B-COOL TST4-CT-2005-012394
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B-COOL
Number: TST4-CT-2005-012394
Acronym: B-COOL
Title: Low Cost and High Efficiency CO2 Mobile Air
Conditioning System for Lower Segment Cars
Final Report
Publishable Version
Report Version:
01
Report Preparation Date:
24.02.2009
Classification:
Publishable
Contract Start Date:
November, 30th, 2008
Duration:
42 Months
Project funded by the EU
Sixth Framework Program
Contract N°012394
B-COOL TST4-CT-2005-012394
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Document History
Version File Name
Author(s) Revised Approved
0.1
Strupp
Final_report_publishable.doc
Malvicino
Malvicino
Date
B-COOL TST4-CT-2005-012394
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DOCUMENT HISTORY ....................................................................................................... 2
1
INTRODUCTION .......................................................................................................... 4
2
R-744 AS A REFRIGERANT FOR MOBILE AIR CONDITIONING.............................. 5
3
TESTING PROCEDURES ............................................................................................ 6
3.1
3.2
4
BASELINE VEHICLE CHARACTERISTICS ................................................................ 8
4.1
4.2
5
FIAT PANDA:....................................................................................................................................... 8
FORD KA: ........................................................................................................................................... 8
R-744 SYSTEM ARCHITECTURE ............................................................................... 8
5.1
5.2
6
FUEL CONSUMPTION ........................................................................................................................... 6
COOL DOWN ....................................................................................................................................... 7
THE FIAT PANDA B-COOL SYSTEM .............................................................................................. 9
THE FORD KA B-COOL SYSTEM ................................................................................................... 9
SYSTEM PERFORMANCE ........................................................................................ 10
6.1
6.2
FUEL CONSUMPTION ......................................................................................................................... 10
COOL DOWN ..................................................................................................................................... 11
7
LCCP - LIFE CYCLE CLIMATE PERFORMANCE .................................................... 11
8
ON BOARD SAFETY ................................................................................................. 13
9
NVH ............................................................................................................................ 14
10 LEAK RATE AND SYSTEM RELIABILITY ................................................................ 15
11 COST ANALYSIS....................................................................................................... 15
12 CONCLUSIONS ......................................................................................................... 16
REFERENCES .................................................................................................................. 17
B-COOL TST4-CT-2005-012394
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1 Introduction
The B-COOL Project was fully devoted to the development of a low cost and high
efficiency air-conditioning system based on a vapor compression cycle using CO2 identified with the acronym R-744 when used as refrigerant fluid.
Methods to assess performance, fuel annual consumption and environmental impact were
identified, within the Project, and constituted a first step towards EU new standards.
The EU, as Greenhouse Gas emission reduction measure, proposed the ban for Mobile
Air Conditioning systems of fluids having a Global Warming Potential higher than 150 (i.e.
R134a) with possible future complementary measures - e.g. measurement of the MAC
fuel consumption – and this initiative represents a challenge and an opportunity for OEMs
and Mobile A/C Suppliers to increase their competitiveness.
R-744 is one promising candidate to
replace the present used fluid, named
R134a. Besides safety, reliability and
efficiency, the additional cost, estimated
