14
C6.2.24/1014-0215/E
Figure 16: Suction tube design
3.10 M ufflers
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 acceptability of 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 such as the Alco APD-1 will work quite well. Locate the muffler at minimum
15 cm to maximum 45 cm from the compressor for the most effective operation. The farther the
muffler is placed from the compressor within these ranges, the more effective. Choose a muffler
with a length of 10 to 15 cm.
3.11 Suction line noise and v ibration
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 t o 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 below. The sound phenomena described above are not usually
associated with reversible air conditioning / heat pump systems because of the isolation and
attenuation provided by the reversing valve and tubing bends.
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)
