**8. HFC 134A: Present day refrigerant**

HFC-134a (Tetra fluro ethane) presently is the leading candidate to replace CFC-12. The main culprit chlorine atom is absent in the molecule of HFC-134a, hence this substance provides excellent chemical and thermal stability, significantly better than CFC-12.It has got zero Ozone Depleting Potential (ODP) and Global Warming Potential (GWP) of 0.115. All toxicological studies on HFC-134a have been completed including one-year inhalation study with favorable results. Wilson et al. conducted a detail study and reported the thermodynamic properties of HFC-134a. The thermodynamic properties of HFC-134a are very much similar to CFC-12. Normal boiling point (NBP) of HFC-134 a is – 26.8 deg. C which is very near to normal boiling point of CFC-12 (29 .8 deg. C). McLinden considered the use of HFC-134a to be the most realistic refrigerant to CFC-12. Thermal conductivity and viscosity were measured over a temperature range temperatures and reported by Shank land et al. Lot of research works were carried out on different aspects of using HFC134a as a real substitute to CFC12. The use of oil in HFC 134 a systems requires a very stringent quality control. Some researchers reported that HFC-134a has been proved as a fully reliable refrigerant in retrofitting CFC-12 systems including centrifugal chillers, semi-hermetic reciprocating and screw compressors and HFC-134a is not the most suitable option for the hermetic systems.

Boot in his paper "Overview of Alternatives to CFCs for Domestic Refrigerators and Freezers" concluded that alternatives beyond HFC-134a must be considered

owing to the inefficiency of HFC-134a when used in a refrigerator. Vineyard et al. performed tests with HFC-134a in a standard household refrigerator and concluded that HFC-134a consumes more energy than that of CFC-12. From the thermodynamic data, it can be estimated that HFC-134a has a lower capacity and operates at lower suction and higher discharge pressure than CFC-12 for the same evaporating and condensing temperatures. Based on this information, a larger compressor would be necessary to achieve capacities equivalent to those obtained with CFC-12.
