Diffuser Control; Proportional Bands And Gain; Demand Limiting; Chiller Timers And Starts Counter - Carrier 19XRV Start-Up, Operation And Maintenance Instructions Manual

2 mA
(0%)
Full
4 mA
Open
(0.2%)
surge more likely
rotating stall
less likely
Full
Closed
25 % Load Point
approx.
4 mA*
(100%)
0 %
* Diffuser full Span mA.
Fig. 21 — Diffuser Control
Diffuser control output is enabled whenever the DIFFUSER
OPTION is enabled, whether the machine is running or not. As
shown in Fig. 21, 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.
PROPORTIONAL BANDS AND GAIN — Proportional band
is the rate at which capacity control (including guide vane
position and, if applicable, VFD speed) is adjusted in propor-
tion to how far the chilled water/brine temperature is from the
CONTROL POINT. Proportional gain determines how quickly
capacity control reacts to how quickly the temperature is
moving from the CONTROL POINT. The proportional bands
and gain may be viewed or modified from the SETUP2 screen,
which is accessed from the EQUIPMENT SERVICE table.
The Proportional Band — There are two response modes, one
for temperature response above the control point, the other for
the response below the control point.
The temperature response above the control point is called
the PROPORTIONAL INC BAND, and it can slow or quicken
capacity control response to chilled water/brine temperatures
above the CHILLED WATER DEADBAND. The PROPOR-
TIONAL INC BAND can be adjusted from a setting of 2 to 10;
the default setting is 6.5.
The response below the control point is called the PRO-
PORTIONAL DEC BAND, and it can slow or quicken the ca-
pacity control response to chilled water temperature below the
deadband plus the control point. The PROPORTIONAL DEC
BAND can be adjusted on the ICVC from a setting of 2 to 10.
The default setting is 6.0.
NOTE: Increasing either of these settings causes the capacity
control to respond more slowly than at a lower setting.
The PROPORTIONAL ECW GAIN can be adjusted on the
ICVC display for values of 1, 2, or 3; the default setting is 2.
Increase this setting to increase guide vane response to a
change in entering chilled water temperature.
DEMAND LIMITING — The PIC III controls provide a
feature for limiting AVERAGE LINE CURRENT or LINE
75 % Load Point
surge less likely
50 % Load Point
50 %
78 %
GUIDE VANE OPENING (%)
a19-1620
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 25, 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 47).
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
demand limiting based on PERCENT LINE KILOWATTS
(displayed in the MAINSTAT screen). LINE KILOWATTS is
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)
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
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 (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 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.
A DEMAND KILOWATTS monitoring feature is also
available. 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 SER-
VICE / EQUIPMENT SERVICE/RAMP_DEM screen.
CHILLER TIMERS AND STARTS COUNTER — The 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 oppor-
tunity, before the first startup with the new controller, is
provided 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.
38