Trane R Series Installation Operation & Maintenance page 58

Refrigerant R134a
The RTAC chiller uses environmentally
friendly R134a. Trane believes that
responsible refrigerant practices are
important to the environment,
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.
R134a is a medium pressure refrigerant.
It may not be used in any condition that
ould cause the chiller to operate in a
vacuum without a purge system. RTAC
is not quipped 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.
R134a requires the use of specific POE
oils as designated on the unit nameplate.
Important! The RTAC units must only
operate with R-134a and Trane Oil
00048.
Compressor
The compressor is a semi-hermetic,
direct-drive rotary type
Each compressor has
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 the evaporator
is drawn into the suction opening of the
compressor (state 1b), through 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
58
Operating Principles
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
our 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
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.
Condenser and Subcooler
The condenser and subcooler are similar
to the condenser used in RTAA chillers.
The heat exchanger consists of 3/8"
tubes that contain the refrigerant, large
fins that are in the air flow and fans
compressor.
that draw air through the fins. Heat is
only four
transferred from the refrigerant through
the tubes and fins to the air.
High pressure gas from the compressor
enters the tubes of the condenser
through a istribution header (state
2b). As refrigerant flows through the
tubes, the heat of compression and
cooling load are rejected to the air.
In this process the refrigerant is de-
superheated, condensed (states 2b to 3)
and finally subcooled (states 3 to 3b) to
a temperature slightly above the ambient
air temperature. The subcooled liquid
refrigerant is collected in the leaving
header where it is transferred to the
liquid line (state 3b).
efficiency by limiting
A controls algorithm always runs as
many fans as possible without reducing
the differential pressure
minus suction) below the setpoint (60
psid or 4.2 bar). If a warm enough
ambient is sensed, all the fans will
run. If the ambient is cooler, some fans
are shut off to maintain the pressure
differential. Fan staging depends on
the chiller load, evaporator pressure,
condenser effectiveness,
temperature, and numbers and sizes of
fans installed on the circuit.
The algorithm pre-starts fans (based on
ambient and water temperatures) when
a circuit starts the compressor. (For rare
conditions such as during some pull-
downs, a steady fan state would either
violate the 60 psid (4.2 bar) setpoint or
cause a high pressure cut-out; in those
conditions a fan will cycle on and off.)
For up to two minutes after chiller start-
up, the setpoint is 35 psi (2.45 bar)
difference, and then before the controls
adjust gradually over half a minute up to
60 psi (4.2 bar).
Expansion Valve
Pressure drop occurs in an electronic
expansion valve. The unit controller
(CH530) uses the valve to regulate the
flow through the liquid line to match
the flow produced by the compressor.
The valve has a variable orifice that is
modulated by a stepper motor.
High pressure, subcooled
refrigerant enters the expansion valve
from the liquid line. As refrigerant
passes through the valve the pressure
is dropped substantially, which results in
vaporization of some of the refrigerant.
The heat of vaporization is supplied by
the two phase mixture resulting in low
temperature low pressure refrigerant
which is supplied to the evaporator (state
4) to provide cooling.
RTAC-SVX002A-EN
(discharge
ambient
liquid