Conference Year

2014

Keywords

Automotive, Refrigerant Charge, Compressor speed, Air flow, COP.

Abstract

During last few decades research on Automotive Air Conditioning System (AACS) reached a milestone in terms of comfort, safety and economy. However investigation on system performance due to AACS’s variable operating conditions is limited. The performance of any AACS mostly depends on compressor speed, blower speed, refrigerant charge level and ambient condition. However, the combined effect of these parameters on the performance of AACS could be non-intuitive. Reduction in compressor speed and blower speed reduces the cooling capacity. Again, higher blower speed induces large volume of fresh air inside the cabin, which requires more compression work to maintain the same comfort level. Further the best performance of the system is achieved at an optimum charge level which is not independent of the other operating conditions. Therefore, it is essential to assess the performance of AACS for a wide combination of operating variables so that the range of optimum operating zone can be identified. With this purpose, an off board test bench has been developed for evaluating the performance of an automotive air conditioning system. The facility consists of the mechanical hardware used in an automobile along with a large number of additional sensors and a standalone control system that mimics the operations in a car. The experiments were carried out with varying compressor and blower speed along with a variable refrigerant charge for a given ambient condition. Total sixty set of experiments were conducted at 200, 300, 400, 500 and 600 g of refrigerant charge level. In each charge level the speed of the compressor was fixed at 1000, 1300, 1600 and 1900 rpm by using a variable frequency drive. Again in each compressor speed, the blower speed of the evaporator was selected at three different set points. The cooling capacity, compression work and COP of the system are reported in this paper over this wide operating range. It is observed that with the increase in compressor speed, cooling capacity and compression work increases along with a decrease in the COP of the system. The results indicate that the AACS could operate over a wide range of charge levels, 15% below to 15% above the design value without any significant impact on its performance. Beyond this range, the performance of the system was found to be strongly dependent upon the charge level. The degree of superheat at the evaporator outlet and degree of subcooling at the condenser outlet were shown to be significantly dependent on the level of refrigerant charge. Though the system performance depends on the speed of both the compressor and the blower, the effect of the latter on the refrigeration cycle is only marginal. The optimum operating condition with compressor and blower speed along with refrigerant charge level has also been identified.

2399_presentation.pdf (7922 kB)
Effect of Refrigerant Charge, Compressor Speed and Air Flow through the Evaporator on the Performance of an Automative Air Conditioning System

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