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C6.2.15/0815/E
3.13 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. The sound phenomena described above are not usually associated with
reversible 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)
