Abstract
In the last century, the refrigerant R744 (carbon dioxide) has become an environmentally friendly solution in commercial refrigeration despite its particular issues related to the low critical temperature. The use of transcritical cycles in warm and hot countries reveals the necessity of adopting different configurations and technologies to improve this specific cycle. Among these, subcooling methods are well-known techniques to enhance the cooling capacity and the Coefficient of Performance (COP) of the cycle. In this work, an R600a dedicated mechanical subcooling system has been experimentally tested in an R744 transcritical system at different operating conditions. The results have been compared with those obtained using a suction-to-liquid heat exchanger (IHX) to determine the degree of improvement of the mechanical subcooling system. Using the experimental tests, a computational model has been developed and validated to predict the optimal subcooling degree and the cubic capacity of the mechanical subcooling compressor. Finally, the model has been used to analyze the effect of using different refrigerants in the mechanical subcooling unit finding that the hydrocarbon R290 and the HFC R152a are the most suitable fluids.
Highlights
Carbon dioxide (CO2 ) has been established as a sustainable working fluid in commercial refrigeration encouraged for its environmental friendless, high-security classification and excellent properties and because it is a natural substance with an extensive background in the industry
The results demonstrated that all the subcooling systems were able to reduce the heat-rejection pressure and gave energy savings between 25% and 36% using the system without subcooling as a reference
Refrigerants R152a and R290 need need higher subcooling degrees to reach the optimal performance in contrast with
Summary
Carbon dioxide (CO2 ) has been established as a sustainable working fluid in commercial refrigeration encouraged for its environmental friendless, high-security classification and excellent properties and because it is a natural substance with an extensive background in the industry. The results at a fixed evaporating temperature of −10 ◦ C and heat-rejection conditions of 35 ◦ C, showed improvements of up to 40.9% in terms of cooling capacity and up to 17.3% in the optimal COP, taking a single-stage transcritical cycle without IHX as a reference. The results obtained for the evaporative levels of −7 and −28 ◦ C and several temperatures for the heat rejection, demonstrated a substantial COP improvement from 10 to 15% depending on the load ratio compared with the refrigeration system without subcooling. The experimental results have been analyzed and discussed, obtaining the key parameters used to maximize the COP of the plant by optimizing the mechanical subcooling system using the to develop a computational model validated with the experimental tests This model has been low-GWP in COP accordance withbythe. Has been performed at −10 °C typically used in commercial refrigeration
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