4.3 - Cooler Interlock contact
A contact to check the status of a safety loop is provided (cooler flow switch and customer interlock are wired
internally in series). Its function is to prevent the unit from starting if the contact is open while the delay at startup has
expired. The contact must also stay closed as long as the unit is not stopped through Local, Remote or CCN control.
If the cooler pump is controlled by the pro-dialog and if the cooler contact is closed after 2 minutes the cooler pump
is turned OFF provided that the contact is failed CLOSED, the alarm 75 shall be active and the unit can't no more
start until manual reset.
4.4 - Cooler heater control
This function is applied only for air cooled units and is related to the cooler pump function when the unit state is OFF
or when unit operates as a lag chiller in master/slave operation and in standby mode. This is provided on outdoor
unit as a safeguard against the cooler freezing. The cooler heater is associated with refrigerant isolation solenoids,
one output per circuit whose goal is to prevent the refrigerant from migrating into the condenser when chiller is
stopped.
The following logic shall be used:
w
If the outdoor air temperature is below the cooler heater trip point and if either the saturated suction temperature
of circuit A or saturated suction temperature of circuit B are lower than the cooler heater trip point plus 3.3 ^C,
the cooler heater shall be activated.
w
Normally the isolation valves shall prevent refrigerant in the cooler from migrating into the condenser. For this
case, cooler heater can ensure cooler protection efficiently without the need of using cooler pump.
w
If it is not the case (SST remain low), the pump shall be turned on every 7 minutes to check freezing conditions
and additional heat to the cooler : cooler fluid temp (< 3° - [SSTa + SSTb]/2). Pump shall be turned of if cooler
fluid temp > (8°C - [SSTa + SSTb]/2).
w
If both saturated suction temperatures of circuit A and circuit B are greater than the cooler heater trip point plus
5.5 ^C, the cooler heater shall be turned off. The pump shall be allowed to stop.
heater trip point = heat_spt (heat_sp from SERVICE2 table)
freeze = 1.1 for water, coldest setpoint - 4.4^C for brine
4.5 - Oil heater control
Each circuit has its own oil separator fitted with an oil heater. Both circuit oil heater are controlled independently .
Since there is no oil temperature sensor, the oil heater will be controlled based on the saturated condensing
temperature as follows :
w
Oil heater ON when outside temperature is below 17°C.
w
Oil heater OFF when outside temperature is above 25°C
w
Oil heater OFF when circuit is in operation or oil level is low (oil_sw is OPEN).
4.6 - Motor Cooling Control without plate exchanger economizer
The screw compressor motors used in the Global Chiller control are refrigerant cooled. The control strategy for motor
cooling relies on vapor at light loads, and supplementary liquid refrigerant at high loads. Each compressor will have
its own cooling solenoid. An additional motor cooling solenoid is required when operating in high condensing
temperature. It is automatically controlled by pro-dialog even if it is not mounted in the units. The motor cooling
solenoids shall be cycled to allow liquid to cool the motor. The main motor cooling solenoid control is based on the
motor temperature and its setpoint (83°C) using a quasi-fuzzy logic. The additional motor cooling solenoid control is
just based on the discharge gas temperature.
CARRIER SA
USER'S GUIDE FOR
30GX&HX PRO_DIALOG 4 V.2
ECG-UG-02-002
Rev: Original
Page: 36/98
©
C
ARRIER
S
.
A
NOT
TO
BE
DISCLOSED
TO
PERSONS
OUTSIDE
CARRIER
ORGANIZATION
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