Zeotrope R32/R125/R134a (10%/70%/20%) is a long-term zero ozone depletion potential (ODP) replacement for low-temperature refrigerant R502. A series of soft optimisation tests has been completed comparing the system performance of this blend with that of R502. The tests were carried out under controlled conditions in a well-instrumented alternative refrigerant test facility using an open-drive reciprocating compressor and counterflow tube-in-tube heat exchangers. Measurements were conducted at two different condensing temperatures - 54.4 deg C (130.0 deg F) and 43.3 deg C (110.0 deg F). The refrigerant evaporating temperature was varied over a range from -30.0 deg C to -15.0 deg C (-22.0 deg F to 5.0 deg F). The refrigerant superheat at the evaporator outlet was maintained at approximately 5.0 deg C (9.0 deg F), and the return gas temperature to the compressor was maintained at 18.3 deg C (65.0 deg F). The degree of liquid subcooling at the condenser outlet was varied between 6.0 deg C and 18.0 deg C (10.8 deg F and 32.4 deg F). 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: optimisation, testing, refrigerants, mixtures, R32, R125, R134a, replacing, comparing, low temperature, performance, reciprocating compressors, counterflow heat exchangers, measuring, fluid flow, liquids, subcooling, coefficient of performance, condensation temperature, calculating, evaporation, temperature, evaporators, properties, capacity