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Operating Principles
This section describes the overall operating principles of
the Ascend™ ACR chiller with Symbio™ controls.
Refrigeration Circuits
Each unit has two refrigerant circuits, with a minimum of
one rotary screw compressor per circuit. Each refrigerant
circuit includes compressor suction and discharge service
valves, 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.
Refrigeration Cycle
The refrigeration cycle of the chiller is represented in the
pressure enthalpy diagram shown in figure below. Key
state points are indicated on the figure. The cycle for the
full load AHRI design point is represented in the plot.
Figure 26. Pressure-enthalpy (P-h) diagram
600
500
3
200
3b
100
4
50
30
0
20
40
The 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 other Trane 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 or microchannel
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).
74
1
1b
60
80
100
120
h (btu/lb)
Refrigerant
The Ascend™ ACR chiller uses environmentally friendly R-
513A. Trane believes 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.
Refrigerant R-513A 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.
Ascend™ ACR is not equipped with a purge system.
Therefore, the chiller may not be operated in a condition
that would result in a saturated condition in the chiller of
-20°F (-29°C) or lower.
Refrigerant R-513A requires the use of specific POE oils as
designated on the unit nameplate.
Important: Use only R-513A refrigerant and Trane
OIL0075E / OIL0076E (5 gallon).
Compressor and Oil System
2
Each rotary screw compressor is semi-hermetic, direct
2b
drive with capacity control via a variable speed drive, rolling
element bearings, differential refrigerant pressure oil pump
and oil heater. To maximize efficiency, the variable Vi
(variable pressure ratio) compressor is controlled to one of
two possible states depending on the chiller system
operating point and to provide ease of starting. 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
140
compressor. Check valves in the compressor discharge
and lube oil system are also provided.
Condenser and Fans
Air-cooled microchannel condenser coils use all Long Life
Alloy aluminum brazed fin construction. The condenser will
have an integral subcooling circuit. The maximum
allowable working pressure of the condenser is 350 psig
(2412 kPa).
The condenser coil has an integral subcooling circuit.
Condensers are factory proof tested and leak tested.
Condenser fans are direct-drive vertical discharge. The
condenser fan motors are permanent magnet motors with
integrated drive to provide variable speed fan control for all
fans. Fans are designed with permanently lubricated ball
bearings, internal temperature and current overload
protection, and customer fault feedback as a standard
AC-SVX003A-EN
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