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HFC refrigerants The global warming potential is extremely low (GWP = 4). When released to the atmos- phere, the molecule rapidly disintegrates within a few days, resulting in a very low GWP. This raises certain concerns regard- ing the long-term stability in refrigeration cir- cuits under real conditions. However, extensive testing has demonstrat- ed the required stability for mobile air condi- tioning systems. R1234yf has lower flammability as meas- ured by ASTM 681, but requires signifi- cantly more ignition energy than R152a, for instance. Due to its low burning velocity and the high ignition force, it received a classifi- cation of the new safety group "A2L" ac- cording to ISO 817. In extensive test series, it has been shown that a potentially increased risk of the refrig- erant flammability in MAC systems can be avoided by implementing suitable construc- tive measures. However, some investiga- tions (e.g. by Daimler) also show an in- creased risk. This is why various manu- facturers have intensified again the devel- opment of alternative technologies. Toxicity investigations have shown very positive results, as well as compatibility tests of the plastic and elastomer materials used in the refrigeration circuit. Some lubri- cants show increased chemical reactivity which, however, can be suppressed by a suitable formulation and/or addition of "stabilizers". Operating experiences gained from labora- tory and field trials to date allow a positive assessment, particularly with regard to per- formance and efficiency behaviour. For the usual range of mobile air conditioning oper- ation, refrigerating capacity and coefficient of performance (COP) are within a range of 5% compared with that of R134a. There- fore, it is expected that simple system mod- ifications will provide the same performance and efficiency as with R134a. The critical temperature and pressure lev- els are also similar, while the vapour densi- ties and mass flows are approximately 20% higher. The discharge gas temperature with this application is up to 10 K lower. With a view to the relatively simple conver- sion of mobile air conditioning systems, this technology prevailed up to now over the competing CO2 systems. However, as already explained before, due to the flammability of R1234yf, investiga- tions focus on other technical solutions. This includes active fire-extinguishing de- vices (e.g. with argon), but also enhance- ments of CO2 systems. For detailed information on properties and the application, see chapter "Low GWP" HFOs and HFO/HFC blends as alternatives to HFCs, page 24. 12PDF Image | REFRIGERANT REPORT 21
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