We can consider two means to reduce compressors sound radiations: Acoustic hoods are quick and easy to install
and do not increase the overall size of the compressors.
Acoustic hoods are available from Danfoss as accessories, in "sound and vibration data" section "sound level and
acoustic hood".
The use of sound insulation on the inside of the unit panels is an
effective
way to mitigate sound. You can
find
sound level and acoustic hood accessories in "sound and vibration data" section "sound level and acoustic hood".
Vibrations
Compressor generates some vibrations that propagate into the surrounding parts and structure. The vibration
level of a VCH compressor alone does not exceed 127 μm peak to peak. However, when system structure natural
frequencies are close to running frequency, vibrations are
amplified
due to resonance phenomenon. A high
vibration level is damageable for piping reliability and generates high sound levels.
To avoid resonance phenomenon, pipings and frame must have natural frequencies as far as possible from running
frequencies. This could be challenging on a variable system as all resonant frequencies between minimum speed to
maximum speed will be excited.
It is mandatory to check that piping vibrations are acceptable across speed range. This test can be done by
increasing slowly speed and monitoring piping behaviour through, strain gage, acceleration, or displacement
measurement. As alternative visual check with strobe light can also emphasis high piping displacement.
If some resonant frequencies generate high piping vibration, problem can be solved by increasing piping
stiffness
with brackets or changing layout. Dampers can also be installed to mitigate vibration.
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 4.6x
Ensure that there is no direct contact between vibrating components and structure.
Gas pulsation
The Danfoss VCH scroll compressor has been designed and tested to ensure that gas pulsation is optimized for the
most commonly encountered heat pump pressure ratio.
If an unacceptable level is
identified,
a discharge
muffler
with the appropriate resonant volume and mass can be
installed.
Oil return management
During operation, compressors always discharge amount of oil with refrigerant when start-up. After a while,
some oil will return into the compressor but some will take part in refrigerant cycle or gets trapped somewhere in
the system. When too much oil gets trapped or takes part in refrigerant cycle and doesn't return into the
compressor, compressor may not have enough oil to operate properly.
System with reheat coils, multiple or split evaporator and condenser have a high potential to reduce mass
flow
and
can be susceptible to oil logging. Furthermore, more oil will take part in refrigerant cycle because of large
refrigerant charge quantity.
VCH115 has large speed range and large capacity range. Customer unit design has large deviation such as the
dimension of condenser, evaporator, suction accumulator, pipes. Oil separator installation is mandatory for VCH115
application in order to reduce oil loss risk.
Customer can
define
the oil loss evaluation test according the unit design and application. At the same time,
customer should refer to below general proposal of Danfoss variable speed compressor.
Qualification
of the units
should be done in unfavorable conditions with each feature engaged and disengaged to check oil return
management and oil loss risk of compressor.
© Danfoss | Climate Solutions | 2023.08
AB392939083370en-000202 | 37
Scroll compressors, VCH115 | Application
