Trane CITY RTSF Series Manual page 30

Operating Principles Mechanical
Compressors
The compressor used by the chiller consists of 3 distinct sections: the motor, the rotors and the bearing housing.
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 through the suction line.
Compressor Rotors
Each 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. 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. Female and male unloader
piston moves along the respective rotor.
The helical-rotary compressor is a positive displacement device. Refrigerant from the evaporator is drawn into
the suction opening at the end of the motor section. The gas is drawn through a suction strainer across the motor,
cooling it, and then into the rotor section. It is then compressed and discharged directly into the discharge line.
There is no physical contact between the rotors and compressor housing. Oil is injected through adequate ports,
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 effi ciency by limiting leakage between the high pressure and low pressure
cavities.
Capacity control is accomplished by means of male and female unloader piston.
Slide Valve movement
Slide valve operates coordinated with AFD. Tracer UC800 algorithm controls the compressor capacity with higher
slide valve capacity and lower AFD frequency to get higher effi ciency
This loading/unloading schema is a general fi gure, it could be different in case of sudden modifi cations of
the operating data. Also it has not to be considered as a starting/stopping mode.
Slide Valve
Loading
Unloading
Above 71.1°C condenser saturated temperature in order to allow suffi cient motor cooling there is no possibility to
decrease frequency below
- 50Hz for sizes 050 to 090
- 60Hz for sizes 100 and 110
Figure 7 – Compressor description
30
AFD
30 Hz 50 Hz
60% 100%
Capacity Capacity
60% 100%
Capacity Capacity
A = Oil control valve (hidden)
B = Female unloader piston
C = Discharge check valve
D = Female rotor
E = Motor terminals
F = Suction strainer
G = Motor rotor
H = Male unloader piston
I = Male rotor
J = Oil fi lter
RLC-SVX023B-GB