To investigate the temperature distribution and optimize the thermal performance of a vehicle carriage for transporting refrigerated vaccines

a 3.9 m3 vehicle carriage working within the temperature range of 2–8 °C is examined in this study. Four factors

namely

solar radiation intensity

air duct structure

refrigeration unit switch

and door curtain

which influence the thermal performance

are experimentally studied at a compressor speed of 1 800 r/min. The uniformity of the temperature distribution and the temperature change rate during the measurement period are comprehensively analyzed. The results show that when the vaccine refrigeration vehicle is maintained under an average solar radiation intensity of 295.94 W/m2and 82.78 W/m2 for two hours

the average temperature in the carriage under the former condition is 1.326 °C higher than that under the latter. The on-off frequencies of the refrigeration units increase

and the energy consumption of the vehicle increases. The application of the air duct structure can help reduce the local hot spots in the carriage

and the rate of pre-cooling increases by 0.006 °C/s. Moreover

when the carriage door is opened for 120 s

continuous operation of the refrigeration unit enhances the airflow heat exchange between the inside and outside of the carriage

which noticeably disturbs the temperature distribution in the vehicle. Therefore

closing the refrigerating unit is recommended when the vehicle door is opened. The curtain can effectively prevent cold air from exchanging heat with the environment and maintain the low temperature of the carriage.