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Due to the influence of energy use on electric vehicle range, latent energy storage options could be used to increase thermal comfort and decrease energy consumption during driving. This study focuses on the implications of thermal storage on transient performance of a typical secondary loop system and a combined secondary loop with ice storage system. The use of ice storage in assisting the vapor compression cycle during cabin pull-down and continued cooling, as well as cooling during compressor off periods was experimentally investigated. It was found that the ice storage system was able to decrease energy consumption during pull-down by about 20% and decrease time to comfort by about 15% compared to a regular secondary loop system.

Automotive climate control systems are typically equipped with either an orifice tube or a thermostatic expansion valve. The two devices behave differently especially during cycling operation. The variable restriction of the thermostatic expansion valve delays the refrigerant migration when the clutch is disengaged and allows a faster redistribution when the clutch is engaged. The effect of cycling on the performance of two climate control systems, one with a short-tube orifice, and the other with a thermostatic expansion device, was investigated. The cycle period was varied from 10 seconds to 6 minutes. The test results show the change in moisture removal rate, latent capacity, sensible capacity, energy consumption, and coefficient of performance due to cycling. It is shown that the penalty in energy consumption due to cycling depends on the cycle period.

This paper presents the oil circulation behavior in a CO2 climate control system operating at low evaporating temperature down to -32°C. The increase of oil circulation ratio (OCR) from 0 to 6 wt.% during steady state conditions degrades the coefficient of performance and cooling capacity by 15% and 8%, respectively. The pressure drop across the heat exchangers increases, especially in the gas cooler. In low temperature CO2 systems some fluctuations of oil and refrigerant flow rates were observed during cyclic operations when the system did not equip the oil separator, but was observed only at high oil charge when the system did equip the oil separator. These instabilities lead to a periodic compressor performance fluctuation, which caused system performance degradations. Therefore, the use of an oil separator is recommended for the low temperature operation if an ordinary metering valve is adopted as an expansion device without any special control strategy.