Chiller Timers And Starts Counter; Occupancy Schedule - Carrier 19XRV Start-Up, Operation And Maintenance Instructions Manual

5.1.6 - Demand limiting
The PIC III controls provide a feature for limiting AVE-
RAGE 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 0, default value 100%), or that determined
by AUTO DEMAND LIMIT INPUT (an optional 4 to 0
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 44).
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,
increases in guide vane opening will be prevented. If the
DEMAND 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 (configurable in the RAMP_DEM
table).
5.1.7 - Demand limit control option
The demand limit control option (0 mA DEMAND LIMIT
OPT) is externally controlled by a 4 to 0 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 0 mA will set ACTIVE
DEMAND LIMIT to the value configured as "0MA
DEMAND LIMIT OPT" in the RAMP_DEM table.
Wire the auto demand limit input to terminals J5-1 (–) and
J5- (+) on the CCM. In order to use a 1 to 5 V d.c. input
instead of 4 to 0 mA, install a 5-ohm resistor in series
with the + lead at terminal J5-.
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 SERVICE / EQUIPMENT SERVICE/RAMP_DEM
screen.

5.2 - 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 opportunity, 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 3,767 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
MAINSTAT screen. See the Start-Up/Shutdown/Recycle
Sequence section, page 51, for more information on this
topic.

5.3 - Occupancy schedule

The chiller schedule, described in the Time Schedule
Operation section (page 19), determines when the chiller
can run. Each schedule consists of from 1 to 8 occupied or
unoccupied time periods, set by the operator. 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 00.00 hours and ends with 4.00 hours. The
default setting for OCCUPIED? is YES, unless an unoccu-
pied 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
bypassed by forcing the CHILLER START/STOP parameter
on the MAINSTAT screen to START. For more information
on forced starts, see Local start-up, page 51.
The schedules also can be overridden to keep the chiller in
an occupied state for up to 4 hours, on a one time basis.
See the Time Schedule Operation section, page 19.
Fig. 8 shows a schedule for a typical office building with a
3-hour, off-peak, cool-down period from midnight to 3 a.m.,
following a weekend shutdown. Holiday periods are in an
unoccupied state 4 hours per day. The building operates
Monday through Friday, 7:00 a.m. to 6:00 p.m., and Satur-
days from 6:00 a.m. to 1:00 p.m. This schedule also includes
the Monday midnight to 3:00 a.m. weekend cool-down
schedule.
35