in the range of 70 - 150 Euro with
reference to the low priced car systems,
represents a serious challenge to its
diffusion.
This is even more relevant considering
the lower priced cars that constitute up
to 80% of the present EU car market
considering the recent EU enlargement.
The Project has been carried out by a
consortium constituted by 2 major
Figure 1 - The B-COOL consortium
OEMs,
4
suppliers
and
three
acknowledged
excellence
centers
gathering skilled European scientists and engineers in this specific field.
The project has been focused, at first, to the identification of the most appropriate testing
procedures so to be able to qualify in realistic way a mobile air conditioning in terms of fuel
consumption and performances (thermal comfort). A specific activity has also been
launched to verify the safety-related issues.
The major effort has been devoted to the development of the A/C systems for a Fiat Panda
with automatic air conditioning and a Ford KA with manual control.
The cars have been fully characterized following the identified procedures before and after
the R-744 A/C system installation.
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2 R-744 as a refrigerant for mobile air conditioning
Compared to conventional refrigerants, the most remarkable property of R-744 is the low
critical temperature of 31.1°C, so a vapour compression cycle operating at normal ambient
temperatures works close to and even above the critical pressure of 7.38 MPa. This leads
to three distinct features of R-744 systems:
 Heat is rejected at supercritical pressure in many situations. The system will then use a
transcritical cycle that operates partly below and partly above the critical pressure. Highside pressure in a transcritical system is determined by refrigerant charge or the
expansion device and not by saturation pressure. The system design thus has to
consider the need for controlling high-side pressure to ensure optimized COP and
sufficient cooling capacity.
 The pressure level in the system is high (around 3-10 MPa). Components therefore
have to be redesigned to fit the properties of R-744. Due to smaller volumes of piping
and components, the stored explosion energy in a R-744 system is equal to a
conventional system. A benefit of high pressure is that the required compressor
displacement is reduced by 80-90% for a given cooling capacity. Compressor pressure
ratios are low, thus giving favourable conditions for high compressor efficiency.
2=3
4=5
2=3
4
Condenser
Gas Cooler
Compressor
1
IHX
Expansion Valve
5
Compressor
Evaporator
Expansion Valve
6
Evaporator
7=8=1
6
Fig. 0: Simple diagram of R134a
MAC system.
R-134a loop
7=8
Fig. 0: Simple diagram of R744 MAC
system.
R-744 loop
Large temperature variation glide
occurs during heat rejection. At
supercritical
or
near-critical
pressure, all or most of the heat
transfer from the refrigerant takes
place by cooling the compressed
gas without phase change. The heat
exchanger is therefore called gas
cooler instead of condenser. Gliding
temperature can be useful in heat
pumps for heating water or air. With
proper heat exchanger design the
refrigerant can be cooled to a few
degrees above the entering coolant
(air, water) temperature, and this
contributes to high COP of the
system.
Figure 2 - R-744 and R-134a systems
schemes. The Internal Heat Exchanger is
adopted to assure appropriate efficiency to the
R-744
loopdifference of R-744 thermo-physical properties and cycle characteristics
Due
to the
compared to HFC refrigerants, typical efficiency curves (COP, Coefficient Of Performance:
cooling capacity divided by power input) show different trends with different ambient
temperatures.
R-744 tends to be more efficient at lower ambient temperatures, while HFC systems may
be slightly more efficient at higher ambient temperatures. This tendency has been verified
for a variety of applications such as mobile air-conditioning and supermarket refrigeration.
The intersection of the two depicted curves varies depending on various factors such as
cycle layout and component efficiency.
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It shall be emphasized that in this situation, it
would be misleading to base the comparison
indicated in Figure 3 on design-point
conditions, which typically are at an extreme
ambient temperature. A more sensible basis
for comparison is to use mean/average
conditions, or to apply a seasonal analysis
based on climatic variation, as applied in
LCCP (Life Cycle Climate Performance)
calculations.
