Experimental performance evaluation for a carbon dioxide light commercial cooling application under transcritical and subcritical conditions

CO2 is one of the most interesting non toxic, nor flammable, low GWP natural fluid to be used in applications with a large direct contribution to global warming, such as vending machines. In this paper the results of an experimental investigation on a small capacity, air-forced refrigerating plant working with CO2 are presented. The air inlet temperatures at gas cooler and evaporator were varied between 16 °C and 31 °C and between −25 °C and 25 °C, respectively, to cover the range of temperatures under conditions typical of commercial refrigeration, during quasi-steady operation. The thermodynamic analysis of the system performance was carried on varying independently the pressure at the gas cooler, by overfeeding the liquid receiver to point out the effect of refrigerant charge. The results allow to describe the performance of the system in a map varying the boundary conditions; at the same time the corresponding variations of the thermodynamic cycle, the COP and the mass flow rate are reported. ► A light commercial refrigerating plant working with CO2 was tested in order to evaluate its performance. ► 71 experimental points were collected varying the flow rates, the temperatures of air sources and the refrigerant charge. ► Mass flow rate, cooling capacity, electrical power and COP were evaluated as a function of pressures and superheating. ► The segregate influence of each operating parameter on each performance indicator was calculated. ► A map of plant performance as a function of air source temperatures is reported.