Commercial refrigeration systems represent some of the largest energy consumers in supermarkets, and therefore particular attention needs to be paid to increasing energy efficiency to reduce overall energy consumption and meet climate goals by 2030. This study investigates the performance of a CO₂ (R744) commercial refrigeration system with evaporators operating alternately in dry and flooded modes. This operation is possible due to a particular adjustment using liquid sensors installed in the middle of both low-temperature (LT) and medium-temperature (MT) liquid separators, which transmit information to the controllers that regulate the compressor rack and evaporators, to switch from dry to flooded operation when the liquid level rises and vice versa when the level drops. The results show that the correct regulation of the system of 50% with 6K superheat operation and 50% with 3K superheat operation on MT evaporators, respectively, and 50% with 6K superheat operation and 50% with 4K superheat operation on LT evaporators leads to a reduction of energy consumption compared to 100% operation of all evaporators with 6K superheat by 6.9% per year for the compressor rack.

Integrating ejectors into CO₂ transcritical refrigeration systems to reduce energy consumption has been performed successfully throughout the industry in recent years. The objective of the present work is to investigate the effect of indoor and outdoor operating conditions on the energy efficiency of ejector expansion supermarket refrigeration plants. The analysis uses the measured energy consumptions and loads for two supermarket refrigeration plants operating in two cities in the Republic of Moldova (Chisinau and Balti). A model for the prediction of the plant’s annual energy consumption and the loads of the refrigeration and freezing compressors is developed using experimental results. Although there are theoretical and experimental analyses of the investigated systems in the specialized literature, no studies were found in the specialized literature regarding energy consumption increase due to pressure losses through the pipe route in transcritical CO₂ refrigeration installations with an ejector for supermarkets. The results indicate that refrigeration compressors have a greater increase in energy consumption than freezing compressors with increases in the outdoor temperature. The study shows that the additional drop in evaporating pressure at the compressor rack due to incorrect sizing of the pipe route leads to higher energy consumption compared to what the same plant would consume if the pipe route were correctly sized and executed. For every one-degree increase in temperature loss due to additional pressure drop through the pipeline, the entire plant consumes around 1.5% more energy. Knowledge of these performance data of real systems provides designers and manufacturers with clues to understand the importance of the correct design of the pipe route to obtain maximum energy efficiency.

Carbon dioxide is the number one choice for use as a natural refrigerant for environmentally friendly and sustainable solutions in refrigeration technologies today. It is used for new installations required for all types of applications, from small cold rooms in restaurants or supermarkets to large industrial applications. Practically, it is used to cool down solid products or liquids. Due to its significant inefficiencies, especially related to high operating pressures and throttling processes, the basic CO₂ transcritical refrigeration system requires improvement for superior overall efficiency. For this reason, this review paper provides insight into four types of improved CO₂ transcritical refrigeration systems: first, a CO₂ transcritical refrigeration system with one EJ or dual EJs, parallel compression, and mechanical subcooling; second, a CO₂ transcritical refrigeration system with two-stage heat recovery and a GS/CC heat exchanger; third, a CO₂ transcritical refrigeration system with two-stage compression and intermediary gas supplementation; and fourth, a solar-assisted ejector subcooling CO₂ transcritical refrigeration system. These systems provide COP increases of 21.6%, 26.3%, 25%, up to 30.1%, and 3.4%, as calculated for certain conditions. This review paper explains the mathematical modulation assumptions, energy model construction, heat recovery thermodynamic principle, and conventional and advanced exergy evaluation. As a result, all four improved CO₂ transcritical systems have superior efficiency when compared with standard CO₂ transcritical systems, consuming less energy and being suitable for use in real applications.

The EJ installation as a method to reduce energy consumption in commercial refrigeration plants with CO2 refrigerant has been successfully used by the whole industry in recent years. However, the heat transfer surface of the EV, both on LT and MT consumers, could not be utilized at the maximum capacity because it could not operate at all the time flooded, due to the possibility of liquid droplets entering the compressor’s crankcase. No studies have been found so far in the specialized literature on improving the energy consumption of transcritical CO2 refrigeration systems in supermarkets that use an EJ on the suction line of the medium-temperature liquid separator. In this paper, the authors analysed a new booster transcritical refrigeration system with EJ and droplet separators, on both cooling circuits, installed in southern Romania, and compare it with standard CO2 booster refrigeration system. Taking advantage of the experimental measurements, the mathematical model is validated and allows the prediction of the annual performance of the installation under field operating conditions. The model considers how indoor and outdoor conditions impact energy efficiency. The results showed a significant reduction of energy consumption by 18.3% at the compressor rack level, and by 6.3% at the entire plant, compared to the standard CO2 transcritical booster system. The new system was also analysed regarding the overall exergy efficiency, and the results indicated an improved efficiency between 7 and 10%, depending on the exterior temperature variance. Knowledge of these performance data from actual installation, equipped with EJ on the medium temperature suction line liquid separator gives the entire industry the opportunity to promote this type of plant for future installations.