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European OEM tests CO2 MAC: 20% less fuel use |
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Latest tests with small size vehicles of a European, non-VDA carmaker have shown a dramatic increase in cooling performance for R744-based Mobile Air Conditioning, compared to a traditional R134a system. Furthermore, the CO2 system consumed up to 20% less fuel at high ambient temperatures.
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2008-04-22
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At high ambient temperatures of 35°C, generally defined as the point where R134a system show higher performance than R744 (CO2) systems, the use of CO2 can reach a 20% savings for the additional fuel consumption due to Mobile Air Conditioning (MAC), reducing it from 6.33 l/100 km to 6.05 l/100 km. Moreover, using R744 MAC results in a dramatically increased dynamic and cooling performance compared to traditional systems, as wind tunnel pull down tests at 45°C (40 kph driving cycle) have demonstrated.
These are key results of tests performed by Austrian R744 expert OBRIST Engineering on small size vehicles of a European carmaker, not member of the VDA (German Association of the Automotive Industry). Tests also showed that a significant potential for improvement of R744 systems is still at hand.
Test Conditions & Results
All tests were performed with a CO2 system comprising heat exchangers optimized in depth, a low pressure drop coaxial heat exchanger, a single accumulator, an externally controlled compressor, and an orifice with bypass function (FXV).
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Pull Down Test: The result of the 45°C wind tunnel pull down shows a significantly higher dynamic and cooling performance at the 40kph driving cycle for the R744 system and nearly constant vent outlet temperatures during the idle phase of the pull down. The higher performance of R744 MAC is a result of the slightly bigger compressor size, the optimized front end air flow and the use of the FXV for this test. Its performance benefit can be either used for a better system cool down or to reduce the system component size to have equal cooling performance with R134a. (see attached slides)
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Fuel Consumption Test: The same system setup was used to carry out New European Driving Cycle (NEDC) fuel consumption tests at three ambient temperatures: 35°C, 25°C and 20°C. The baseline fuel use of the vehicle in AC-OFF mode was determined beforehand with separate tests for the R744 and R134a system at 35°C. The final results show that the R744 system has a lower fuel consumption at the high and medium temperature and an equal fuel consumption at the 20°C test point. The decreasing efficiency benefit of the R744 system at lower ambient temperatures is a result of using a FXV. Replacing it by a pressure controlled valve (PXV) and optimizing the heat exchanger will result in significantly less fuel use at low temperatures, OBRIST expects.
Momentum for CO2 grows
After German carmakers had decided last September to use CO2 in vehicles before 2011, other European and non-European manufacturers are now also evaluating the performance of R744 MAC by applying best practice and testing state-of-the-art systems in different vehicle classes and climate conditions. Overall, the interest in CO2 MAC has significantly increased over the last two months, and more specifically since the Winter Meeting on Alternative Refrigerants last February, where leading German car manufacturers and suppliers confirmed that CO2 systems have reached a technical level to be ready for mass production.
Background
OBRIST Engineering focuses on the development of R744 systems and components for cooling and heating with a stronghold in the automotive market. Specialising on the conception, design, development, and testing of CO2 systems, the company today is a trusted partner for OEMs and suppliers all around the world.
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More information:
 OBRIST Engineering - Presentation April 2008 (85 KB)
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