Numerical investigation of a CO2 cooling unit for refrigerating transport operating switching between different configurations

Transport refrigeration systems are usually required to operate in harsh environment and under a highly variable cooling demand. Moreover, as an indirect consequence of the phase out of high GWP synthetic refrigerants imposed by the F-gas Regulation, amongst other options also natural refrigerants are considered for temperature-controlled goods transport applications, optimizing the system design to fit the natural fluids characteristics. This study presents a numerical investigation on the annual energy performance of a new CO2 refrigerating system, developed for a medium-size refrigerated truck, during a typical delivery mission. The system is designed to operate according to three possible configurations, including also the use of a two-phase ejector and an auxiliary evaporator. A dynamic model of the system is developed, considering the possibility to switch between configurations during operation, in order to maximize the COP or the refrigerating capacity, as the performance of the cooling unit is evaluated under different climatic conditions.