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© 2016 Emerson Climate Technologies, Inc.
AE4-1303 R15
attached to the unit. In a split system the most important
goal is to ensure minimal vibration is all directions at
the service valve to avoid transmitting vibrations to the
structure to which the lines are fastened.
A second difference of the Copeland Scroll compressor
is that under some conditions the normal rotational
starting motion of the compressor can transmit an
“impact” noise along the suction line. This phenomenon,
like the one described previously, also results from the
lack of internal suspension, and can be easily avoided
by using standard suction line isolation techniques as
described in
Table 3
.
The sound phenomena described above are not usually
associated with heat pump systems because of the
isolation and attenuation provided by the reversing valve
and tubing bends.
Suction and Discharge Fittings
Copeland Scroll compressors have copper plated steel
suction and discharge fittings. These fittings are far
more rugged and less prone to leaks than copper fittings
used on other compressors. Due to the different thermal
properties of steel and copper, brazing procedures
may have to be changed from those commonly used.
See
Figure 6
for assembly line and field brazing
recommendations.
System Tubing Stress
System tubing should be designed to keep tubing
stresses below 9.5 ksi (62 MPa), the endurance limit
of copper tubing. Start, stop and running (resonance)
cases should be evaluated.
Accumulators
The use of accumulators is very dependent on the
application. The Copeland Scroll
™
compressor’s inherent
ability to handle liquid refrigerant during occasional
operating flood back situations makes the use of an
accumulator unnecessary in standard designs such as
condensing units. Applications such as heat pumps with
orifice refrigerant control that allow large volumes of
liquid refrigerant to flood back to the compressor during
normal steady operation can dilute the oil to such an
extent that bearings are inadequately lubricated, and
wear will occur. In such a case an accumulator must
be used to reduce flood back to a safe level that the
compressor can handle. Heat pumps designed with a
TXV to control refrigerant during heating may not require
an accumulator if testing assures the system designer
that there will be no flood back throughout the operating
range. To test for flood back conditions and to determine
if the accumulator or TXV design is adequate, please
see the section entitled
Application Tests
.
A large-area protective screen no finer than 30x30
mesh (0.6mm openings) is required to protect this small
orifice from plugging. Tests have shown that a small
screen with a fine mesh can easily become plugged
causing oil starvation to the compressor bearings. The
size of the accumulator depends upon the operating
range of the system and the amount of sub cooling and
subsequent head pressure allowed by the refrigerant
control. System modeling indicates that heat pumps
that operate down to and below 0°F (-18°C) will require
an accumulator that can hold around 70% to 75% of
the system charge. Behavior of the accumulator and
its ability to prevent liquid slugging and subsequent oil
pump-out at the beginning and end of the defrost cycle
should be assessed during system development. This
will require special accumulators and compressors
with sight tubes and/or sight glasses for monitoring
refrigerant and oil levels.
Crankcase Heat
A 90 watt crankcase heater is required when the
system charge exceeds the values listed in
Table 5
.
This requirement is independent of system type and
configuration.
Table 5
lists Emerson crankcase heaters
by part number and voltage. See
Figure 6
for the proper
heater location on the compressor shell.
The crankcase
heater must remain energized during compressor
off cycles.
The initial start-up in the field is a very critical period for
any compressor because all load-bearing surfaces are
new and require a short break-in period to carry high
loads under adverse conditions.
The crankcase heater
must be turned on a minimum of 12 hours prior to
starting the compressor.
This will prevent oil dilution
and bearing stress on initial start up.
To properly install the crankcase heater, the heater
should be installed in the location illustrated in
Figure
5.
Tighten the clamp screw carefully, ensuring that the
heater is uniformly tensioned along its entire length
and that the circumference of the heater element is
in complete contact with the compressor shell. It's
important that the clamp screw is torqued to the range
