20
set to around 30 Hz. The HGBP valve will deenergize once
speed exceeds HGBP Enable Below Speed plus Disable
Speed Deadband. A typical value for Disable Speed Dead-
band is 15 Hz.
NOTE: HGBP control based on compressor speed is the typical
configuration mode.
DEMAND LIMIT
The PIC6 controls provide a feature for limiting AVERAGE
LOAD CURRENT or MOTOR KILOWATTS by limiting capaci-
ty via VFD speed. The limit may be applied in two ways. The first
is called ACTIVE DEMAND LIMIT, which is equal to a BASE
DEMAND LIMIT value (set in the SETPOINT screen, default
value 100%). ACTIVE DEMAND LIMIT may also be forced to
be different from BASE DEMAND LIMIT by manually overrid-
ing (forcing) the value via a CCN network device. If the DE-
MAND LIMIT SOURCE exceeds the ACTIVE DEMAND LIM-
IT by 5% or less, capacity will be inhibited. If the DEMAND
LIMIT SOURCE exceeds the ACTIVE DEMAND LIMIT by
more than 5%, capacity will be decreased. See Fig. 37.
Fig. 37 — Demand Limit
In the General Configuration menu, the Demand Limit Source set
to 0 = Local makes Demand Limit follow the setting in Ramp
Loading Type; i.e., either load current or motor kW. A value be-
tween 20 and 100% can be entered for Circuit A Capacity Limit
and the controls will load to the selected setting.
If Demand Limit Source is selected to be 1=AnalogIO the
Demand Limit is controlled by a 4-20 mA input to 7TB-7,8
(AUTO_DEM). The Demand Limit at 20 mA is configured in the
Service Configuration Menu. See Fig. 38-39.
Fig. 38 — Service Configuration, Screen 1
Fig. 39 — Service Configuration, Screen 2
RUNNING TIMERS AND COUNTERS
The PIC6 control maintains several run-time clocks: Service Run-
time, Machine Operating Hours, and Compressor Hours. Machine
Operating Hours and Compressor Hours are typically the same
and indicates to total machine/compressor run hours, but they
could be different in the case of a compressor replacement. Ser-
vice Runtime is a 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 Compressor A Starts. All of these can be
viewed on the RUNTIME screen. Manual changes to SERVICE
ONTIME from the screen are permitted at any time. Runtime tim-
ers and counters can be set from Configuration MenuUpdate
Runtime; see Fig. 40. Factory Level Password is required.
Fig. 40 — Update Runtime
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. Time
Until Start can be viewed in the Status MenuUnit Status table.
They must expire before the chiller starts. If the timers have not
expired, the Unit Status is Timeout.
WATER PUMPS CONTROL (FREEZE PREVENTION)
Carrier must have direct or parallel control of the chiller water
pumps. Pump control connection must be either hardwire of con-
trolled via BMS commands that originates from chiller controller.
Pump control is critical for freeze protection and warranty may be
voided should freeze-up occur without proper control installation.
Evaporator Freeze Prevention
Evaporator freeze protection is in effect in all run statuses.
Alarm shutdown shall be tripped. If chiller is in recycle mode
then it shall transition to trip out.
If any of the CALC EVAP SAT TEMP, EVAP REFRIG LIQUID
TEMP, LCW or ECW is less than or equal to the EVAP REFRIG
TRIPPOINT plus 1°F (0.55°C), evap freeze flag shall be set to
true and the Evaporator Freeze Protection shall be activated
and remain on until all are greater than the EVAP REFRIG
TRIPPOINT plus 5°F (2.8°C).
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