Performance Enhancement Research of a CO₂ Air Conditioning System with Propane Mechanical Subcooling for Electric Vehicle

Abstract

The driving range of electric vehicle can be significantly reduced if using CO₂ as a refrigerant in hot climates. This paper aims to improve the performance of CO₂ electric vehicle air conditioning system by using a dedicated propane mechanical subcooling, the interference between internal heat exchanger (IHX) and mechanical subcooling (MS) was discussed, since both improvements compete towards reducing the throttling losses, optimization possibilities were theoretically analyzed on several integrated system for various subcooling degrees from 3℃ to 15℃ and ambient temperatures from 25℃ to 40℃, results show that the presence of mechanical subcooling after IHX reduces its efficiency, the use of mechanical subcooling simultaneously before IHX rather yields a more efficient air conditioning system. It has been shown that compared with CO₂ prototype system, the new best integrated system can improve the COP (coefficient of performance) up to a maximum of 25.72% despite the extra compression work in mechanical subcooling cycle, and the cooling capacity up to a maximum of 46.24% during the research range, thus, the driving range of EVs can be significantly extended. Furthermore, the suitable cooling capacity and propane compressor displacement required in the MS cycle are predicted. Finally, experiments were carried out to see the actual improvements achieved by MS and IHX cycle based on the theoretical results.