Some Safety Studies of a Ternary Refrigerant

A ternary blend of refrigerants composed of HCFC-22, HCFC-142b (chlorodifluoroethane), and a small amount of isobutane, has been used as a drop in substitute for CFC-12 and R-500 refrigerants. It's use as a refrigerant was presented at the Purdue 1992 International Refrigeration Conference--Energy Efficiency and New Refrigerants[ I] . This paper will cover safety related issues and testing performed to date. Results of fractionation and flammability testing will be presented. Comparisons of flammability, energy of combustion, and rate of combustion with ammonia, and hydrocarbons will also be shown. INTRODUCTION There are several problems to developing a "drop"in" substitute for CFC-12 for use ·in existing equipment. The substitute must have suitable thermodynamic properties, be nonexplosive and nonflammable or very weakly flammable at best, must be miscible with mineral oil. must be compatible with system materiels, must be low toxicity or be an "old" substance which has established toxicity, and finally it must be affordable. While acceptable for new equipment manufacture, HFC-134a is not a simple drop-in for CFC-12 in existing applications. HCFC-134a is not miscible in mineral oils used in CFC-12 systems. Nonmisicibility may cause oil to become entrapped "logged" in the evaporator, causing low performance and compressor failure due to oil starvation. Newly developed lubricants, such as polyalkylene glycol (PAG) based (for automotive use) and polyol ester based (for most everything else) lubricants, are useable in newly manufactured equipment, which is usually built in clean, uncontaminated environments. However, for equipment which has to be serviced in the field, such as CFC-12 equipment which has been retrofitted to HFC-134a and one of the above oils, there are still be problems to be overcome. PAG oils are very sensitive to moisture contamination, and will break down in the presence of chlorides (from CFC-12 previously being run in the system). It is usually impossible to "flush" the chlorides since they are tightly embedded on the inside surface of parts. Aluminum, in particular, will have the inside surfaces partly converted to aluminum chloride. Ester based oils are more tolerant of residual chlorides, but are very sensitive to moisture contamination. Ester oils may break down into fatty acids and alcohols from contamination. Also, both PAG and Ester oils may sometimes have problems maintaining enough lubricity in CFC-12 equipment. Much research is underway worldwide to solve or reduce these problems. In addition, materiels used in components of some older compressors are incompatible with many synthetic oils. Both PAG and ester oils may also have thermal stability problems[2], although it is possible that the use of various additives may mitigate this problem. There currently exist suitable blends which may be "near" drop-in substituted for CFC-12 in some applications, pro-