The near azeotropic blend R125/R143a/R134a (44%/52%/4%) is along-term zero-ozone-depletion-potential replacement for the low-temperature refrigerant R502. This blend has recently been assigned refrigerant number R404A by the American Society of Heating, Refrigerating and Air-Conditioning Engineers, Inc. (ASHRAE). A series of tests has been completed comparing the system drop-in performance of this blend with that of R502. The tests were carried out, under controlled conditions in a well-instrumented alternative-refrigerants test facility, using an open-drive reciprocating compressor and counterflow heat exchangers. Measurements were conducted at two different condensing temperatures - 54.4degC (130.0degF) and 43.3degC (110.0degF). The refrigerant-evaporating temperature was varied over a range from -30.0degC to -15.0degC (-22degF to 5.0degF). The refrigerant superheat at the evaporator outlet was maintained at approximately 5.0degC (9.0degF), and the return gas temperature to the compressor was maintained at 18.3degC (65.0degF). The degree of liquid subcooling at the condenser outlet was varied between 6.0degC and 18.0degC (10.8degF and 32.4degF). Test data were used to compare important compressor performance characteristics including shaft power, pressure ratio, and compressor discharge temperature. System performance characteristics were also measured, including evaporator capacity, refrigerant mass flow, and cooling coefficient of performance (COP). The effect of additional liquid subcooling on the evaporator capacity and COP was also evaluated.

KEYWORDS: year 1995, testing, refrigerants, mixtures, comparing, R125, R143a, R134a, R502, azeotropic, R404A, reciprocating compressors, counterflow heat exchangers, measuring, condensation temperature, performance, properties, leaking, coefficient of performance, thermodynamics