Figure 3 - COP of R-744 and R-134a
systems at varying ambient temperature
R-744 technology is widely diffused for low
temperature refrigeration and start to be
applied as heat pump and air conditioner [1].
a) Heat pumps and Air Conditioning: Heat pump water heaters, heat pumps for tap water
heating, were commercialized in Japan in 2001 for both residential and commercial
applications. Systems adapted to European conditions are under development. One of the
major advantages is that these transcritical systems are able to provide water at high
temperatures (90 °C) without a substantial drop in COP, compared to systems using HFC
as a refrigerant.
b) Commercial refrigeration: R-744 is an important refrigerant alternative to HFCs in
commercial refrigeration systems. Some of the major companies have introduced direct
systems using solely R-744 as a refrigerant with sub/transcritical cycles, depending on
ambient temperature. Also in the light commercial sector, i.e. stand-alone equipment such
as bottle coolers and vending machines, some of the major companies have introduced R744 technology.
c) Mobile Air Conditioning: Mobile Air conditioning is the application with the largest HFC
emissions and the second largest GHG emissions in R-744-equivalent resulting from
refrigerant emissions. Hafner et al (2004) compared R-744 mobile air-conditioning systems
to R-134a and R-152a systems based on experimental and climate data from different
cities around the world. Compared to HFC-134a R-744 showed an LCCP reduced
by 18 – 48 %.
3 Testing procedures
3.1 Fuel consumption
The procedure has been conceived to be feasible in the existing testing benches and to be
representative of a real use and has been derived from a study carried out by Armines and
CRF [2].
The procedure is based on a modified NEDC cycle (Normal European Driving Cycle)
where four elementary Urban Cycles have been added to evaluate the effect of the cooldown transient as well as of steady state conditions during the urban cycle (Figure 4).
The test can be performed in a climatic chamber equipped with rolling bench and does not
require major changes to the existing testing facilities and standard testing procedures.
B-COOL TST4-CT-2005-012394
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140
35
Outlet Temperature
Cabin Temperature
Speed
Temperature (°C)
30
Equivalent thermal conditions without
solar irradiation have been identified
under the hypothesis that the solar
cabin soaking can be represented by an
air
temperature
increase.
This
hypothesis introduces an approximation
but simplifies in a crucial way the testing
procedure requirements making it
applicable in almost all the existing
facilities (climatic chamber with rolling
benches and emission and consumption
120
25
100
20
80
15
60
10
40
5
20
0
0
500
1000
Time (min)
1500
Speed (km/h)
To assure an acceptable accuracy level
each test has to be repeated at least
three times.
0
2000
Figure 4 – The testing cycle based on the
New European Driving Cycle (NEDC) that
has been
adopted
to assesssystems).
the fuel consumption of
measurement
mobile air conditioning systems.
The ambient testing conditions are as
follows:
70
T e m p e ra t u ra [° C
]
Temperature
(°C)
60
28°C and 50% R.H. - European Summer:
these conditions can be considered
representative to classify the air
conditioning system with regards to the
fuel consumption and thermal comfort.
The A/C system set point: 20°C.
50
30 km/h
40
60 km/h
90 km/h
IDLE
Head
30
20
Outlets
10
0
0
20
40
60
80
T e m p o [ m in ]
1 00
1 20
1 40
Time (min)
Figure 5 - Cool Down test (43°C - 35%
R.H., 900 W/m2 solar irradiation). The test
start when the air temperature at head level
reached 60°C. A/C is set at maximum
dehumidifier.
system set point:
powerThe
andA/C
in recirculation
mode 20 °C.
35°C and 60% R.H. - Severe Summer:
representative of very high thermal load
(non-European).
The A/C system set point: 23°C.
15°C and 70% R.H. - Dehumidification:
to consider the use of the A/C as a
All tests are performed with the A/C in fresh air mode
A specific procedure has been defined to represent in a realistic way the use of manual
A/C systems and thermal comfort [3].
3.2 Cool down
The test is devoted to qualify the air conditioning system in terms of cooling performance
under severe thermal load (see figure 4) and should be performed in a climatic wind tunnel
with solar irradiation simulation.
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4 Baseline vehicle characteristics
Two low segment cars have been selected
as baseline vehicles:
4.1 Fiat Panda:

