Application guidelines
42
FRCC.PC.014.A4.22
Sound and vibration management
Compressor sound radiation
Mechanical vibrations
For sound radiating from the compressor, the
emission path is airborne and the sound waves
are travelling directly from the machine in all
directions.
The VSH scroll compressor is designed to be
quiet and the frequency of the sound generated
is pushed into the higher ranges, which not only
are easier to reduce but also do not generate the
penetrating power of lower-frequency sound.
Use of sound-insulation materials on the inside
of unit panels is an effective means of substan-
tially reducing the sound being transmitted to
the outside. Ensure that no components capable
of transmitting sound/vibration within the unit
come into direct contact with any non insulated
parts on the walls of the unit.
Because of the VSH unique design of a full-suc-
tion gas-cooled motor, compressor body insula-
tion across its entire operating range is possible.
Acoustic hoods are available from Danfoss as
accessories. These hoods are quick and easy to
install and do not increase the overall size of the
compressors to a great extend.
Vibration isolation constitutes the primary meth-
od for controlling structural vibration. VSH scroll
compressors are designed to produce minimal
vibration during operations. The use of rubber
isolators on the compressor base plate or on the
frame of a manifolded unit is very effective in
reducing vibration being transmitted from the
compressor(s) to the unit. Once the supplied
rubber grommets have been properly mounted,
vibrations transmitted from the compressor base
plate to the unit are held to a strict minimum.
In addition, it is extremely important that the
frame supporting the mounted compressor be
of sufficient mass and stiffness to help dampen
any residual vibration potentially transmitted to
the frame. For further information on mounting
requirements, please refer to the section on
mounting assembly.
Typical sound and vibration in refrigeration and
air conditioning systems encountered by design
and service engineers may be broken down into
the following three source categories.
Sound radiation
: this generally takes an airborne
path.
Mechanical vibrations
: these generally extend
along the parts of the unit and structure.
Gas pulsation
: this tends to travel through the
cooling medium, i.e. the refrigerant.
The following sections focus on the causes and
methods of mitigation for each of the above
sources.
For VSH170, an inferior hood is delivered with the
SSH (Surface Sump Heater) to improve its heating
efficiency. Noise level for VSH170 given below
includes this inferior hood attenuation.
For VSH088 and VSH117, inferior hood are not
available.
Sound generation in
a refrigeration or air
conditioning system
Running sound level
Model
Frequency (Hz)
Noise Level (dBA)
VSH088
30
67
60
74
90
84
VSH117
30
68
60
77
90
85
VSH170
30
68 (*)
60
79 (*)
90
88 (*)
Sound power at ARI A/C conditions measured in free space.
(*) Level given with Surface Sump Heater and inferior hood
installed at the bottom of the compressor.
Speed by-pass
Gas pulsation
If vibrations occurs at some typical frequencies
of the VSH variable speed compressor system,
design must be checked: frame, piping, pipes
using cushioned clamps. But if some frequencies
remain showing unacceptable vibration level,
speed by-pass is adjustable in the frequency con-
verter, in order to avoid some frequency ranges.
Four by-pass ranges are adjustable, and settings
can be done in parameters 4.6 *.
The VSH scroll compressor has been designed
and tested to ensure that gas pulsation has been
optimized for the most commonly encountered
air conditioning pressure ratios. On heat pump
installations and other installations where the
pressure ratio lies beyond the typical range,
testing should be conducted under all expected
conditions and operating configurations to en-
sure that minimum gas pulsation is present. If an
unacceptable level is identified, a discharge muf-
fler with the appropriate resonant volume and
mass should be installed. This information can be
obtained from the component manufacturer.
