Motor And Oil Cooling Cycle; Vfd Cooling Cycle - Carrier AquaEdge 19XR Series Start-Up, Operation And Maintenance Instructions Manual

MOTOR AND OIL COOLING CYCLE

The motor and the lubricating oil are cooled by liquid refrigerant
taken from the bottom of the condenser vessel (Fig. 8 and 9). Re-
frigerant flow is maintained by the pressure differential that ex-
ists due to compressor operation. After the refrigerant flows past
an isolation valve, an in-line filter, and a sight glass/moisture in-
dicator, the flow is split between the motor cooling and oil cool-
ing systems.
CAUTION
To avoid adverse effects on chiller operation, consideration
must be made to condenser water temperature control. For
steady state operation, the minimum operating refrigerant
pressure differential between cooler and condenser is approxi-
mately 20 psi (138 kPa) with a maximum evaporator refriger-
ant temperature of 65°F (18°C). Consult Chiller Builder for re-
quired steady state operational limits. Inverted start conditions
are acceptable for short durations of time, but for periods ex-
ceeding 5 minutes, a special control solution strategy should
be used to allow the chiller to establish a minimum refrigerant
pressure differential, and thereby adequate equipment cooling.
Fig. 7 — Refrigeration Cycle — 19XR(V) Two-Stage Compressor
Flow to the motor cooling system passes through an orifice and
into the motor. Once past the orifice, the refrigerant is directed
over the motor by spray nozzles. The refrigerant collects in the
bottom of the motor casing and is then drained back into the cool-
er through the motor refrigerant drain line. An orifice (in the motor
shell) maintains a higher pressure in the motor shell than in the
cooler. The motor is protected by a temperature sensor embedded
in the stator windings. An increase in motor winding temperature
past the motor override set point overrides the temperature capaci-
ty control to hold, and if the motor temperature rises 10F (5.5C)
above this set point, the controls close the inlet guide vanes. If the
temperature rises above safety limit, the compressor shuts down.
Refrigerant that flows to the oil cooling system is regulated by ex-
pansion valves. The expansion valves regulate flow into the oil/re-
frigerant plate and frame-type heat exchanger (the oil cooler in
Fig. 8), and control oil temperature to the bearings. The refrigerant
leaving the oil cooler heat exchanger returns to the chiller cooler.

VFD Cooling Cycle

The unit-mounted variable frequency drive (VFD) is cooled in a
manner similar to the motor and lubricating oil cooling cycle. If
equipped with a unit-mounted VFD, the refrigerant line that feeds
the motor cooling and oil cooler also feeds the heat exchanger on
the unit-mounted VFD. Refrigerant is metered through an orifice
as refrigerant is leaving the VFD heat exchanger. The refrigerant
leaving the heat exchanger returns to the cooler.
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