Results from CO 2 heat pump applications Ullrich Hesse, Zexel Valeo Compressor Europe GmbH

Contents q CO 2 as working fluid for heat pump q Air as heat source q Frost and ice formation q Advanced heat pump cycle q Conclusion

CO 2 Working Fluid for Heat Pump  properties of CO 2 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

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

4-Way-Valve Heat Pump Cycle

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

Frost and ice formation

q air to air cycle q investigation of outside HX icing at temperatures above freezing CO 2 heat pump test vehicle Icing Tests

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

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

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

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

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

Advanced Heat Pump Cycle

 concept of cycle  some results CO 2 heat pump test vehicle Advanced Heat Pump Cycle

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: % reduction of fuel consumption  no additional CO 2 heat exchanger in HVAC  packaging and risk for leakage

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)

CO 2 A/C-HP - System engine

CO 2 A/C-HP - System engine

gas cooler water CO 2 HX A/C mode (after 30 min) windtunnel 40 °C

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

Heating Performance

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

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