16
C6.2.15/0815/E
3.8 Oil separator
During any operating cycle of Copeland Scroll Digital compressors, there is a loaded state during
which the compressor operates at full capacity. The velocity of gas during this loaded state is
sufficient to return oil back to the compressor. Laboratory tests have established that there is no
problem in oil return, even when the length of interconnecting pipe used is
100 metres and the vertical elevation is 30 metres. Based on such performance, Emerson
Climate Technologies does not strictly recommend the use of an oil separator.
3.9 Accumulators
CAUTION
Inadequate lubrication! Bearing destruction!
Minimise liquid refrigerant
returning to the compressor. Too much refrigerant dilutes the oil. Liquid
refrigerant can wash the oil off the bearings leading to overheating and
bearing failure.
Due to Copeland Scroll’s inherent ability to handle liquid refrigerant in flooded start and defrost
cycle operation, an accumulator is not required for durability in most systems. However, large
volumes of liquid refrigerant which repeatedly flood back to the compressor during normal off
cycles or excessive liquid refrigerant floodback during defrost or varying loads, no matter what
the system charge is, can dilute the oil. As a result, bearings are inadequately lubricated and
wear may occur.
To determine if the accumulator can be removed, dedicated tests must be carried out to ensure
that excessive liquid does not flood back to the compressor during defrost or varying loads. The
defrost test must be done at an outdoor ambient temperature of around 0°C in a high humidity
environment. Liquid floodback must be monitored during reversing valve operation, especially
when coming out of defrost.
Excessive floodback occurs when the sump temperature drops below the safe operation line
shown in
Figure 27
for more than 10 seconds.
Figure 25: Bottom shell temperature
NOTE:
Operation in this refrigerant dilution area is safe in air-to-air heat pump heating
mode. For other applications, such as AC only, review expansion device to raise
superheat. A cold sump may result in high refrigerant migration after shutdown.
If an accumulator has to be used, the oil-return orifice
should be from 1 to 1.4 mm in diameter for
models ZRD42K* to ZRD81K* and ZPD34K* to ZPD91K*, depending on compressor size and
compressor floodback results. Models ZRD94K*, ZRD125K* and ZPD103K* to ZPD182K*
should use an orifice diameter of 2.0 mm.
A large-area protective screen with mesh no finer than
30 x 30 (0.6 mm openings) is required to protect this small orifice from plugging with system
