Specifications

41
A No Flow determination is made on the evaporator side if
(1) the EVAP SATURATION TEMP reads lower than 1° F (0.6°
C) below the EVAP REFRIG TRIPPOINT, or (2) EVAP RE-
FRIG TEMP (determined from the Evaporator Pressure sen-
sor) is less than the EVAP REFRIG TRIPPOINT and the
EVAPORATOR APPROACH exceeds the configured EVAP
APPROACH ALERT threshold. On the condenser side, a No
Flow determination is also made if the CONDENSER AP-
PROACH exceeds the configured COND APPROACH ALERT
threshold and either (1) CONDENSER PRESSURE exceeds
165 psig (1139 kPa) or (2) CONDENSER PRESSURE exceeds
the configured COND PRESS OVERRIDE threshold by more
than 5 psi (34.5 kPa). In addition, if the water side differential
pressure measurement option is enabled, a differential below
the configured EVAP or COND FLOW DELTA P CUTOUT
value is sufficient to establish No Flow in either heat
exchanger.
If No Flow (for either cooler or condenser) has been deter-
mined, and subsequently conditions change such that neither
conditions for Flow nor No Flow are all satisfied, the determi-
nation will remain No Flow.
In the standard ICVC setup, waterside differential pressure
indication is disabled by default. The displays for CHILLED
WATER DELTA P and CONDENSER WATER DELTA P in the
HEAT_EX screen will show “*****”. In order to enable the
option and display a value, change FLOW DELTA P DISPLAY
to ENABLE in the SETUP1 screen. Pairs of pressure transduc-
ers may be connected to the CCM at terminals J3 13-24 in
place of the standard resistors and jumpers to determine water-
side pressure differentials as in the standard ICVC configura-
tion. (NOTE: If the FLOW DELTA P DISPLAY is enabled, but
the standard CCM connection is retained, a differential value of
approximately 28.5 psi (197 kPa) will always be displayed.)
If waterside differential pressure transducers are used, flow
is detected from differential pressure between sensors (pressure
transducers) located in water inlet and outlet nozzles, for each
heat exchanger. The thresholds for flow determination (EVAP
FLOW DELTA P CUTOUT, COND FLOW DELTA P CUT-
OUT) are configured in the SETUP1 screen. If the measured
differential is less than the corresponding cutout value for 5
seconds, the determination is that flow is absent. If no flow is
detected after WATER FLOW VERIFY TIME (configured in
the SETUP1 screen) after the pump is commanded to start by
the PIC, a shutdown will result, and the corresponding loss-of-
flow alarm (alarm state 229 or 230) will be declared. If the
measured differential exceeds the FLOW DELTA P cutout val-
ue, flow is considered to be present.
Alternatively, normally open flow switches may be used for
flow indication. In this case, install an evaporator side flow
switch in parallel with a 4.3k ohm resistor between CCM ter-
minals J3 17-18, replacing the jumper. For a condenser side
flow switch do the same between CCM terminals J3 23-24. If
this type of flow switch circuit is used, it is important to per-
form a zero point calibration (with the flow switch open).
CAPACITY CONTROL — Generally the chiller adjusts ca-
pacity in response to deviation of leaving or entering chilled
water temperature from its control point. CONTROL POINT is
based on the configured SETPOINT (in the SETPOINT screen:
LCW SETPOINT or ECW SETPOINT or ICE BUILD SET-
POINT), and CONTROL POINT is equal to this SETPOINT
plus any active chilled water reset value. A reset value may
originate from any of the three chilled water/brine reset options
configured in the ICVC SERVICE/EQUIPMENT SERVICE/
TEMP_CTL screen (see page 53) or from a CCN device. The
default reset value is 0
o
F so that if no reset function is config-
ured the CONTROL POINT will equal the SETPOINT. CON-
TROL POINT may be viewed or manually overridden from the
MAINSTAT screen.
Minor adjustments to the rate of capacity adjustment can be
made by changing PROPORTIONAL INC (Increase) BAND,
PROPORTIONAL DEC (Decrease) BAND, and PROPOR-
TIONAL ECW (Entering Chilled Water), GAIN in the SER-
VICE/EQUIPMENT SERVICE/SETUP2 screen. Increasing
the PROPORTIONAL INC BAND or PROPORTIONAL
DEC BAND, or decreasing PROPORTIONAL ECW GAIN
will reduce the rate of the capacity control response (within
limits). See also "PROPORTIONAL BANDS" on page 42.
Parameters used in the capacity control determination are
displayed in the SERVICE/CONTROL ALGORITHM STA-
TUS/CAPACITY screen and in the STATUS /COMPR screen.
Viewing this data will aid in troubleshooting and understanding
current operation.
Maximum guide vane travel is configurable as a percent of
full travel in the SETUP2 screen. Note that the default maxi-
mum is 80%. Note the guide vane position at design condi-
tions. Set the maximum travel approximately 5% higher. This
will prevent the vanes from opening wide during temporary
overload conditions. This will keep the vanes close to the actu-
al working load position and they should be able to resume
control successfully when the load drops.
In addition to its response to control point error and resets,
guide vane action and response rates are affected by guide vane
position, capacity overrides (see page 49), proportional bands
and gain (see page 42), and VFD speed (see below). Parame-
ters affecting guide vane action are displayed in the CAPACI-
TY screen of the SERVICE/CONTROL ALGORITHM STA-
TUS menu.
FIXED SPEED APPLICATIONS — For fixed speed appli-
cations, capacity is adjusted solely by movement of the inlet
guide vanes. Note that when operating in the surge prevention
region, the guide vanes cannot open further and may be forced
to close. (See SURGE PREVENTION.)
VARIABLE SPEED (VFD) APPLICATIONS — The PIC II
controls the machine capacity by modulating both motor speed
and inlet guide vanes in response to changes in load. During
operation, when the WATER TEMPERATURE is further from
the CONTROL POINT than 1/3 the value of the CHILLED
WATER DEADBAND, the controller will calculate a GUIDE
VANE DELTA which will cause a change to either the guide
vane position or VFD target speed. Factors considered in the
capacity control algorithm include: (1) the sign and magnitude
of GUIDE VANE DELTA (based on deviation from CONTROL
POINT, plus resets), (2) ACTUAL GUIDE VANE POSITION
compared to the GUIDE VANE TRAVEL LIMIT, (3) VFD
SPEED compared to VFD MAXIMUM SPEED, and (4)
SURGE PREVENTION mode.
Generally the controller will maintain the highest inlet
guide vane setting at the lowest speed to maximize efficiency
while avoiding surge.
First the calculation of GUIDE VANE DELTA is performed.
If GUIDE VANE DELTA is positive, the response will be a
GUIDE VANE POSITION
or VFD SPEED increase (within
limits). If GUIDE VANE DELTA is negative, the response will
be a GUIDE VANE POSITION or VFD SPEED decrease
(within limits). Next, the surge prevention mode is determined
based on location of the present operating point (see Note) in
relation to the configured surge curve. This mode will either be
Normal, Surge Prevention High, or Surge Prevention Low. Ta-
ble 5 indicates which output is modulated first. When the first
output reaches its limit (e.g., ACTUAL GUIDE VANE POSI-
TION reaches maximum), the second output is modulated. The
sequence is the same whether in Surge Prevention High or
Surge Prevention Low.
NOTE: For Constant Flow Surge Prevention, the operating
point is defined by CHILLED WATER DELTA T and ACTIVE
DELTA P. For Variable Primary Flow Surge Prevention the
operating point is defined by GUIDE VANE POSITION and
DELTA TSAT.