8 C6.2.38/0719/E
The lower right boundary of the operating envelope is the minimum compression ratio required to keep
the scrolls loaded. Operation below this limit could
result in the compressor intermittently loading
and unloading and noisy operation.
Figure 6: R290 application envelope for YBVH* compressors with 10K suction superheat, 25-92 Hz
Please note some comments about the envelope:
▪ Before compressor start with the matched pair of YBVH* and the ED3 drive, the pressure
difference in the system has to be below 10 bar. If the pressure difference is reduced by opening
the expansion valve, care must be taken to avoid liquid flood back to the compressor – also see
oil dilution chart in Figure 5.
▪ An oil return test for the system must be performed. If required, the system design must be
improved to ensure sufficient oil return from the system to the compressor – also see Chapter
2.6.3 "Oil filling and oil level".
▪ The use of 1500 rpm for low condensing and high evaporating temperatures is possible as shown
in the envelope.
▪ The system should be able to bring the compressor to a point inside the envelope as fast as
possible at the start, and to keep the compressor running there. Running outside the envelope is
not allowed.
▪ At start-up the system should be able to bring the compressor to a point inside the envelope as
fast as possible and to keep the compressor running there. Running outside the envelope is not
allowed. Emerson’s recommendation is to start with a speed of 3000 rpm and to freeze the speed
for minimum 30 seconds or longer until the system is in stable operation – see Figure 7 "Ramp
up".
Figure 7: Ramp up and controlled shutdown
▪ Running/oscillating the compressor in and out of the envelope borders is not allowed and should
be avoided.
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