System information

25
ECONOMIZER DAMPER VALVE CONTROL — The
economizer damper valve control maintains the difference be-
tween evaporator pressure and economizer pressure. Econo-
mizer pressure should always be higher than evaporator pres-
sure.
NOTE: If the Chiller Type (Configuration Menu  Factory
Parameters) is configured to Legacy, the economizer damper
valve control is bypassed.
When the chiller is initially powered on, or when the com-
pressor shuts down, the damper valve will be commanded to
close. These and other conditions are shown in Table 13.
Table 13 — Economizer Damper Valve Status
If the damper valve has been commanded to open for a con-
tinuous 5 minutes, and the Damper Valve Full Opened condi-
tion is still not TRUE, the control system generates an alert
154. Similarly, if the damper valve has been commanded to
close for a continuous 5 minutes, and the Damper Valve Full
Closed condition is still not TRUE, the control system gener-
ates an alert 154.
If the compressor is running and if economizer pressure be-
comes less than or equal to evaporator pressure, an alarm 268
will be tripped and compressor will be shut down.
DEMAND LIMIT — The PIC 5 controls provide a feature for
limiting AVERAGE LINE CURRENT or MOTOR KILO-
WATTS by limiting capacity via guide vane control/VFD con-
trol. The limit may be applied in two ways. The first is called
ACTIVE DEMAND LIMIT, which is equal to a BASE DE-
MAND 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
overriding (forcing) the value via a CCN network device. If
the DEMAND LIMIT SOURCE exceeds the ACTIVE DE-
MAND LIMIT 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.
Alternatively, the limit may be applied by by AUTO DE-
MAND LIMIT INPUT, an optional 4 to 20 mA input. This de-
mand limit control option (4-20 mA DEMAND LIMIT TYPE)
is externally controlled by a 4 to 20 mA signal. The option is
set up on the Configuration Menu  GENERAL CONFIGU-
RATION screen. When enabled, 4 mA will set ACTIVE DE-
MAND LIMIT to 100% of the DEMAND LIMIT SOURCE
(regardless of the value of BASE DEMAND LIMIT), and 20
mA will set ACTIVE DEMAND LIMIT to the value config-
ured for DEMAND LIMIT AT 20 mA in the Configuration
Menu  SERVICE PARAMETERS screen.
OVERRIDE CONTROL — Capacity overrides can prevent
some safety shutdowns caused by exceeding the motor amper-
age limit, evaporator refrigerant low temperature safety limit,
motor high temperature safety limit, and condenser high pres-
sure limit. In these cases there are two stages of capacity con-
trol:
1. When the value of interest crosses the first stage set point
into the override region, the capacity is prevented from
increasing further, and the status line on the PIC 5 con-
troller indicates the reason for the override. Normal ca-
pacity control operation is restored when the value cross-
es back over the first stage set point, leaving the override
region.
2. When the value of interest is in the override region and
further crosses the second stage set point, the capacity is
decreased until the value meets the override termination
condition. The PIC 5 controls resume normal capacity
control operation after the override termination condition
has been satisfied. (In the case of high discharge super-
heat, there is an intermediate stage.)
Table 14 summarizes these override parameters.
Table 14 — Override Parameters
*EVAP SAT OVERRIDE TEMP = EVAP TRIPPOINT + EVAP OVER-
RIDE DELTA T
SYSTEM CONDITION
ECONOMIZER DAMPER
VALVE STATUS
Chiller initially powered on Fully closed
Compressor shut down Fully closed
During damper valve action delay Fully closed
Economizer pressure > evapora-
tor pressure + Damper valve open
DB
Open
Economizer pressure < evapora-
tor pressure + Damper valve close
DB
Closed
All other conditions Current position maintained
OVERRIDE CONDITION
OVERRIDE
PARAMETER
FIRST STAGE
CAPACITY
INHIBIT
DEFAULT VALUE/
CONFIGURABLE
RANGE
SECOND STAGE
CAPACITY
DECREASE
OVERRIDE
TERMINATION
High condenser pressure
override
(high pressure vessel/heat
machine)
CONDENSER
PRESSURE
> COND PRESS
OVERRIDE HIGH
250 psig/200-260
psig
> COND PRESS
OVERRIDE HIGH +
2.4 psi
< COND PRESS
OVERRIDE HIGH
High condenser pressure
override
(low pressure vessel/cool
only)
CONDENSER
PRESSURE
> COND PRESS
OVERRIDE LOW
140 psig/90-150 psig > COND PRESS
OVERRIDE LOW +
2.4 psi
< COND PRESS
OVERRIDE LOW
Low evaporator tempera-
ture override
CALC EVAP SAT TEMP
or
EVAP REFRIG LIQUID
TEMP
< EVAP SAT
OVERRIDE
TEMP*
< EVAP SAT OVER-
RIDE TEMP - 1 F
(0.56 C)
> EVAP SAT
OVERRIDE TEMP
High motor temperature
override
COMP MOTOR WIND-
ING TEMP
> COMP MOTOR
TEMP OVERRIDE
200 F/150-200 F
(93.3 C/65.6-93.3 C)
COMP MOTOR
WINDING TEMP >
COMP MOTOR
TEMP OVERRIDE +
10 F (5.6 C)
COMP MOTOR
WINDING TEMP <
COMP MOTOR
TEMP OVERRIDE
– 2 F (1.1 C)
High current override PERCENT LINE CUR-
RENT
PERCENT LINE
CURRENT >
100%
PERCENT LINE
CURRENT > 105%
PERCENT LINE
CURRENT <=
100%
Low discharge superheat
override
Discharge Superheat
(DSH)
< DSH
REQUIRED + 1
< DSH REQUIRED –
3
> DSH REQUIRED
+ 2
Low source temperature
protection override
Leaving chilled water
temperature (heating
mode)
< COOLING LCW
SETPOINT – 2° F
(1.1° C)
> COOLING LCW
SETPOINT – 2° F
(1.1° C)