1. CO2 CascadeComp_Studi Galileo  1 Semi-Hermetic Compressors for CO 2 Cascade Systems Hermann Renz Bitzer Kuehlmaschinenbau GmbH  Germany

2. CO2 CascadeComp_Studi Galileo  2 Semi-Hermetic Compressors for CO 2 Cascade Systems Contents  Introduction  Example of CO 2 cascade system  Properties of CO 2 vs. R22  Requirements on compressor design  Development Stages / Design Features  Summary

3. CO2 CascadeComp_Studi Galileo  3 Introduction Due to its environmentally benign characteristics and specific properties CO 2 has good potential for:  The extended use in subcritical cascade systems  like for example: Supermarket applications Industrial refrigeration systems  Specific features Very high volumetric cooling capacity Favourable TEWI, energy demand & installed cost Reasonable safety requirements

4. CO2 CascadeComp_Studi Galileo  4 Example of Supermarket Application – MT with HFC / LT with CO 2 Cascade

5. CO2 CascadeComp_Studi Galileo  5 Comparison of Properties – Low Temp CO 2 Cascade vs. R22 Compressor displacement counter- proportional to relative cooling capacities

6. CO2 CascadeComp_Studi Galileo  6 Pressure Ranges – CO 2 Cascade vs. R22 and R410A

7. CO2 CascadeComp_Studi Galileo  7 Requirements on Compressor Design  Consideration of CO 2 properties High Pressure levels  Strength of housing and crank gear High volumetric cooling capacity  Adaptation of displacement relative to motor power High vapour density / absolute mass flow  Adaptation of working valves & cross sections High gas solubility in oil  General requirements High isentropic efficiency Compact & solid design, use of “standard” parts

8. CO2 CascadeComp_Studi Galileo  8 Design Features  Pressure Levels  High pressure levels of CO 2 Compressor housing with high strength pressure  Safety factor “3“ acc. (pr)EN12693 Required pressures (approx.)  HP 40 bar  LP 25 bar (standstill pressure) Realised compressor construction  Compact design  Closed housing w/o bottom plate

9. CO2 CascadeComp_Studi Galileo  9  Adaptation of displacement Optimum match to “standard” motor sizes Potential for the use of “standard” parts  cost issue Smaller displacement allowing for generously sized crank gear Design Features Displacement / Crank Gear (1)

10. CO2 CascadeComp_Studi Galileo  10 Design Features Displacement / Crank Gear (2)  Adaptation of displacement by modified piston stroke Allowing for larger piston diameter  Potential for generously sized piston pin  and for special piston pin bearing Connecting rods with closed big end (large diameter) Potential for large cross sections of working valves  Adaptation to high vapour density  Improvement of compression process Reduced piston velocity Improved running smoothness

11. CO2 CascadeComp_Studi Galileo  11 Lubricant Issues with CO 2 Compressors Relevant to compressor  Heavy mechanical load on crank gear  High gas solubility in oil  Strong oil foaming tendency with pressure fluctuations High danger of boundary friction Relevant to (commercial) refrigerating systems  Oil return from system / avoiding strong oil migration and fouling effects in heat exchangers require: Good flow characteristics, low viscosity on suction side Sufficient miscibility with CO 2 Suitable Solution  e specially formulated POE lubricant

12. CO2 CascadeComp_Studi Galileo  12 Oil / Refrigerant (CO 2 ) Properties Vapour Pressure [bar] kin. viscosity [mm 2 /s] Temperature [°C]Concentration [M-% Oil in CO 2 ] Phase separation Temperature [°C]

13. CO2 CascadeComp_Studi Galileo  13 Compressor Lubrication  Enhanced centrifugal lubrication Quick oil supply after start Enlarged oil pocket at the shaft end Separation of oil foam by gravity principle Reduced oil carry over  minimum oil side flow Potential for oil monitoring system in oil pocket

14. CO2 CascadeComp_Studi Galileo  14 Summary  Convincing arguments for the application of CO 2 in low temperature cascade systems  Very high volumetric cooling capacity – allowing for: Small compressor displacement Small pipe sizes, favourable installed cost  High specific load on compressor housing and crank gear to be considered High pressure levels & vapour density  Need for Adapting compressor design and Lubrication system