Table of Contents
Advertisement
3.11 Sound and vibration
Vibrations during compressor operation can cause cracks which could lead to refrigerant leak age.
This situation must be avoided by the system manufacturer/installer. To t his end, t he p ipework
must be carefully designed when connecting a scroll compressor to a system.
Figure 15: Suction tube design
The sound level of a system is the result of design, quality and application. S cro ll c ompress ors
sound power levels generally increase with the compressor model capac it y and t he c ondition
pressure ratio.
3.12 Compressor oil return, oil balancing and floodback tests
CAUTION
Inadequate lubrication! Bearing and moving parts destruction! E nsure
adequate oil return from the system into the c ompres sor at any t ime. No
liquid refrigerant return to the compressor. Liquid refrigerant dilutes t he o il,
could wash the oil of f the bearings and moving parts and could lead to
overheating and compressor failure.
The system piping must be carefully designed to ensure sufficient refrigerant gas velocity, so t hat
oil returns to the compressor at all times and conditions. Individual p iping d iameter c alculation
depends on the refrigerant properties, pressure level, mass flow, and density.
Once a new system design is set and assembled, a f unctional test is required. The f unctional t est
includes a qualification for the general system oil return and a ref rigerant floodback test . S ys tems
with multiple compressor applications (two, three, or more) require additional oil balancing
qualif ication between the parallel compressors.
A sample compressor equipped with an external oil sight tube can be ordered from Emerson for lab
testing.
Records of the evaporating temperature and the bottom shell temperature s hall be t ak en wit h a
high sampling rate during the entire oil return or oil balance testing and under all tested conditions.
The liquid level in the sight tube has to be observed and recorded too. Tes t ing c ondit ions shall
include defrost and varying loads. If the system is reversible, the tests should be conducted in both
operation modes.
System engineers should review the system design and operation to identify the critical condit ions
and to check oil return, oil balancing and liquid floodback. Typically, the following situations should
be considered:
▪ In single compressor systems: to check oil return, testing conditions s hall be at minimum
mass f low 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 t andem o r t rio,
testing conditions shall be at the corner points of the system application envelope in continuous
and f requent start-stop-cycling.
▪ In all systems: to test liquid floodback, all possible transient operation conditions in the syst em
should be checked, eg, compressor frequent start/stop, compressor start after long off time with
migration, defrost, switching between the operation modes in reversible systems, load changes,
AGL_HP_ST_ZHK1P_EN_Rev00
A scroll compressor makes both a rocking and twisting
motion and enough flexibility must be provided in t he
pipe-lines to allow starting, stopping and steady st ate
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 transmitt ing
vibrations to the structure to which the lines are
f astened.
Under some conditions, the Copeland scroll has a
normal starting rotational motion that c an trans mit 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 us ing s t andard
line isolation techniques.
15
Advertisement
Table of Contents
