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The compressor used by the Series R chiller consists
of three distinct sections: the motor, the rotors and
the bearing housing. Refer to Figure 27 .
Compressor Motor
A two-pole, hermetic, squirrel-cage induction motor
directly drives the compressor rotors. The motor is
cooled by suction vapor drawn from the evaporator
and entering the end of the motor housing (Figure
27) .
Compressor Rotors
Each Series R chiller uses a semi-hermetic, direct-
drive helical rotary type compressor. Excluding the
bearings, each compressor has only 3 moving parts:
2 rotors - "male" and "female" - provide compression,
and a slide valve that controls capacity. See Figure
27 . The male rotor is attached to, and driven by, the
motor, and the female rotor is, in turn, driven by the
male rotor. Separately housed bearing sets are
provided at each end of both rotors on the RTHC
units. The slide valve is located below (and moves
along) the rotors.
The helical rotary compressor is a positive
displacement device. As shown in Figure 27 ,
refrigerant from the evaporator is drawn into the
suction opening at the end of the motor section. The
gas is drawn across the motor, cooling it, and then
into the rotor section. It is then compressed and
released directly into the discharge plenum.
There is no physical contact between the rotors and
compressor housing. Oil is injected into the bottom of
the compressor rotor section, coating both rotors and
the compressor housing interior. Although this oil
does provide rotor lubrication, its primary purpose is
to seal the clearance spaces between the rotors and
compressor housing. A positive seal between these
internal parts enhances compressor efficiency by
limiting leakage between the high pressure and low
pressure cavities.
Capacity control is accomplished by means of a slide
valve assembly located in the rotor/bearing housing
sections of the compressor. Positioned along the
bottom of the rotors, the slide valve is driven by a
piston/cylinder along an axis that parallels those of
the rotors ( Figure 27 ).
Compressor load condition is dictated by the
coverage of the rotors by the slide valve. When the
slide valve fully covers the rotors, the compressor is
fully loaded. Unloading occurs as the slide valve
moves away from the suction end of the rotors. Slide
Installation, Operation and Maintenance
valve unloading lowers refrigeration capacity by
reducing the compression surface of the rotors.
Slide Valve Movement
Movement of the slide valve piston ( Figure 27 )
determines slide valve position which, in turn,
regulates compressor capacity. Compressed vapor
flowing into and out of the cylinder governs piston
movement, and is controlled by the load and unload
solenoid valves, 4L2 and 4L3.
The solenoid valves (both normally closed) receive
"load" and "unload" signals from the UCP2, based on
system cooling requirements. To load the
compressor, the UCP2 opens the load solenoid valve
(4L2). The pressurized vapor flow then enters the
cylinder and, with the help of the lower suction
pressure acting on the face of the unloader valve,
moves the piston over the rotors toward the suction
end of the compressor.
The compressor is unloaded when the unload
solenoid valve (4L3) is open. Vapor "trapped" within
the cylinder is drawn out into the lower-pressure
suction area of the compressor. As the pressurized
vapor leaves the cylinder, the slide valve slowly
moves away from the rotors toward the discharge
end of the rotors.
When both solenoid valves are closed, the present
level of compressor loading is maintained.
On compressor shutdown, the unload solenoid valve
is energized. Springs assist in moving the slide valve
to the fully-unloaded position, so the unit always
starts fully unloaded.
Oil Management System
Oil Separator
The oil separator consists of a vertical cylinder
surrounding an exit passageway. Once oil is injected
into the compressor rotors, it mixes with compressed
refrigerant vapor and is discharged directly into the
oil separator. As the refrigerant-and-oil mixture is
discharged into the oil separator, the oil is forced
outward by centrifugal force, collects on the walls of
the cylinder and drains to the bottom of the oil
separator cylinder. The accumulated oil then drains
out of the cylinder and collects in the oil sump located
near the bottom of the chiller.
4 - 5
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