1.
2.
1.
2.
3.
During customer unit test especially for oil management test, an oil level sensor or and oil sight glass at the lowest
safety level should be added into the test compressor, the install position refer to the picture. If oil level is above the
centerline in oil sight glass or oil level sensor doesn't trip compressor during oil return and oil loss risk
qualification
test in lab, then it means no oil loss risk in
field
where oil sight glass or oil level sensor is not installed for the
standard compressor.
CC-000199
35mm
NOTE:
The measurement is taken by considering the center of the oil sight glass or oil level sensor
Oil return test
Table 19: Oil return test
Test conditions
Pass criteria
Comments
Most un-favourable conditions for oil return are as be-
low:
Lowest refrigerant velocity and mass
flow
at low
Te and lowest speed for both cold start up test
and continuous running test
Highest refrigerant velocity and mass
flow
at high
Te and highest speed
For reversible unit, repeat test in both heating and
cooling mode
For advanced unit (Multiple exchangers roof top re-
heat coil, four-pipe chiller…) repeat test in all possible
configuration
Oil level must be above centerline or full in oil sight
glass
Compressor with oil level sensor, no oil level sensor
trip
If oil return test fails:
Check if potential oil trap in the system
Adjust oil management parameters to optimize
oil returning
Add additional oil or oil separator in the system
till oil is visible in the sight glass
Piping recommendations to ensure oil return
Oil return is highly linked to refrigerant velocity in pipes. The most unfavorable conditions for oil return are at
lowest refrigerant velocity corresponding to lowest evaporating T° and minimum compressor speed. Another most
unfavorable conditions for oil level safety are at high refrigerant velocity and mass
flow
corresponding to highest
evaporating T and maximum compressor speed, which means more oil quantity will take part in refrigerant cycle
while less oil is left inside compressor.
General recommendations are described in the
figures
below: To guaranty reliability, it is essential to fully qualify oil
return especially in most unfavourable conditions. Take particular care to units with reheat coil or multiple
exchangers.
Systems with reheat coils, multiple or split evaporator and/or condensers can be susceptible to oil logging. A means
to empty or pump out circuitry when not engaged should be implemented to prevent oil logging.
Scroll compressors, VCH115 | Application
© Danfoss | Climate Solutions | 2023.08
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