Suction Line Accumulators - Emerson Copeland ZB12KCU Application Manuallines

▪ 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 floodback and oil dilution, all possible transient operation conditions
in the system 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, fans or pumps cycling at low load and more. To evaluate the risk of liquid floodback
and oil dilution, please refer to the chart in
The bottom shell temperature together with the evaporating temperature gives an indication whether
liquid refrigerant is returning or diluted in the compressor oil sump. The compressor sump
temperature must remain in the (green) safe area, as shown in the chart in Figure 13 below. In case
of operation in the (red) unsafe area, adjustments are required in order to modify the system design,
refrigerant charge or superheat setting of the expansion device(s). The bottom shell temperature
should be measured accurately. The thermo-probe must be properly insulated and positioned on the
opposite side of the sight glass or at an angle of 90° clockwise from the suction inlet with view on the
top.
Figure 13: Oil dilution chart (tb = bottom shell temperature; te = evaporating temperature) and oil temperature

3.16 Suction line accumulators

Due to Copeland scroll's inherent ability to handle liquid refrigerant, for example in flooded start and
defrost cycle operation, an accumulator is not required in most systems.
To determine if a suction line accumulator is required, the system designer must check this with an
appropriate test scenario. See section 3.15 "Compressor oil return, oil balancing, refrigerant
floodback and oil dilution tests".
If an accumulator is used, the oil-return orifice should be from 1 to 1.4 mm in diameter for all ZB*KCU
models depending on compressor size and compressor floodback results. To protect this small orifice
from plugging with system debris a large-area protective screen no finer than 30 x 30 mesh (0.6 mm
openings) is required. Tests have shown that a small screen with a fine mesh can easily become
plugged causing oil starvation to the compressor bearings. The size of the accumulator depends
upon the operating range of the system and the amount of sub-cooling and subsequent head
pressure allowed by the refrigerant control. For the correct selection and size of the suction line
accumulator, refer to the manufacturer's specifications.
AGL_Ref_ST_ZBKCU_EN_Rev01
Figure 13.
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