B-COOL TST4-CT-2005-0123941/17

B-COOLNumber: TST4-CT-2005-012394Acronym: B-COOLTitle: 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 EUSixth Framework Program

Contract N°012394

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Document HistoryVersion File Name Author(s) Revised Approved Date0.1 Final_report_publishable.doc Strupp Malvicino Malvicino

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DOCUMENT HISTORY........................................................................................................21 INTRODUCTION...........................................................................................................42 R-744 AS A REFRIGERANT FOR MOBILE AIR CONDITIONING..............................53 TESTING PROCEDURES............................................................................................6

3.1 FUEL CONSUMPTION.......................................................................................................................... 63.2 COOL DOWN...................................................................................................................................... 7

4 BASELINE VEHICLE CHARACTERISTICS................................................................84.1 FIAT PANDA:..................................................................................................................................... 84.2 FORD KA:......................................................................................................................................... 8

5 R-744 SYSTEM ARCHITECTURE...............................................................................85.1 THE FIAT PANDA B-COOL SYSTEM.............................................................................................95.2 THE FORD KA B-COOL SYSTEM..................................................................................................9

6 SYSTEM PERFORMANCE........................................................................................106.1 FUEL CONSUMPTION........................................................................................................................106.2 COOL DOWN.................................................................................................................................... 11

7 LCCP - LIFE CYCLE CLIMATE PERFORMANCE....................................................118 ON BOARD SAFETY.................................................................................................139 NVH............................................................................................................................ 1410 LEAK RATE AND SYSTEM RELIABILITY................................................................1511 COST ANALYSIS.......................................................................................................1512 CONCLUSIONS..........................................................................................................16REFERENCES...................................................................................................................17

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1 IntroductionThe 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 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 conditioningCompared 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. High-side 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.

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.

Due to the difference of R-744 thermo-physical properties and cycle characteristics 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.

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 R-744 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 procedures3.1 Fuel consumptionThe 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 cool-down 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.

To assure an acceptable accuracy level each test has to be repeated at least three times.

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

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(climatic chamber with rolling benches and emission and consumption measurement systems).

The ambient testing conditions are as follows:

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.

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 dehumidifier. The A/C system set point: 20 °C.

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 characteristicsTwo 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

CONDENSER: 574 x 315 x16 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 ARCHITECTUREBoth 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.

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5.1 THE FIAT PANDA B-COOL SYSTEMTwo 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 KA B-COOL SYSTEMThe 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 Maflow, who also provided the accumulator; Sensata supplied the temperature and pressure sensors.

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 PerformanceThe demonstrator vehicles have been characterized following the procedure above described before and after the installation of the R-744 systems.

6.1 Fuel consumption 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).

Both the R-744 systems shows a slightly higher fuel consumption at higher thermal load (35 °C).

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 A/C system fuel consumption value,

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6.2 Cool down The Table 3 synthesizes the results of the cool down test comparing the baseline vehicles with the R-744 A/C system equipped demonstrators. The results shows that the R-744 system are able to guarantee adequate cooling performance event at high thermal load and the second version of the Panda system with increased compressor displacement allows to achieve better 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).

7 LCCP - LIFE CYCLE CLIMATE PERFORMANCETwo 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.

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 R-744 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 R-134a 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.

It should be underlined that, when bench test data are used as input, the procedure risks to underestimate the LCCP value, as the tables show: the 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 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.

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.

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.

The highest peak R-744 concentration is theoretically reached when the entire refrigerant of the A/C system is discharged in the cabin and 4 passengers are on board (air volume reduction of 200 l approx. and the R-744 emission due to the respiration). These unrealistic conditions lead to a maximum peak concentration of 12% vol. R-744 and temperature controlled 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

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:

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

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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 NVHThe 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.

10 Leak rate and system reliabilityThis 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.

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11 Cost analysisThe 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 market trend to estimate the cost in 2011

the electronic control has been excluded

the reference year is 2011 for R-744 production

production volume assumption is 300.000 units/year for all the components except gas cooler and evaporator where the selected 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 CONCLUSIONSWithin 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 R-

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744 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