The natural refrigerant CO
2 (R744) will not only lead to the lowest greenhouse gas emissions in Mobile Air Conditioning (MAC) in a European scenario, but will also outperform current and proposed refrigerants at the global scale. This is the result after real-life data for CO
2 had been entered into the latest agreed version of the GREEN-MAC LCCP model – a tool to calculate the life cycle climate performance of refrigerants in different world regions.
In the second version of the Alternative Refrigerant Cooperative Research Program (ARCRP), CO
2 leads to considerably lower emissions at relevant ambient temperatures below 35°C. Above this threshold, R134a is performing slightly better. Depending on the manufacturer and system used – from small to big, from simple system layout to complex ones - this point will range from temperatures in the high 20°C degrees to above 40°C, Frank Wolf, Vice President at Obrist Engineering, confirms.
Lack of transparency raises doubt
Already last year, members of the working group had raised doubts about the credibility of the tool after presentations had mostly shown R744 to perform less efficiently than R134a and later 1234yf. The tool’s complexity, and some might say its lack of transparency, had made it difficult to track how parameters were used to obtain certain results. To the knowledge of both Frank Wolf and Dr. Armin Hafner, Senior Scientist at SINTEF, the applied spreadsheets have never been shown to the public, with no independent 3rd party evaluation having taken place. Lately, experts had pointed to misleading and biased energy efficiency factors for 1234yf and badly engineered CO
2 systems as the cause for a surprisingly wide gap between the chemical and the natural refrigerant.
More importantly still, direct emissions scenarios assumed for R134a under the GREEN-MAC LCCP are not congruent with international findings. Already the International Panel on Climate Change (IPCC), and most recently a much-debated report from the Netherlands Environmental Agency about the devastating impact of R134a on climate change over the next decades, had made clear that the danger from HFC direct emissions from MAC must not be understated. The LCCP tool assumes a much lower percentage of HFC-134a leakage in different world regions, taking as a reference new, leak-tighter systems than previously used. As the attached slides show, however, 60% of all R134a produced since 1990 has already been released to the atmosphere, and 80% of all R22 since 1940.
New LCCP tool to account for real-life results
Having so far only incorporated bench tests, the LCCP is now going to accommodate vehicle test results. Over the last years, critics of the model had requested to open the model for fuel over consumption data from real-life testing, collected by carmakers and suppliers. The benefit of avoiding actually driving cycles around the world by replacing them with laboratory simulations had soon turned into the disadvantage of not taking into account experiences gained in the field. The danger that carmakers would use the GREEN-MAC LCCP as an unlimited reference without investing in real-life testing is now meant to be reduced, as in early 2009 working group members agreed to work on a beta version to integrate vehicle A/C results.
Unknown future for GREEN-MAC LCCP
Despite the time already invested in establishing a trustworthy tool and SAE Standard to model the life cycle performance of refrigerants worldwide, further work on the GREEN MAC LCCP model and the integration of real-life testing is now under threat of being significantly delayed, as General Motors struggles with reorganisation under the ongoing bankruptcy process. Still no news have emerged of how the LCCP activity will be conducted in the future and who would lead it.
About the model
The GREEN-MAC-LCCP was developed by General Motors to compare the life cycle climate performance (LCCP) of Mobile Air Conditioning (MAC). It is a comprehensive model integrating a wide set of parameters to calculate the environmental impact of MAC systems and different refrigerants, taking account both direct and indirect emissions over a car’s life cycle. Direct emissions occur during the production of the MAC system and the refrigerant, their transfer to OEMs, refrigerant losses when charging the system and leakage over a car’s lifetime. Refrigerant might also be released in case of a front end accident, and at a car’s end of life, when the system is recycled and the refrigerant is partly recovered. On the other hand, the model calculates indirect emissions (fuel over-consumption) due to increased work of the engine to run the air conditioning.