1.2 l Gasoline with automatic A/C

COLOUR: black

COMPRESSOR: 60 cc scroll,

transmission ratio = 1.32
FIAT PANDA

Figure 6 – The Ford Ka and Fiat Panda
used to realize the B-COOL vehicle
CONDENSER: 574 x 315 x16
demonstrators
Serpentine Parallel Flow with integrated dryer

EVAPORATOR: 185 x 188 x 58, plates and Fins

EXPANSION DEVICE: thermostatic expansion valve

LINES: 3 lines
4.2 Ford Ka:

1.3 Gasoline with manual A/C (2005 my)

COLOUR: Black

COMPRESSOR: 90 cc scroll, transmission ratio = 1.40

CONDENSER: 400 x 382 x 20

EVAPORATOR: 210 x 240 x 81

EXPANSION DEVICE: orifice & accumulator

LINES: 4 lines
5 R-744 SYSTEM ARCHITECTURE
Both the developed R-744 systems have a
similar architecture (Figure 7) based on
variable displacement piston compressor,
internal heat exchanger and orifice
expansion device and an accumulator. The
compressors, of different type, are of piston
type with have 29 cc displacement modified
to have a maximum displacement of 20 cc.
GAS COOLER
HP SENSOR
LP SENSOR
INTERNAL
HEAT EXCHANGER
CHARGE PORT
FILTER
COMPRESSOR
EVAPORATOR
x
ACCUMULATOR
ORIFICE
Figure 7 - B-COOL R-744 A/C system
scheme
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5.1 THE FIAT PANDA B-COOL SYSTEM
Two versions of R-744 system have been
conceived, one with a separate internal
heat exchanger (figure 8a) and one with
the heat exchanger integrated in the
accumulator (Figure 8b).
The components have been designed and
realized by Dephi, the line, the
accumulator and the internal heat
exchanger by Maflow. Sensata supplied
the temperature and pressure sensors.
The expansion device is a fixed orifice
(0.55 mm) with a bypass at 12 MPa
(Egheloff)
The evaporator fits in the HVAC module
not requiring major changes and the gas
cooler has the same face area of the
baseline condenser. The gas cooler fan,
that is located on the left hand in the
baseline system, has been moved in a
more central position for a more uniform
air flow.
5.2 THE FORD
SYSTEM
KA
EVAPORATOR
ORIFICE
INTERNAL
HEAT EXCHANGER
FILTER
ACCUMULATOR
GAS COOLER
VARIABLE DISPLACEMENT
28 cc COMPRESSOR
with reduced displacement to 15 cc
Figure 8a - First version of B-COOL Fiat
Panda R-744 system. The compressor
position, between the engine and the
firewall led to a characteristic design of the
Internal Heat Exchanger
ORIFICE
EVAPORATOR
FILTER
B-COOL
The Ford KA R-744 system has a more
conventional lay out due to the fact that
the compressor is located in front of the
engine. The components have been
designed and realized by Valeo, the A/C
lines and the internal heat exchanger by
VARIABLE DISPLACEMENT
28 cc COMPRESSOR
with reduced displacement to 15 cc
GAS COOLER
Figure 8b - Second version of B-COOL
Fiat Panda R-744 system: the internal
Heat Exchanger has been integrated in
the accumulator.
Maflow,
who
also
provided
accumulator;
Sensata
supplied
temperature and pressure sensors.
ORIFICE
INTERNAL
HEAT EXCHANGER
ACCUMULATOR
GAS COOLER
Figure 9 - Ford KA B-COOL R-744 A/C
system
the
the
The expansion device is a fixed orifice
(0.50 mm) with a bypass at 12.5 MPa. The
heat exchangers have the same face area
of the baseline components. The
accumulator
replaces
the
R134a
accumulator of the baseline system. The
co-axial tube internal heat exchanger is
designed as a separate component. The
gas cooler size is severely limited by the
front-end package.
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6 System Performance
The demonstrator vehicles have been
characterized following the procedure
above described before and after the
installation of the R-744 systems.
Testing Conditions
Temperature
Humidity
Air Enthalpy
Panda - R-134a
6.1 Fuel consumption
Panda - R-744 1st
The measured data are reported in
the tables 1 and 2. The results of the
two versions of the Panda system
have been included to show the effect
of the system changes (compressor
displacement increase from 15 cc to
20 cc and adoption of the IHX).
Panda - R-744 2nd
Ka - R-134a
Ka - R-744
38
38
45
65
70
100
112
126
100
109
The Fiat Panda R-744 1st version
system shows also a slightly
decrease of the thermal comfort at 35
°C that is fully recovered with the
second version of the system. The
Ford Ka has a better performance at
