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

4-Way-Valve

Heat Pump Cycle

4-Way-Valve

Heat Pump Cycle

frost and ice formation

flashfogging

dustsmoldering

temperaturepressure

HX: inversion of flow direction

Frost and ice formation

air to air cycle

investigation of outside HX

icing

at temperatures above

freezing

CO2 heat pump

test vehicle

Icing Tests

Icing Test 1 - Conditions

ca. 10 °C ambient

low humidity idle defrost

ca. 10 °C no HX

blocking

Icing Test 1 - Defrost Temperature

0

20

40

60

0 10 20 30time [min]

tem

pe

ratu

re [

de

g.

C]

serial heater

stand alone air/airR744 heat pump

Idle

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

0

20

40

60

80

100

0 10 20 30 40 50

time [min]

tem

pe

ratu

re [

de

g. C

]

serial heater

stand alone air/airR744 heat pump

Icing Test 2 - Defrost Temperature

HX blocked after 10 min

50km/h Idle

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

concept of cycle

some results

CO2 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: 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

engine

CO2 A/C-HP - System

engine

gas cooler water CO2 HX

A/C mode (after 30 min)

windtunnel 40 °C

windtunnel -20 °C

heating mode (after 5 min)

Heating Performance

-20

0

20

40

0 10 20 30 40 50 60

time [min]

tem

pe

ratu

re [

°C]

head level - heatpump

head level -baseline50 km/h, 30 min

idle, 30 min

wind tunnel - 20 °C

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%)

Conclusion

Cycle with no risk of flash fogging

Improved heating performance

Low fuel consumption

Integration into engine thermal management

Reduced gas cooler load