Experimental performance of a mobile air conditioning unit with small thermal energy storage for idle stop/start vehicles.

In this study, an attempt was made to extend the comfort of a passenger car cabin during the compressor off cycle using thermal energy storage (TES) in an HFO-1234yf mobile air conditioning (MAC) unit for idle stop/start vehicles. Fatty acid (OM08), as a phase change material (PCM), with 0.1–0.5 vol% of graphene nanoplatelets (GnPs) was used in this study. It was found that the inclusion of GnPs increases the thermal conductivity and dynamic viscosity of the liquid PCM nanocomposites by ~ 46% and ~ 53%, respectively, with 0.5 vol% of GnPs. During the pull-down cycle, the enhanced thermal conductivity outweighs the increased dynamic viscosity, resulting in a quicker decrease in PCM temperature. The test results revealed that the cabin temperature increases through the addition of TES, with a marginal decrease in the coefficient of performance. The addition of TES with the use of pure PCM increases the compressor power consumption of the MAC system by less than 1%. However, with the inclusion of graphene the power consumption increases with respect to the volume fraction. Without TES, the cabin comfort is extended by 78 s, 60 s, and 43 s for heating loads of 500, 1000, and 1500 W, respectively, and with the inclusion of TES, using pure PCM, the cabin comfort increased by up to 106 s, 87 s, and 63 s, respectively. The inclusion of 0.5 vol% GnPs extends the cabin comfort further by up to 189 s, 147 s, and 105 s for heating loads of 500, 1000, and 1500 W, respectively. Further, the CO2 equivalent emissions of the MAC system with TES using a pure PCM and a PCM nanocomposite are 10.54% and 5.64% lower than that of the system without TES, respectively. [ABSTRACT FROM AUTHOR]