Capacity control method of a CO2 ejector-based refrigeration system using a thermoelectric-aided subcooler

An ejector technology is among the most promising solutions in vapour compression units, especially for CO₂ systems, to reduce the industry’s environmental impact and energy consumption. Nevertheless, the design of two-phase ejectors requires a complex capacity control that may limit the applicability for small-scale units. Therefore, the main objective of this paper is to experimentally evaluate a fast and robust control method of a single two-phase ejector by implementing a thermoelectric-aided subcooler (TESC) in a CO₂ ejector-based refrigeration supermarket system. The TESC implementation can adjust the ejector motive nozzle, thereby influencing the motive mass flow rate and overall ejector efficiency. The testing was conducted using TESC mounted upstream of the ejector motive nozzle for typical medium-temperature evaporation at different gas cooler outlet temperatures ranging from 30.0 °C to 39.0 °C to meet hot and tropical climate zones. Based on experimental results, the TESC implementation allowed for the increase of the ejector motive mass flow rate over 10% when the TESC voltage was controlled within 10.0 V. Finally, the simple simulation of the TESC CO₂ ejector-based cycle confirmed the potential for a COP improvement over 5.0% and a cooling capacity increase of up to 21.2% compared with those of the standard ejector-based system.