Sound And Vibration; Compressor Oil Return, Oil Balancing And Flood-Back Tests - Emerson Copeland Scroll ZR24KRE Application Manuallines

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 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

Sound and vibration

3.13
Vibrations during compressor operation can cause cracks which could lead to refrigerant leakage.
This situation must be avoided by the system manufacturer/installer. Therefore, proper pipe design
must be achieved when connecting a scroll compressor to a system.
Figure 15: Example of suction tube design
The sound level of a system is the result of design, quality and application. Scroll compressors sound
power levels generally increase with the compressor model capacity and the condition pressure ratio.

Compressor oil return, oil balancing and flood-back tests

3.14
CAUTION
Inadequate lubrication! Bearing and moving parts destruction! Ensure
adequate oil return from the system into the compressor at any time. No liquid
refrigerant return to the compressor. Liquid refrigerant dilutes the oil, could
wash the oil off the bearings and moving parts and could lead to overheating
and compressor failure.
System piping must be carefully designed to ensure sufficient refrigerant gas velocity, so that oil
returns to the compressor at all times and conditions. Individual piping diameter calculation depends
on the refrigerant properties, pressure level, mass flow, or density.
Once a new system design is set and assembled, a functional test and verification is required. The
functional test includes a qualification for the general system oil return and a refrigerant flood-back
test. Systems with multiple compressor applications (two, three, or more) require additional oil
balancing qualification between the parallel compressors.
A sample compressor equipped with an external oil sight tube can be ordered from Emerson for lab
testing.
During the tests, records of the evaporating temperature and the bottom shell temperature shall be
taken with a high sampling rate. The liquid level in the sight tube has to be observed and noted. If
the system is reversible below tests should be conducted in both operation modes. System engineers
should review the system design and operation to identify the critical conditions and to check oil
return, oil balancing and liquid flood-back. Typically the following situations should be considered:
▪ In single compressor systems to check oil return, testing conditions shall be at minimum mass
flow and minimum density of suction gas in continuous and frequent start-stop-cycling.
▪ In multiple compressor systems to check oil return and oil balancing in the tandem or trio, testing
conditions shall be at the corner points of the system application envelope in continuous and
frequent start-stop-cycling.
▪ In all systems to test liquid flood-back, all possible transient operation conditions in the system
should be checked, eg, compressor frequent start/stop, compressor start after long off with
AGL_AC_ST_ZRKRE_E_Rev01
cm.
A scroll compressor makes both a rocking and twisting motion
and enough flexibility must be provided in the pipe-lines to
allow starting, stopping and steady state running of the
compressor without transmitting excessive stress into any
line attached to the unit. In a split system, the most important
goal is to ensure minimal vibration in all directions to avoid
transmitting vibrations to the structure to which the lines are
fastened.
Under some conditions, the Copeland Scroll has a normal
starting rotational motion that can transmit a transient noise
along the lines. This may be particularly pronounced in
compressors using a three-phase motor due to their
inherently higher starting torque. This phenomenon, like the
one described previously, can easily be avoided by using
standard line isolation techniques.
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