8
C6.2.27/0716-0219/E
3.5
Screens
CAUTION
Screen blocking! Compressor breakdown!
Use screens with at least
0.6 mm openings.
The use of screens finer than 30 x 30
mesh
(0.6 mm openings) anywhere in the system should be
avoided with these compressors. Field experience has shown that finer mesh screens used to
protect thermal expansion valves, capillary tubes or accumulators can become temporarily or
permanently plugged with normal system debris and block the flow of either oil or refrigerant to
the compressor. Such blockage can result in compressor failure.
3.6
Mufflers
External mufflers, normally applied to piston compressors in the past, may not be required for
Copeland Scroll compressors. Individual system tests should be performed to verify the
acceptability of the sound performance. If adequate attenuation is not achieved, use a muffler with
a larger cross-sectional area to inlet area ratio. A ratio of 20:1 to 30:1 is recommended. A hollow
shell muffler will work quite well. Locate the muffler at minimum 15 to maximum 45 cm from the
compressor for the most effective operation. The further the muffler is placed from the compressor
within these ranges, the more effective. Choose a muffler with a 10
– 15 cm length x 4 cm depth.
3.7
Suction line noise and vibration
Copeland Scroll compressors inherently have low
sound and vibration characteristics. However in
some
respects
the
sound
and
vibration
characteristics
differ
from
reciprocating
compressors and in rare instances could result in
unexpected sound generation. One difference is
that the vibration characteristic of the scroll
compressor, although low, includes 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 can be detected as
noise coming along the suction line into the
building under some conditions. Elimination of the
beat can be achieved by attenuating either of the
contributing frequencies. This is easily done by
using one of the common combinations of recommended design configurations. The scroll
compressor makes both a rocking and twisting 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 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 below.
Recommended configuration
▪
Tubing configuration: ...........small shock loop
▪
Service valve: .....................
"angled” valve fastened to unit / wall
▪
Suction muffler: ....................not required
Alternative configuration
▪
Tubing configuration: ...........small shock loop
▪
Service valve: ......................."straight through" valve fastened to unit / wall
▪
Suction muffler: ....................may be required (acts as dampening mass)
Figure 5: Suction tube design
