Single compressors
Sound and vibration management
Compressor sound
radiation
Mechanical vibrations
Speed by-pass
Gas pulsation
For sound radiating from the compressor, the
emission path is airborne and the sound waves
travel directly from the machine in all directions.
The VZH 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 substantially
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 VZH unique design of a full-
suction gas-cooled motor, compressor body
insulation 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 extent.
Vibration isolation constitutes the primary
method for controlling structural vibration. VZH
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.
If vibrations occurs at some typical frequencies
of the VZH variable speed compressor system,
design must be checked: frame, piping,
pipes using cushioned clamps. But if some
frequencies continue to produce unacceptable
vibration levels, speed by-pass is adjustable
in the frequency converter, in order to avoid
some frequency ranges. Four by-pass ranges
are adjustable, and settings can be made in
parameter group 4-6.
The VZH 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
ensure that minimum gas pulsation is present. If
an unacceptable level is identified, a discharge
muffler with the appropriate resonant volume
and mass should be installed. This information
can be obtained from the component
manufacturer.
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.
Sound generation in a
refrigeration or air
conditioning system
Running sound level
For all VZH models, noise level given in table does not include bottom hood attenuation.
Model
Frequency RPS
200 V
400 V
Without accoustic hood
(dBA)
With accoustic hood
(dBA)
Without accoustic hood
(dBA)
With accoustic hood
(dBA)
VZH028-044
60
77
70
77
70
100
86
79
86
79
Average sound power for reference at ARI A/C conditions measured in free space.
Please notice below two phenomenon is also normal for variable speed compressor:
1. At light load and low speed condition the compressor may produce certain discharge pulsation.
2. In some situations when the compressor stops working, there may still be some noise which lasts around 2 seconds. The electromagnetic noise is caused by drive anti-reverse
protection.
35
FRCC.PC.034.A2.02
Application Guidelines
