Low-GWP Refrigerants and Flammability Classification

摘要

Research on new refrigerants over the past 15 years has led to selection of either "old" refrigerants such as hydrocarbons, ammonia, and CO2, or recently unsaturated HFCs such as R-1234yf. Toxicity issues forbid the use of potentially toxic refrigerants as demonstrated by the failure of both DP1 and AC1 refrigerant blends. Flammability is a different matter because leanly flammable substances can be used if properly handled. Since 1995, research has been carried out in Japan, Europe, and the USA for flammability classification of refrigerants. The burning velocity (BV) and the minimum ignition energy (MIE) are fundamental physical properties allowing the classification of refrigerants according to their flammability. This classification is of importance as it makes it possible to mitigate flammability risks in a rational manner. ISO 817 has elaborated a new threshold in order to differentiate between moderately flammable substances. In fact, the burning velocity and the MIE allow precise ranking of risks related to the use of flammable substances. Several methods have been proposed for the calculation of flammability of refrigerant blends such as the RF numbers. The future of low-GWP refrigerants is definitively related to risk mitigation of either toxicity (for ammonia only) or flammability. A new international classification is necessary in order to take appropriate measures to use safely low-GWP refrigerants according to the refrigerant charge and the refrigeration capacity.