Application Engineering
B U L L E T I N
AE4-1374 R1
attenuation is not achieved, use a muffler with a larger
cross-sectional area to inlet-area ratio. The ratio should
be a minimum of 20:1 with a 30:1 ratio recommended.
The muffler should be from four to six inches (10 -15
cm) long.
Air Conditioning System Suction Line Noise and
Vibration
Copeland Scroll compressors inherently have low sound
and vibration characteristics. However, the sound and
vibration characteristics differ in some respects from
those of reciprocating compressors. In rare instances,
these could result in unexpected sound complaints.
One difference is that the vibration characteristics of the
scroll compressor, although low, include two very close
frequencies, one of which is normally isolated from the
shell by the suspension of an internally suspended
compressor. These frequencies, which are present in all
compressors, may result in a low level
“beat” frequency
that may be detected as noise coming along the suction
line into a house under some conditions. Elimination
of the
“beat” can be achieved by attenuating either
of the contributing frequencies. The most important
frequencies to avoid are 50 and 60 Hz power supply line
and twice-line frequencies for single-phase compressors
and line frequency for three phase compressors. This is
easily done by using one of the common combinations
of design configuration described in Table 2. The scroll
compressor makes both a rocking and torsional motion,
and enough flexibility must be provided in the line to
prevent vibration transmission into any lines attached to
the unit. In a split system the most important goal is to
ensure minimal vibration in 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 may be
particularly pronounced in three-phase models due to
their inherently higher starting torque.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 2.
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.
© 2013 Emerson Climate Technologies, Inc.
Printed in the U.S.A.
Mounting Parts
Table 3 lists the mounting parts to be used with
these compressors. Many OEM customers buy the
mounting parts directly from the supplier, but Emerson
’s
grommet design and durometer recommendation
should be followed for best vibration reduction through
the mounting feet. Please see AE4-1111 for grommet
mounting suggestions and supplier addresses.
Single Phase Starting Characteristics
Start assist devices are usually not required, even if
a system utilizes non-bleed expansion valves. Due to
the inherent design of the Copeland Scroll compressor,
the internal compression components always start
unloaded even if system pressures are not balanced. In
addition, since internal compressor pressures are always
balanced at startup, low voltage starting characteristics
are excellent for Copeland Scroll compressors. The
starting Locked Rotor Amperage (LRA), also referred
to as inrush current, is normally six or more times higher
than the rated running amperage of the compressor
and lasts from 100 to 300 milliseconds until the rotor
starts turning. This high starting current may result in
significant
“sag” in voltage where a poor power supply
is encountered. Low starting voltage reduces the starting
torque of the compressor and subsequently increases
the time the compressor is in a locked rotor condition.
This could cause light dimming or a buzzing noise
where wire is pulled through conduit. Start components
will substantially reduce start time and consequently
the magnitude and duration of both light dimming and
conduit buzzing. Specified starting components can be
found in the Online Product Information section of www.
emersonclimate.com.
PTC Start Components
For less severe voltage drops or as a start boost, solid
state Positive Temperature Coefficient (PTC) devices
rated from 10 to 25 ohms may be used to facilitate
starting for any of these compressors.
Electrical Connections
WARNING
Molded electrical plug (Emerson p/n 529-0060-
04 or OEM equivalent) must be used in all
applications.
The orientation of the electrical connections on the
Copeland Scroll compressors is shown in Figure 4.
ZR*K5 compressors have one electrical connection
option, the one piece push-on molded electrical plug.
ZR*K5 compressors are not available with traditional
9
