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