Discharge Gas Temperature Control in Reciprocating Hermetic Compressors Modified for R134a/R22 Refrigerants Operation as Substitutes of Present R12/R502

Discharge gas temperature value is an indicator of compressor safe operating conditions, particularly on R12 and R502 commercial applications. These refrigerants will be replaced very soon by R134a and R22 respectively, also if R22 is not considered a final solution. High discharge temperatures are typical in LBP-R22 hermetic compressors operating at low evaporating temperature as low as -40"C; lower values are found in LBP-R12 compressors operating at R134a, but with limitations to about -30°C evaporating temperature to avoid volumetflc efficiency losses. Modifications were mtroduced on LBP R502 compressors to reduce the discharge temperature on R22 operations; the final solution was to shift the discharge muffler from crankcase to cylinder head, limiting the heat transfer to cylmder. The same prmciple, tested on LBP R12/R134a compressors, confirmed lower discharge temperatures bur with margmal effects on performances. Introduction The present work is mainly related to hermetic recipro.compressors series tor l9P commercial applications, ranging up to 1050 W max rated capacity at R502. Max displacement 20.4 cm3. These compressors must work safely at evaporating temperatures as low as -40"C and withstand the high discharge pressure during pull-down periods. Care must be taken to avoid excessive superheating of return gas; a suction temperature of 1 B"C is recommended. The commonly used refrigerant for these applications is R502. Refrigerant R12 is also used but with evaporating temperature limitation at value of -30°C. For both refrigerants it was necessary to find a shon-term substitution to accomplish the growing trend to ban CFC first from public-addressed-appliances, like s"per-market distribution of frozen foods. The results obtained to improve R502 operation are poSitively applicable also to R12 refrigerant compressors. The choice was to use A22 as replacement of R502 for these reasons . low Ozone-Depletoon-Potentiai (0.05 vs.0.3 of R502 and 1.0 of R12) easy supply and low cost available l"bricants (naphtenic or synthetic oils) not yet available R22 replacement The R134a substitution o1 R502 was not considered for these reasons :