Variable capacity control strategy for an automobile air conditioning system

Abstract

Conventional vehicle air conditioning system often uses an engine-driven compressor where it operates according to engine speed. This causes cooling capacity fluctuation that leads to low passenger thermal comfort. Furthermore, designers usually oversize the air conditioning system to speed up the cooling time, regardless of the ambient condition and vehicle speed, which leads to high energy and fuel consumption of the vehicle. Thus, this research investigates the feasibility of independent electric direct current (DC) compressor retrofit into conventional petrol vehicle air conditioning system and while developing an intelligent fuzzy logic controller (FLC) for better control of the vehicle compartment temperature and lower the fuel consumption. This study was implemented on a compact passenger vehicle with original engine-driven compressor air conditioning system. First, the average cabin temperature, air conditioning performance and fuel consumption of the vehicle with original engine-driven compressor was obtained. Second, the DC compressor was retrofitted and the original on/off controller was used. The steady-state vehicle compartment temperature was also measured at various DC compressor speed to support the development of the FLC for variable speed control (VSC). Next, the VSC was implemented and all the data were compared. The experiments were carried out on a chassis dynamometer (or called rolling road) with variable internal heat load and temperature setting. The results indicate that the variable capacity control strategy on the DC compressor with the FLC control system give positive results, with lower fuel consumption, higher coefficient of performance (COP) and enhanced temperature control compared to engine driven compressor with on/off controller and DC compressor with on/off controller. The implementation of the intelligent DC compressor system gives higher energy efficiency to vehicles while providing better temperature control, thus enhancing the driving experience.