Operating Principles; Refrigeration Cycle; Refrigerant R-134A; Compressor - Trane R Series Installation, Operation And Maintenance Manual

Operating Principles

This section contains an overview of the operation and
maintenance of RTAC units equipped with CH530 control
systems. It describes the overall operating principles of the
RTAC design.

Refrigeration Cycle

The refrigeration cycle of the RTAC chiller is similar to that
of the RTAA air cooled water chiller.The exception is that
the evaporating and condensing temperatures have been
increased to allow for optimization of the chiller and
reduced foot print.The refrigeration cycle is represented
in the pressure enthalpy diagram in
points are indicated on the figure.The cycle for the full
load ARI design point is represented in the plot.
Figure 31. Pressure enthalpy (P-h) diagram - RTAC
600
500
200 3b
100
4
4b
50
30
0 20 40
The RTAC chiller uses a shell and tube evaporator design
with refrigerant evaporating on the shell side and water
flowing inside tubes having enhanced surfaces (states 4 to
1).The suction lines and bolt pads are designed to
minimize pressure drop.(states 1 to 1b).The compressor is
a twin-rotor helical rotary compressor designed similarly
to the compressors offered in otherTrane Screw
Compressor Based Chillers (states 1b to 2).The discharge
lines include a highly efficient oil separation system that
virtually removes all oil from the refrigerant stream going
to the heat exchangers (states 2 to 2b). De-superheating,
condensing and sub-cooling is accomplished in a fin and
tube air cooled heat exchanger where refrigerant is
condensed in the tube (states 2b to 3b). Refrigerant flow
through the system is balanced by an electronic expansion
valve (states 3b to 4).

Refrigerant R-134a

The RTAC chiller uses environmentally friendly R134a.
Trane believes that responsible refrigerant practices are
important to the environment, our customers, and the air
conditioning industry. All technicians who handle
106
Figure 31. Key state
R-134a
137°F (58°C)
3
126°F (52°C)
106°F (41°C)
1
39°F (4°C)
1b
60 80 100 120
h (btu/lb)
refrigerants must be certified.The Federal Clean Air Act
(Section 608) sets forth the requirements for handling,
reclaiming, recovering and recycling of certain
refrigerants and the equipment that is used in these
service procedures. In addition, some states or
municipalities may have additional requirements that
must also be adhered to for responsible management of
refrigerants. Know the applicable laws and follow them.
R-134a is a medium pressure refrigerant. It may not be
used in any condition that would cause the chiller to
operate in a vacuum without a purge system. RTAC is not
equipped with a purge system.Therefore, the RTAC chiller
may not be operated in a condition that would result in a
saturated condition in the chiller of –15°F (-26°C) or lower.
R-134a requires the use of specific POE oils as designated
on the unit nameplate.
Important: Use only R-134a andTrane Oil 00048 in
RTAC chillers.

Compressor

2
2b
The compressor is a semi-hermetic, direct-drive rotary
type compressor. Each compressor has only four moving
parts: two rotors that provide compression and male and
female load-control valves.The male rotor is attached to
the motor and the female rotor is driven by the male rotor.
The rotors and motor are supported by bearings.
The helical rotary compressor is a positive displacement
device. Refrigerant vapor from evaporator is drawn into
the suction opening of the compressor (state 1b), through
140 a suction strainer screen across the motor (which provides
motor cooling) and into the intake of the compressor
rotors.The gas is then compressed and discharged
through a check valve and into the discharge line (state 2).
There is no physical contact between the rotors and the
compressor housing.The rotors contact each other at the
point where the driving action between the male and
female rotors occurs. Oil is injected into the rotors of the
compressor, coating the 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 female
step load-control valve and a male control valve.The
female step valve is the first stage of loading after the
compressor starts and the last stage of unloading before
the compressor shuts down.The male control valve is
positioned by a piston cylinder along the length of the
male rotor. Compressor capacity is dictated by the
position of the loading valve relative to the rotors. When
the valve slides toward the discharge end of the rotors
compressor capacity is reduced.
RTAC-SVX01J-EN