Results from CO 2 heat pump applications

1. Results from CO2 heat pump applications Ullrich Hesse, Zexel Valeo Compressor Europe GmbH

2. Contents • CO2 as working fluid for heat pump • Air as heat source • Frost and ice formation • Advanced heat pump cycle • Conclusion

3. CO2 Working Fluid for Heat Pump • properties of CO2 are advantageous for heat pump mode - high pressure level • fuel efficient cars need an efficient supplementary heater - heat pump • high performance of heat pump with engine coolant as heat source has been demonstrated

4. Air as Heat Source • costs: air to air system appears to be lowest cost heat pump cycle • performance: OK as supplementary heater, less capacity than than engine coolant as heat source => difficult for stand alone heating • problem: certain points need investigation

5. 4-Way-Valve Cooling Mode Heat Pump Cycle

6. 4-Way-Valve Heating Mode Heat Pump Cycle frost and ice formation flash fogging dust smoldering temperature pressure HX: inversion of flow direction

7. Frost and ice formation

8. air to air cycle investigation of outside HX icing at temperatures above freezing Icing Tests CO2 heat pump test vehicle

9. Icing Test 1 - Conditions • ca. 10 °C ambient • low humidity • idle • defrost

10. Idle Icing Test 1 - Defrost Temperature • ca. 10 °C • no HX blocking

11. Icing Test 2 - Conditions • Tests at more critical conditions: • 3 .. 5 °C ambient temperature • high humidity • wet road conditions • spray and mist from other cars driving on wet road of proving ground

12. 50km/h Idle Icing Test 2 - Defrost Temperature • HX blocked after 10 min

14. Conclusion on Icing • At critical conditions icing blocks air flow through outside HX after about 10 minutes • significant drop of performance • recovery when recirculation of air from engine compartment in idle • forced defrost necessary, e.g. cycle reverse

15. Advanced Heat Pump Cycle

16. concept of cycle some results Advanced Heat Pump Cycle CO2 heat pump test vehicle

17. Tasks for Concept of Cycle (1) • guarantied omission of flash fogging • known already from earlier R134a heat pump tests • safety related - most urgent problem • integration into vehicle thermal management • engine thermal management: 3 .. 5 % reduction of fuel consumption • no additional CO2 heat exchanger in HVAC • packaging and risk for leakage

18. Tasks for Concept of Cycle (2) • high performance • no performance limitation due to pressure limit • one flow direction through HX • secured oil return • easy separation of evaporator by check valve • omission of dust smoldering • may cause health problems (like in residential heaters)

19. engine Cooling Mode CO2 A/C-HP - System

20. engine Heating Mode CO2 A/C-HP - System

21. water CO2 HX gas cooler windtunnel 40 °C A/C mode (after 30 min)

22. windtunnel -20 °C heating mode (after 5 min)

23. Heating Performance

24. Fuel Consumption -20 °C, after 30 min., 50 km/h effect on head fuel temp. consumption el. heater + 4.2 K + 0,69 lt./100km+ 7.3 K + 1.21 lt. (100%) heat pump + 7.3 K + 0.79 lt. (- 35%)

25. Conclusion • Cycle with no risk of flash fogging • Improved heating performance • Low fuel consumption • Integration into engine thermal management • Reduced gas cooler load