Experimental and computer performance study of an automotive air conditioning system with alternative refrigerants

Abstract

A computational model with the objective of simulating the performance of an ideal automotive air conditioning system, working with several refrigerants, is presented. The main function of this model was to determine the most suitable alternative refrigerant for R-12. Some assumptions about the losses and irreversibilities were embodied in this model for more realistic results. The effects of several parameters on system performance and compatibility were investigated, including evaporating temperature, condensing temperature and compressor rotational speed. Five refrigerants were studied by this model, including R-12, R-134a, R-290, R-600a and a mixture of propane and isobutane R290/R600a (62/38, molar percentage). The model predicted that the mixture (R290/R600a) was the most suitable alternative for R-12 and that several modifications should be performed when the other alternative refrigerants are used in the R-12 system. The major part of this work was an experimental investigation for the use of R290/R600a as a drop-in alternative for R-12 in a prototype automotive air conditioning system. Ninety-two (92) tests were conducted on both refrigerants to study the effect of four parameters on system performance. These were outdoor air temperature, cooling load, compressor rotational speed and the soaking temperature. Three outdoor air temperatures were considered, 35, 40 and 50 °C. Six rotational speeds were employed, 700, 1000, 1500, 2000, 2500 and 3000 rpm, whereas four cooling loads were simulated in the evaporator chamber, 1000, 2000, 3000 and 3500 W. The evaporator chamber was soaked at five temperatures, 45, 50, 55, 60 and 65 °C. Two types of tests were performed, including single operation mode tests and multi-operation modes tests. There was close similarity between the performance of the R290/R600a mixture and R-12 with superiority for R-12 in the working pressures, energy consumption and the COP values, whereas the mixture (R290/R600a) outperformed R-12 in the subcooling, superheating, evaporator discharge air temperature and the cooldown time. The results of this work showed good agreement with the experimental and theoretical results available in the literature.