Data-driven energy efficiency comparison between operating R744 and R448A supermarket refrigeration systems based on hybrid experimental-simulation analysis

A comprehensive study is presented concerning the energy performance comparison between two distinct operating supermarket refrigeration arrangements located in separate stores in Athens, Greece. The first supermarket under investigation is supported by a transcritical R744 booster unit featuring parallel compression, liquid ejectors and internal heat exchangers, while the second supermarket is supported by one mediumtemperature and one low-temperature R448A direct expansion arrangement. Detailed measurements of pressure, temperature and energy consumption of the compressor racks were collected and analyzed for the refrigeration setups of both supermarkets. By employing the obtained measurements, a calculation model is developed and verified for the R448A systems, which uses as inputs the ambient temperature and the refrigeration loads of the store and provides as output the corresponding compressors' energy consumption. The calculated refrigeration loads of the R744 store are used as inputs in the developed R448A model, and the extracted energy consumption results are compared to the measured energy figures of the R744 unit. The parametric analysis revealed that for the compared systems and their respective settings, the R448A units outperform the R744 arrangement approximately above the ambient temperature of 24 degrees C. Regarding the performance of the systems for operation under the conditions of the same supermarket, the analysis proved that the R744 unit consumes 0.90 % less annual energy compared to the R448A systems, displaying 21.35 % less energy consumption during January, but also 16.99 % more energy consumption during July.