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R744, R152a and HFO-1234yf – Torino update |
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Experts discussed technical, environmental, safety and political issues of alternative refrigerants at the 2nd International Workshop on Mobile Air Conditioning in Torino last week.
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2007-12-04
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Around 170 experts from Asia, the EU and U.S. met in Torino, Italy, on 29-30 November, to shed light into the choice of refrigerant for next-generation Mobile Air Conditioning (MAC). Participants agreed that air conditioning has now become a key issue for carmakers to improve a vehicle's environmental performance, with Mr. Di Guisto from Fiat stating in his welcome address: "Mobile Air Conditioning is a very important and concrete tool to respond to climate change."
The contenders
The workshop presented existing and new refrigerant alternatives that could replace the current fluid HFC-134a in future cars. Besides CO2 (R744), speakers presented updates on HFC-152a and HFO-1234yf, another new fluid jointly developed by Honeywell and DuPont. The chemical companies emphasized that they do not support HFC-152a due to its flammability, but confirmed in their own presentation that HFO-1234yf would also be "mildly flammable". Therefore, under the ASHRAE designation for refrigerants HFO-1234yf would be classified as safety class A2 (lower toxicity, lower flammability), the same as R152a. Flammability tests are still under way. The companies did not, give details about the cost of the new refrigerant. HFO-1234yf is currently being evaluated by some manufacturers, including the Japanese carmakers (JAMA). Mr. Ikegami, speaking on behalf of JAMA, admitted, however, that long term toxicity tests for HFO-1234yf would not be finalized until end-2009.
The other alternative, R152, was subject of a presentation by Roberto Monforte from Fiat, which focused on the secondary loop of HFC-152 systems for small cars.
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Opening the workshop series, the U.S. Environmental Protection Agency (EPA) provided an update on safety requirements for HFC-152a and R744 in the United States. Early 2008, the EPA will organize a safety session on R744 under its SNAP (Significant New Alternatives Policy) approval.
William Hill from General Motors presented the GREEN-MAC-LCCP tool as a common methodology to assess different refrigerant options. Key to comparing alternatives in a consistent way is to gather the right data at the beginning of the evaluation process. R744.com will publish a separate article on the GREEN-MAC-LCCP tool soon to inform about its use, advantages and drawbacks.
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R744 on the agenda
Frank Wolf from OBRIST Engineering opened the series of presentations on the natural refrigerant CO2, highlighting emission reductions through R744. Summarizing global test results that show the higher efficiency of R744 compared to R134a, Wolf drew special attention to the future potential for further improvement through new system layouts for R744 MAC, including an ejector system and a compressor expander.
Armin Hafner from SINTEF Energy Research presented LCCP (Life Cycle Climate Performance) calculations comparing R744 MAC with current systems. According to this analysis, R744 outperforms R134a in all vehicle types and climate conditions, including the hot climates of China and India. Hafner concluded that, taking into account safety, performance and future improvement potential, CO2 is the most environmental and economically viable solution worldwide.
The joint presentation by Thomas Magnete, TLK-Thermo and the Institute for Thermodynamics Braunschweig (IfT) focused on a new family of R744 control valves for compressors to reduce fuel consumption. Test results proved a short response time of prototype valves, a low influence of the mounting orientation and a similar hysteresis of R744 and air as a reference medium. Mr. Strupp from the Technical University Braunschweig presented latest test results regarding R744 accumulator design and system modeling.
Klaus Martin from the VIRTUAL VEHICLE Competence Center (ViF) insisted that a more effective use of simulation tools will lead to significant cost savings in MAC development. If used in the early concept stage rather than in the late validation phase, simulation could be used for design and optimization. Martin stated that already available simulation tools deliver a high quality compared to actual measurements. ViF's presentation was supported by the leading suppliers ixetic, Egelhof and Modine.
Following latest test results by "Ecole des Mines de Paris", adding an ejector to a R744 refrigeration cycle will enhance the overall efficiency by 12%. In a second presentation, the French research institute analyzed the risk of being exposed too long to CO2 inside the car, which could happen if the recirculation mode is run constantly. A simple solution would be to add some outside air to the recirculation mode, according to Denis Clodic. This would solve the only safety issue associated with R744.
Valeo presented latest test results for CO2 MAC in small- and mid-sized cars. While R744 showed higher efficiency than R134a in mid-sized vehicles, Valeo experienced a lower efficiency of R744 in small cars. The use of an externally controlled compressor should reverse this tendency, the French company concludes.
Updating on the transition of R744.com towards a technical platform, Marc Chasserot from Shecco announced new services to be added to the website in 2008, including a technical forum, R744 Wiki and user-generated news.
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More information:
 OBRIST Engineering: Emission Reduction through MAC Innovation (952 KB)
SINTEF: Environmental & Economic Benefits of R744 MAC (740 KB)
IfT, TLK-Thermo, Thomas Magnete: Family of R744 control valves (1.7 MB)
IfT Braunschweig: R744 accumulator design and system modeling (8 MB)
ViF: Developing Refrigerant Cycles with Numerical Simulation (2.1 MB)
Shecco: R744.com - Towards a Technical Platform (921 KB)
› Other presentations will be available on the Workshop website soon
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