Drop-In Substitutes for R502: The Role of HCFC22 and HC290

R502 is due to be banned in the near future, and ti)e need for an immediately available and easy-to-use alternative is becoming more and more urgent. Retrofitting refrigerating units can prove easier and less expensive if the mineral or alkylbenzene lubricants usually adopted with R502 have a certain miscibility in the drop-in mixtures. This paper examines the near-azeotropic mixture Rl43a/290/22 evaluating the influence of the R22 and of R290 mass fractions on the oil miscibility and on operating conditions in the refrigerating units. INTRODUCTION R502 is currently the most commonly used refrigerant in commercial cold storage; it is due to be banned worldwide by January 1st, 1996, according to the Copenhagen amendment of the Montreal Protocol, and by January I st, 1995 within the European Union according to a 1992 EEC Regulation. Suitable alternatives for retrofitting refrigerating units should therefore become available very soon. Individual halogenated hydrocarbons have been investigated with poor results and more efforts are now being dedicated to binary or ternary mixtures. The mixtures selected for replacing R502 can be divided into two categories: the zero Ozone Depletion Potential (ODP) mixtures, designed for original equipment manufacturers (OEMs); mixtures containing HCFC (mostly R22), which are inunediately available and intended for retrofitting refrigerating units in the short term. A few zero ODP mixtures have been developed and are now available. Their use as drop-in refrigerants raises some concern because polyol-ester lubricants are frequently required. The mineral or alkylbenzene oils usually adopted with R502 have to be replaced, and several charges of the refrigerant and lubricant are needed to achieve a satisfactory procedure. On the other hand, mixtures based on HCFCs can prove effective alternatives for retrofitting R502 units: a certain compatibility with mineral and alkylbenzene lubricants is their most important feature; their components are all well known and they also offer immediate availability and good performance. The development of short-term mixtures containing HCFCs was suggested after the signing of the Montreal Protocol because no suitable substitute for R502 was known at the time. The Copenhagen amendment of the Montreal Protocol calls for the phase-out of HCFCs with a time schedule that allows for their use in drop-in mixtures !eplacing R502 in existing plants (up until January 1st, 2030). In December 1992, the European Communities Union defined a new phase-out schedule for HCFCs, setting the fmal ban at January )st, 2015. In Germany and Italy the phase-out has been brought forward to January Jst, 2000. Nonetheless, R22 and all the other HCFCs have to be taken into consideration for the formulation of short-term substitutes of R502 in order to make retrofitting easier and less expensive. Some R22-based mixtures are already available, and many have responded well to tests in refrigerating equipment without making any changes to the circuit or lubricating oil. The Institute for Refrigeration of the Italian National Research Council is involved in investigating refrigerant mixtures, and the Ausimont company intends to present a drop-in substitute for