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Scroll compressors, DSF090 to DSF530 | Application
• when the compressor is located at the coldest part of the installation, refrigerant vapor condenses in the
compressor.
• or directly in liquid-phase by gravity or pressure difference. When the compressor restarts, the refrigerant diluted
in the oil, or stored in evaporator, generates poor lubrication conditions, and may reduce bearings life time. In
extreme situations, this leads to liquid slugging that can damage the compressor scroll set.
Requirement
• Compressor can tolerate occasional flooded start, but it should remain exceptional situation and unit design must
prevent that this situation happen at each start.
• Right after start, liquid refrigerant must not flow massively to compressor
• The charge limit is a threshold beyond some protective measures must be taken to limit risk of liquid slugging and
extreme dilution at start.
System evaluation
Use the
Table 30: Charge limits for Single models
limits, in relation with the system charge and the application to quickly define necessary safeties to implement.
Table 28: System evaluation
Application
All
Non split
Split
Crankcase heater
The surface sump heater are designed to protect the compressor against off-cycle migration of refrigerant.
For DSF090-200, the surface sump heater is located on the compressor shell. For better standby energy
consumption, Danfoss provides 48W and 80W two optional surface sump heater. The selection of surface sump
heater could be refered to below principle:
Figure 54: DSF090 to 200
Table 29: surface sump selection principle
Compressor Surrounding Ambient
Unit has enclosure, no wind
Unit has no enclosure, with wind
Unit has no enclosure, wind >5m/s (ft/s)& ambient temperature <-5°C
For DSF270-530, the use of a 75W belt heater is recommended.
© Danfoss | Climate Solutions | 2023.06
and
BELOW charge limit
Ensure tightness between condenser & evaporator when system is OFF
• Thermostatic expansion Valve (TXV), Liquid Line Solenoid Valve LLSV strongly recommended
• Electronic expansion valve (EXV) must close when system stop including in power shut down situation
No test or additional safeties required
Since each installation is unique, refrigerant charge may vary
• Crankcase heater
• Liquid Line Solenoid Valve + pump-down cycle
Table 31: Charge limits for Tandem models
ABOVE charge limit
Surface Sump Heater
48W SSH
80W SSH
80W SSH + additional SSH/thermal insulation
in section Charge
• Crankcase heater
AB309735209512en-000603 | 47
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