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

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

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

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

Heat Pump Cycle Cooling Mode 4-Way-Valve Vorteil: - einfach, da nur 2 Ventile - denkbar ist ein von RB erzeugtes Modul zum Heizen und Kühlen, in dem der Verdichter, der innere WÜ, das Expansionsventil und die beiden 4-Port-Ventile integriert sind

Heat Pump Cycle Heating Mode frost and ice formation flash fogging 4-Way-Valve flash fogging dust smoldering Vorteil: - einfach, da nur 2 Ventile - denkbar ist ein von RB erzeugtes Modul zum Heizen und Kühlen, in dem der Verdichter, der innere WÜ, das Expansionsventil und die beiden 4-Port-Ventile integriert sind temperature pressure HX: inversion of flow direction

Frost and ice formation

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

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

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

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

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

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

Advanced Heat Pump Cycle

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

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

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)

CO2 A/C-HP - System Cooling Mode engine Vorteil: - einfach, da nur 2 Ventile - denkbar ist ein von RB erzeugtes Modul zum Heizen und Kühlen, in dem der Verdichter, der innere WÜ, das Expansionsventil und die beiden 4-Port-Ventile integriert sind

CO2 A/C-HP - System Heating Mode engine Vorteil: - einfach, da nur 2 Ventile - denkbar ist ein von RB erzeugtes Modul zum Heizen und Kühlen, in dem der Verdichter, der innere WÜ, das Expansionsventil und die beiden 4-Port-Ventile integriert sind

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

heating mode (after 5 min) 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 + 4.2 K + 0,69 lt./100km + 7.3 K + 1.21 lt. (100%) heat pump + 7.3 K + 0.79 lt. (- 35%) Ansatz: Mehrverbrauch für el. Zuheizer linear hochgerechnet

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