35 °C due to the evaporator
temperature control, the baseline
produced a bit too low outlet
temperature. The lower increase, in
percent, of the fuel consumption of
the Ford Ka with respect to the
reference test point (baseline @ 28
°C) to is due to the quite high baseline
Testing Conditions
Temperature
Humidity
Air Enthalpy
Panda - R134a
Panda - R-744 1st
Panda - R-744 2nd
Ka R134a
Ka - R744
15 °C
28 °C
35 °C
70% R.H.
50% R.H.
60% R.H.
34 J/kg
59 J/kg
91 J/kg
Themal Comfort [1-10 scale]
n.a.
n.a.
n.a.
n.a.
n.a.
8.1
8.1
8.1
8.2
8.5
A/C system
value,
35 °C - 60% R.H.
2.5
2.0
1.5
15 °C - 70% R.H.
1.0
28 °C - 50% R.U
0.5
Panda - R-744 1st
0.0
30
40
50
60
70
80
7.3
7.3
7.7
7.3
7.8
Table 2: Thermal comfort in arbitrary units
measured on a NEDC based testing cycle
3.0
Panda - R-134a
Panda - R-744 2nd
177
180
225
135
143
Table 1: measured fuel overconsumption
on a NEDC based testing cycle - % of the
baseline
system
(R-134a)
fuel
overconsumption at 28 °C 50% R.H. – Note
that the baseline Ford Ka fuel consumption
is rather higher than the Fiat Panda baseline
fuel consumption.
Both the R-744 systems shows a
slightly higher fuel consumption at
higher thermal load (35 °C).
Fuel Add. Cons. [l/100 km]
15 °C
28 °C
35 °C
70% R.H.
50% R.H.
60% R.H.
34 J/kg
59 J/kg
91 J/kg
Fuel Overcunsumption
[% of baseline @ 28 °C]
90
100
Ambient Conditions (H - kJ/kg)
Figure 10 - Fiat Panda fuel consumption increase
due to the air conditioning vs ambient air enthalpy.
The data have been used as input for the LCCP.
fuel
consumption
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6.2 Cool down
The Table 3 synthesizes the results of
T Outlet Mean [°C]
the cool down test comparing the
10'
30'
60'
90'
120'
baseline vehicles with the R-744 A/C
Panda - R134a
9.9
9.3
7.4
10.6
16.9
system equipped demonstrators. The
Panda - R744 1st
10.4
5.4
4.9
7.1
14.3
results shows that the R-744 system are
Panda - R744 2nd
8.0
7.0
7.0
5.0
9.0
Ka R134a
able to guarantee adequate cooling
14.0
9.0
7.0
7.0
17.5
Ka - R744
12.0
5.0
5.0
5.0
19.0
performance event at high thermal load
and the second version of the Panda
system with increased compressor Table 3: cool down test cycle at 43 °C, 30%
displacement allows to achieve better R.H. and 800 W/m2. – see figure 4
performance at the end of the cycle (idling). It should be highlighted that this increase of
cooling power is paid with a fuel consumption increase (see table 1 and figure 10).
Two approaches [4] have been applied
within B-COOL to estimate the LCCP of a
mobile air conditioning system:
bench data: where the analysis is based
on theoretical vehicle models, with typical
engine efficiencies. The defined thermal
load (f{tambient}) of the vehicle(s) and
the corresponding cooling demand is the
basis for performance tests carried out in
test benches as shown in figure 11.
vehicle data: the analysis is based on
measured fuel consumption as function
of ambient temperatures (figure 10),
which can be applied for various
climates.
Required compressor shaft power [W]
7 LCCP - LIFE CYCLE CLIMATE PERFORMANCE
2500
2000
HFC
R74 4
1500
1000
500
0
10
20
30
40
Ambient temperature [°C]
50
Figure 11 - Bench test data (@ equal
cooling capacities) used as input for LCCP
calculation for Ford Ka
The LCCP estimation in table 4 has been performed considering that:
 the materials are from the same region (e.g. Al from North Europe) and assembled in
the same plant (e.g. France), this implies that 1 kg of CO2 is emitted for each kg of and
the installed A/C system.
 Entire life time HFC-loss are estimated as equal to 0.4 - 0.65 kg, including 15-25% loss
during service (1x in central & northern EU; 2x in southern EU) and 50% recovery at
End of Life (EoL).
 Service is assumed to be requested after 150g HFC loss in S-EU and 180g in C&N-EU.
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Both the calculation methods have been applied:
 using the vehicle data (Fig. 10) for the Fiat Panda
 using the test bench data for the Ford KA (Fig. 11)
The LCCP calculation has been performed considering three different climate regions:
Athens, Paris and Trondheim.
The results of the analysis are reported
in table 4. There is evidence that the R744 system has a lower LCCP in all the
