Performance assessment of a two-stage CO2 small scale MT refrigerator

• Published in: International journal of refrigeration Vol. 131; pp. 887 - 896
• Main Authors: Citarella, Biagio, Mastrullo, Rita, Mauro, Alfonso W., Sfragara, Massimiliano, Tammaro, Marcello
• Format: Journal Article
• Language: English
• Published: Paris Elsevier B.V 01.11.2021; Elsevier Science Ltd
• Subjects: Bi-étagé; Carbon dioxide; CO2; Compressors; Condensing unit; Coolers; Flammability; Froid [artificiel]; High temperature; Hydrofluorocarbons; Intercooler; Inverter; Leakage; Performance assessment; Performance indices; Refrigerants; Refrigeration; Refrigerators; Refroidisseur intermédiaire; Rolling piston compressors; Two stage; Unité de condensation; Variateur de fréquence; Inverter; Refroidisseur intermédiaire; Two stage; Unité de condensation; Variateur de fréquence; CO2; Intercooler; Froid [artificiel]; Refrigeration; Bi-étagé; Condensing unit
• ISSN: 0140-7007; 1879-2081
• DOI: 10.1016/j.ijrefrig.2020.12.024

•Experimental campaign on a two-stage condensing unit using CO2 as refrigerant.•Hermetic rotary two-stage compressor with inverter, intercooler, flash gas removal.•Cooling capacity and COP decrease with ambient temperature and without intercooler.•Flash gas removal cooling effect increase with ambient temperature.•The unit fulfils the SEPR requirement as prescribed in EU 2015/1095. F-GAS regulation has introduced important limitations in the use of refrigerants in the small size commercial refrigeration sector, with a maximum GWP=150 since 2022, forbidding the use of R404A. Among alternatives, there are propane, low-GWP HFC/HFO mixtures or pure HFOs: each of them can be considered as an option depending on the refrigerant charge limit for the application or by the total cost accepted by customer. In case of remotely connected units with potential refrigerant leakages, such as condensing units, the use of CO2 is considered as an option, due to the its safety indexes (no toxic and no flammable) which enables the use of larger amount of refrigerant. Being the CO2 refrigerant cycle trans-critical in warm climates, it may have low COPs and not fulfil the limits imposed by Ecodesign rules. In this paper, a condensing unit working with R744 is experimentally tested to assess the performance according to EN13215:2016. To limit high temperature at the compressor outlet, a two-stage system working with an inverter-driven hermetic rolling piston compressor is considered with intercooler and flash gas removal at intermediate pressure. It has been verified that seasonal energy performance ratio (SEPR) can be over the threshold value of 2.3 applied since 2018.