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As a potential replacement to traditional automotive R134a direct expansion (DX) systems, a secondary-loop system allows for the usage of flammable but low-GWP refrigerants such as propane (R290). However, as the secondary-loop system has an additional layer of thermal resistance, the cycle's transient behavior and cabin thermal comfort during pull-down and various driving cycles may be different from traditional DX systems. This paper presents a Modelica-based model to simulate both steady-state and transient operation of automotive secondary-loop systems. The model includes a lumped cabin component and a secondary-loop automotive air-conditioning system component. The air-conditioning system component consists of a condenser, a compressor, an expansion device, a coolant plate type heat exchanger, a coolant to air heat exchanger and a coolant pump. The developed model was validated against both steady-state and transient experimental data for an R290 secondary-loop system.

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.