif-
fuser-related parameters for a typical build.
2 mA
(0%)
Full
4 mA
Open
(0.2%)
surge more likely
rotating stall
less likely
Full
Closed
25 % Load Point
approx.
20 mA*
(100%)
0 %
* Diffuser full Span mA.
Fig. 26 — Diffuser Control
Diffuser control output is enabled whenever the DIFFUSER
OPTION is enabled, whether the machine is running or not. As
shown in Fig. 26, 0% output corresponds to a full open diffuser.
The minimum closed position (25% Load Point value) will be
at less than 100% for most diffusers (depending upon the
model). This coordinated guide vane-diffuser operation may be
tested in the Control Test selection "IGV & SRD Actuator."
Note that the diffuser actuator should NOT be forced to a great-
er percent than the configured 25% Load Point (maximum)
value. The diffuser opening can be incremented from fully open
to completely closed. A 0% setting is fully open; a 100% setting
is completely closed. To obtain the proper settings for Diffuser
Control, contact a Carrier Engineering representative.
DEMAND LIMITING — The PIC III controls provide a
feature 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 29, 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 56).
The demand limit may be based on either line current or kW,
as indicated by DEMAND LIMIT SOURCE in the EQUIP-
MENT SERVICE/RAMP_DEM table. The default is 0, for
demand limiting based on AVERAGE LINE CURRENT (per-
cent of RATED LINE AMPS, as displayed on the default
screen). Setting DEMAND LIMIT SOURCE to 1 makes
demand limiting based on PERCENT LINE KILOWATTS (dis-
played in the MAINSTAT screen). LINE KILOWATTS is
75 % Load Point
surge less likely
50 % Load Point
50 %
78 %
GUIDE VANE OPENING (%)
a19-1620
measured by the VFD, and the MOTOR RATED LOAD kW
value (100% rated kW) is set in the VFD_CONF table.
If the DEMAND LIMIT SOURCE (percent line current) ex-
ceeds the ACTIVE DEMAND LIMIT by 5% or less, increases
in guide vane opening will be prevented. If the DEMAND LIM-
IT SOURCE (percent line current) exceeds the ACTIVE DE-
MAND 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, begin-
ning when the DEMAND LIMIT SOURCE is within the DE-
MAND LIMIT PROP
RAMP_DEM table).
Demand Limit Control Option — The demand limit control
option (20 mA DEMAND LIMIT OPT) is externally controlled
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 (regardless of the value of
BASE DEMAND LIMIT), and 20 mA will set ACTIVE DE-
MAND LIMIT to the value configured as 20 mA DEMAND
LIMIT OPT in the RAMP_DEM table.
Wire the auto demand limit input 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. See Fig. 27.
Fig. 27 — Auto Demand Limit Wiring (1 to 5 vdc)
A DEMAND KILOWATTS monitoring feature is also avail-
able. This feature provides a display of average demand (pow-
er) in kilowatts (in the POWER screen). This value is contin-
uously updated and averaged over the preceding time interval
specified as DEMAND WATTS INTERVAL in the SERVICE/
EQUIPMENT SERVICE/RAMP_DEM screen.
CHILLER TIMERS AND STARTS COUNTER —
PIC III maintains two run time clocks: COMPRESSOR
ONTIME and SERVICE ONTIME. COMPRESSOR 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 COMPRESSOR
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
are permitted at any time. If the controller is replaced, one
opportunity, before the first start-up with the new controller, is
provided to set COMPRESSOR ONTIME and TOTAL COM-
PRESSOR 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
46
BAND (configurable in
a19-1885
the
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