three evaluated conditions. Even at
higher fuel consumptions of the R-744
system at an improved thermal comfort,
the reasonable HFC-leakage rates
results in higher LCCP values for the R134a systems. In addition to that the
data in the table also show that both the
adopted LCCP calculation approaches
confirm the ranking between the two
systems.
Fuel consumption
measured on-board
Fiat Panda R134a
Fiat Panda R-744
Fiat Panda R- 744 2nd*
Life Time Emissions
Athens
Paris
Trondheim
kg CO2/ 12Years
2871
1244
906
1968
654
310
2535
846
377
*@ higher thermal comfort
Table 4:a
LCCP (Life Cycle Climate
Performance) estimation for R-134a and R744 B-COOL systems tested on board (see
figure 9).
Fuel consumption
measured on bench
Ford Ka R-134a
Life Time Emissions
Athens
Paris
Trondheim
kg CO2/ 12Years
2814
1217
872
1638
552
275
Ford Ka R-744
It should be underlined that, when bench
test data are used as input, the Table 4:b LCCP estimation for R-134a and
procedure risks to underestimate the R-744 B-COOL systems tested at bench
LCCP value, as the tables show: the (see figure 10).
Fiat Panda MAC system has significant
lower fuel consumption than the Ford Ka system when measured on board. To estimate
accurately the effect of vehicle fuel consumption of the MAC during a driving cycle when
bench data are use as input a sophisticated and well tuned vehicle model is required. The
system bench test cannot take into account the effect of on board installation.
The use of on board measurements allows obtaining a more reliable value of the LCCP
value.
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8 On board safety
In the framework of the B-COOL
project, tests and theoretical analysis
have been performed to assess the risk
associated to the R-744 leak in the
cabin so to evaluate if safety devices
are required.
C head
C mean
6
5
4
3
2
1
0
0
1000
2000
3000
4000
t (s)
Figure 12 - R-744 concentration at driver
place with 4 passengers, maximum
ventilation, re-circulation. Sudden leak: all the
charge is released in 60 s. maximum leak
C Feet
C head
C mean
18
16
14
C (% vol.)
The R-744 A/C system has an internal
volume of around 1.2 l to 1.4 l with a
charge in the range of 350 g. The
empty cabin volume of a B-segment
car is around 2.1 m³.
C Feet
7
C (% vol.)
R-744 is a non-toxic refrigerant (as
classified in EN 378), however at
concentration equal or higher than 3%
vol. it causes stimulating effect on the
respiratory centre and could be lethal
at concentration higher than 9% vol.
12
10
The highest peak R-744 concentration
8
6
is theoretically reached when the entire
4
refrigerant of the A/C system is
2
0
discharged in the cabin and 4
0
1000
2000
3000
4000
5000
6000
7000
passengers are on board (air volume
t (s)
reduction of 200 l approx. and the R744 emission due to the respiration).
Figure 13 - R-744 concentration at driver
These unrealistic conditions lead to a
place with 4 passengers, no ventilation, remaximum peak concentration of 12%
circulation. Sudden leak: all the charge is
vol. R-744 and temperature controlled
released in 60 s.
has been used to simulate the A/C
system leak in a Fiat panda cabin. The
R-744 concentration is measured by means of sensors (accuracy ± 20 ppm in the range of
0-10000 ppm) placed at the driver and back passenger places at breath and at feet level.
A test matrix has been followed considering different leak rate, ventilation level,
recirculation and passenger presence. The air outlet has been oriented to the driver’s
head, and the vents at the front passenger seat are closed so to increase the R-744
concentration at the driver’s head.
On the basis of literature data and tests it has been found that the R-744 concentration
increase due to the passenger presence can be estimated in:
0.5 %vol./passenger: recirculation and no ventilation
0.1 %vol./passenger: recirculation and max ventilation
B-COOL TST4-CT-2005-012394
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The tests represent worst-case scenarios
with the highest pressure in the evaporator
and the front panel outlets oriented to the
face of the occupant.
The tests results show that the most critical
cases are:

