Refrigeration Cycle; Motor/Oil Refrigeration Cooling Cycle - Carrier 19XRV Start-Up, Operation And Maintenance Instructions Manual

2.5 - Refrigeration cycle

The compressor continuously draws refrigerant vapour
from the cooler at a rate set by the amount of guide vane
opening. As the compressor suction reduces the pressure
in the cooler, the remaining refrigerant boils at a fairly low
temperature (typically 3 to 6°C). The energy required for
boiling is obtained from the water flowing through the cooler
tubes. With heat energy removed, the water becomes cold
enough for use in an air conditioning circuit or process
liquid cooling.
After taking heat from the water, the refrigerant vapour is
compressed. Compression adds still more heat energy, and
the refrigerant is quite warm (typically 37 to 40°C) when it
is discharged from the compressor into the condenser.
Relatively cool (typically 18 to 3°C) water flowing into
the condenser tubes removes heat from the refrigerant and
the vapour condenses to liquid.
The liquid refrigerant passes through orifices into the FLASC
(Flash Subcooler) chamber (Fig. 1). Since the FLASC
chamber is at a lower pressure, part of the liquid refrigerant
flashes to vapour, thereby cooling the remaining liquid.
The FLASC vapour is recondensed on the tubes which are
cooled by entering condenser water. The liquid drains into a
float chamber between the FLASC chamber and cooler.
Here a float valve forms a liquid seal to keep FLASC cham-
ber vapour from entering the cooler. When liquid refrigerant
passes through the valve, some of it flashes to vapour in the
reduced pressure on the cooler side. In flashing, it removes
heat from the remaining liquid. The refrigerant is now at a
temperature and pressure at which the cycle began.
Condenser
Float valve chamber
Filter drier
Moisture/flow indicator
Orifice fitting
VFD cooling
isolation valve
Thermostatic expansion
valve (TXV)
Unit-mounted VFD
(variable frquency drive)
heat exchanger
VFD cooling
solenoid
8
Fig. 1 - Refrigerant motor cooling and oil cooling cycles
FLASC chamber
Refrigerant cooling
isolation valve
Motor
Stator
Rotor
VFD cooling
Oil
isolation valve
cooler
Oil
filter
Evaporator
Distribution pipe

2.6 - Motor/oil refrigeration cooling cycle

The motor and the lubricating oil are cooled by liquid
refrigerant taken from the bottom of the condenser vessel
(Fig. 1). Flow of refrigerant is maintained by the pressure
differential that exists due to compressor operation. After
the refrigerant flows past an isolation valve, an in-line
filter, and a sight glass/moisture indicator, the flow is split
between motor cooling and oil cooling systems.
Flow to the motor flows through an orifice and into the
motor. Once past the orifice, the refrigerant is directed
over the motor by a spray nozzle. The refrigerant collects
in the bottom of the motor casing and then is drained back
into the cooler through the motor refrigerant drain line. A
back pressure valve or an orifice in this line maintains a
higher pressure in the motor shell than in the cooler/oil
sump. The motor is protected by a temperature sensor
imbedded in the stator windings. A further increase in
motor winding temperature past the motor override setpoint
will override the temperature capacity control to hold, and
if the motor temperature rises 5.5 K above this setpoint,
will close the inlet guide vanes. If the temperature rises
above the safety limit, the compressor will shut down.
Refrigerant that flows to the oil cooling system is regulated
by thermostatic expansion valves (TXVs). The TXVs regulate
flow into the oil/refrigerant plate and frame-type heat
exchanger. The expansion valve bulbs control oil temperature
to the bearings. The refrigerant leaving the oil cooler then
returns to the cooler.
Condenser isolation valve (option)
Orifice fitting
Transmission
Diffuser
Guide
Oil
pump vanes
Impeller
Compressor
Cooler isolation
valve
Condenser water
Guide vane motor
Refrigerant liquid
Refrigerant vapour
Refrigerant liquid/vapour
Oil
Chilled water