Annual performance of a supermarket refrigeration system using different configurations with CO2 refrigerant

The recent regulation concerning the ban of the hydro-fluorocarbon (HFC) refrigerants has led to the employment of environmentally friendly solutions for refrigeration. Systems that employ CO2 seem to be a viable option which is compatible with the current legislation. The objective of the present work is the investigation of ten different refrigeration systems with CO2 and to compare them with a conventional system with R404A in energetic terms. The analysis is conducted on an annual basis by using the measured energy consumptions and loads for an existing system with R404A. Except for the refrigeration system comparison, a model for the prediction of the hourly refrigeration loads of the existing supermarket is developed using experimental results. This model is applied for the yearly evaluation of the proposed CO2 refrigeration systems. The examined CO2 system configurations include a simple booster system, a system with parallel compression, a system with parallel compression and overfed evaporators in the medium temperature, a system with parallel compression and overfed evaporators in both medium and low temperature, a system similar to the last one with the addition of an intercooler after the low temperature compressors, and all the aforementioned systems with the addition of a mechanical subcooling cycle after the gas cooler. According to the final results, the most promising configuration is the one with parallel compression, overfed evaporators in medium and low temperature, intercooler and mechanical subcooling, which leads to 8.53% yearly electricity savings compared to the conventional R404A system. Moreover, it is important to state that the simple booster CO2 system is found to be less efficient than the conventional R404A system with 15.23% higher yearly electricity consumption.