leak in recirculation mode and no
ventilation

sudden leak in recirculation mode and
full ventilation
and indicate that the risks due to the R-744
release in the cabin can be prevented
safely by:
Figure 14 - Two mini-sheds used to
evaluate the system tightness in the
ARMINES-CEP laboratory

managing properly the recirculation flap

detecting critical leak by means of conventional diagnostic tools (e.g. pressure and
temperature sensor monitoring), so no additional sensors are strictly required
In addition to that, it is important to remark that:

If the leak happens when the engine and/or the electrical systems are OFF (e.g.
parking) sensors or other active devices are useless because not active and R-744
concentration drops rapidly to non critical values just when the door is open

If the leak happens when the engine and/or the electrical systems are ON a critical
leak can be detected elaborating properly the signal of pressure and temperature
sensors and the information available on the vehicle network. The activation of fresh
air mode and ventilation can prevent any risk.
9 NVH
The noise and vibration may represent an issue for the R-744 systems. The compressor is
the main source, while the lines are another risky element. The B-COOL system has
shown limited problems related to NVH. The NVH level is aligned with the baseline vehicle
characteristics. In general several options can be considered and are still under study to
decrease the negative NVH characteristics:
 optimized compressor
 non-corrugated flexible lines.
 sound insulation and vibration damping material.
 mufflers.
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10 Leak rate and system reliability
This issue has been one of the most common in the history of R-744 MAC systems, and
also is important within the context of the B-COOL Project. The leakage rate needs to be
kept under control so that the system only needs to be serviced within the specified
timeframe, while offering good performance.
If a component leaks out of the specified rate, the system will loose its charge and will stop
working, requiring a refill. The most critical issue is the leakage through the compressor
shaft seal.
Other sources of leaks are the seals and fittings, but metallic seals and good tightening of
the fittings are to be used to keep the leakage within specifications.
The B-COOL system leak rate has been measured adopting the concept first developed
for the measurement of leak rate of A/C systems running with R-134a [5] and based on the
measure of the R-744 concentration in an accumulation volume named mini-shed.
The measured leak rate was not acceptable, indicating that further improvements are
required to reach an annual leak rate of about 50g/year that can be considered a
reasonable target maintenance/recharge.
11 Cost analysis
The B-COOL project included the prediction of system cost with a very ambitious target of
an additional cost of 30 Euro/system.
In order to insure the coherency of cost estimates and to have a common baseline the cost
estimation has been performed with the following main assumptions

the given costs are the ones paid by the car manufacturers which means prices for the
suppliers

as reference an average R-134a system cost has been identified on the basis of the
Fiat Panda and Ford KA A/C loops
and components. The present cost
has been reduced according to the
R-134a
R-744
(reference) Min (%) Max (%)
market trend to estimate the cost in
Compressor
1
1.3
1.7
2011

