Installation and Maintenance Manual

40 RTAE-SVX001B-EN
Operating Principals
This section contains an overview of the operation and
maintenance of Stealth RTAE units equipped with UC800
control systems. It describes the overall operating
principles of the RTAE design.
Refrigeration Circuits
Each unit has two refrigerant circuits, with one rotary
screw compressor per circuit. Each refrigerant circuit
includes a compressor suction and discharge service
valve, liquid line shutoff valve, removable core filter, liquid
line sight glass with moisture indicator, charging port and
an electronic expansion valve. Fully modulating
compressors and electronic expansion valves provide
variable capacity modulation over the entire operating
range. Lower condensing temperatures and higher
suction temperatures along with more efficient
compressors and fans result in the premium efficiency
level of Stealth Air Cooled chillers
Refrigeration Cycle
The refrigeration cycle of the RTAE chiller is represented in
the pressure enthalpy diagram shown in Figure 26.Key
state points are indicated on the figure.The cycle for the
full load AHRI design point is represented in the plot.
The RTAE 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 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 removes 99.8% of the
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 RTAE chiller uses environmentally friendly R-134a.
Trane believes that responsible refrigerant practices are
important to the environment, our customers, and the air
conditioning industry. All technicians who handle
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. RTAE is not
equipped with a purge system.Therefore, the RTAE 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 00311 (bulk)/
00315 (1gal)/00317 (5gal) in Stealth chillers.
Compressor and Lube Oil System
The rotary screw compressor is semi-hermetic, direct
drive with capacity control via a variable speed drive,
rolling element bearings, differential refrigerant pressure
oil pump and oil heater.The motor is a suction gas cooled,
hermetically sealed, permanent magnet motor. An oil
separator is provided separately from the compressor. Oil
filtration is provided internal to the compressor. Check
valves in the compressor discharge and lube oil system
are also provided.
Condenser and Fans
Air-cooled condenser coils have aluminum fins
mechanically bonded to internally finned seamless
aluminum tubing.The tubing is a long life alloy designed
to deliver corrosion performance that meets or exceeds
microchannel coils.The condenser coil has an integral
subcooling circuit. Condensers are factory proof tested at
525 psig and leak tested with helium in a mass
spectrometer chamber at 150 psig. All tube connections
are mechanical except the brazed copper to aluminum
inlet and outlet connections. Condenser fans are direct-
drive vertical discharge.The condenser fan motors are
permanent magnet motors with an integrated drive to
Figure 26. Pressure enthalpy (P-h) diagram - RTAE
R-134a
h (btu/lb)
P (psia)
1
1b
2
2b
3
3b
4
120 140100806040200
30
50
100
200
500
600