1.
2.
(1)
Only for DSH240 to DSH600.
(1)
Only for DSH240 to DSH600.
Cycle rate limit requirements
Danfoss requires a minimum compressor running time of 2 minutes to ensure proper oil return and sucient motor
cooling.
Additionally, compressor must not exceed 12 starts per hour. 12 starts per hour must not be considered as an
average, this is the maximum number of starts acceptable to keep a good regulation accuracy during low load.
Oil management logic recommendations
In some cases, oil management can be enhanced by control logic:
• If oil return test failed, a function can be integrated in control logic to run all compressors simultaneously during 2
minutes every hour in order to boost oil return. Time and delay can be ne-tuned by oil return test N°1 in section
Manage oil in the circuit. During oil boost, pay special attention to superheat management to avoid liquid ood
back.
• In trio system, after running long time in same state with 2 or 3 compressors, (1+2+3) or (1+2), (2+3) or (3+1), oil
unbalance may appears. A function can be implemented in control logic to stop all compressors during one
minute every two hours in order to balance oil. Time and sequence can be ne-tuned during Oil balancing test in
section Manage oil in the circuit.
Defrost logic recommendations / Reversible systems
In reversible systems, the defrost logic can be worked out to limit liquid ood back eect by:
Running full load during defrost to share liquid refrigerant between all compressors.
Reducing refrigerant ooding to compressor by transferring liquid refrigerant from one exchanger to the other
before reversing valve thanks to pressures.
The following defrost logic combines both advantages:
Figure 63: Defrost logic advantages
1
Cp 1 ON
Cp 2 ON
H
100%
2 65 8 973
4
CC-000019
4WV
EXV
© Danfoss | Climate Solutions | 2022.10 AB288965961751en-001402 | 57
Scroll compressors, DSH090 to DSH600 | Application
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