the electronic control has been
excluded

the reference year is 2011 for R744 production

production volume assumption is
300.000 units/year for all the
components except gas cooler and
evaporator where the selected
Evaporator
Condenser/Gas Cooler
Lines, Accumulator, IHX
Refrigerant
Sensors
Expansion Device
Total
1
1
1
1
1
1
1.5
0.8
2.8
0.3
1.0
1.3
1.8
1.1
3.1
0.3
1.2
1.6
1.5
1.8
Table 5: cost range of a R-744 A/C system,
relative to a 2011 R-134a A/C system
(unitary cost).
B-COOL TST4-CT-2005-012394
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volumes considered are the full production capacity (i.e. 1.4 million units/year).
As synthesized in the table 6, the cost of a 2011 R-744 A/C system ranges from 1.5 to 2
times the cost of a 2011 R-134a loop (e.g. +100 Euro – +150 Euro).
This estimation is far from the original B-COOL target of an additional cost +30 Euro or in
other words a target of 1.2 times the cost of a 2011 R-134a A/C loop. Unfortunately, for
first applications in 2011 on small cars, it seems very hard to reduce the today’s given
figures in a significant way.
12 CONCLUSIONS
Within the B-COOL EU-funded project a R-744 air conditioning system has been
conceived, developed and installed on two vehicle demonstrators representative of the
European A-B segment: a Fiat Panda and a Ford Ka.
The R-744 air conditioning systems have been fully characterized on bench and on board
and compared with the baseline R-134a systems.
The results demonstrate that the performance issues have been solved and R-744 A/C
system can achieve the same efficiency level of present R-134a systems, even if further
developments and testing are required to reach the same reliability levels as with R134a
systems.
The system efficiency will increase when right-sized compressors will be available. The
28cc externally controlled variable capacity compressors, designed for C-segment cars,
when used on small cars, as in this study, in partial load, have a lower efficiency. Those
compressors can be used to validate the rest of the components, and in a first phase of R744 system diffusion, but smaller displacement compressors (15 cc) guarantee better
efficiency.
As it has been previously mentioned, on the short term the cost will be significantly higher
than present R-134a.
If all the OEMs were to switch to R-744 technology and production volumes were increase,
the cost would likely decrease but would hardly reach the same level of R-134a system.
The technical developments within the B-COOL Project have led to specific solutions for
the use of this technology in small cars.
The B-COOL project demonstrated that the R-744 technology for A-B segment cars seems
technologically affordable even if reliability and system additional cost are still open issues
that need to be further investigated.
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REFERENCES
[1] www.R744.com
[2] Méthode de mesure et mesures des surconsommations de climatisations automobiles - Convention
ADEME 01 66 067 - RAPPORT FINAL Référence ARMINES 20152 - Jugurtha BENOUALI, Denis CLODIC
(ARMINES), C. MALVICINO, S. MOLA (CRF)
[3] Mobile air conditioning fuel consumption & thermal comfort assessment procedure, C. Malvicino (a), S.
Mola (a), D. Clodic(b) - (a) Centro Ricerche Fiat, (b) Ecole des Mines de Paris, Center for Energy and
Processes. IIR Gustav Lorentzen Conference on Natural Working Fluids, Trondheim, Norway, May 28-31,
2006
[4] Global environmental &economic benefits of introducing R-744 mobile air conditioning, Armin Hafner &
Petter Nekså, SINTEF Energy Research Trondheim,, Norway, 2nd International Workshop on Mobile Air
Conditioning and Auxiliary Systems. Turin, Italy, November 2007
[5] Measurement of Leak Flow Rates of Mobile Air Conditioning (MAC) Components - How to Reach a
Generic Approach, SAE 2007-01-1186, SAE 2007 World Congress, Yingzhong Yu, Denis Clodic, Ecole des
Mines de Paris, Center for Energy and Processes