Energy-efficient Supermarket CO2 Compressor Pack with Ejectors
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In this thesis, the background of re-implementation of CO2 and the description of refrigeration cycles with R744 compressor and ejector are introduced at first. The following is a case study performed to set up the R744 compressor pack model and library. Relevant pre-simulations were also conducted as an overview study. The simulation work for COP analysis was conducted on a system with an ejector and MT, PAR and LT compressors. It is performed with the necessary data from compressor load operation calculation and efficiency test, which are integrated separately before the simulation work. The operation strategy for the system with 4 parallel compressors applied and the reference system with only 2 compressors applied are specified. The COP of each side and the energy consumption of the two strategies are then compared at last. For load calculation, a simple case study and a real case are analyzed respectively to show how to cover different loads of air conditioning and cooling at medium temperature cabinets with 4 compressors and 2 converters. Also indicated are the load gaps, where the capacity of compressors cannot fully meet the demands. The result provides a design logic and strategy of compressor operation for the simulation work. For the efficiency test, correlations of oil circulation rate, volumetric efficiency, and overall efficiency with different compressor suction and discharge pressure, and revolutions are made from the experiment result for the SINTEF 6-cylinder compressor. The results are compared with the previous tested efficiency value and two commensurate compressor products used in the pre-simulation for the case study. A correlation between efficiency and frequency is also made to modify the overall efficiency of the compressors selected in simulation work. At last the operation strategy of the original compressor pack model and the reference model are specified. The daily cooling load in an hourly time scale is assumed and power consumption of each side for both strategies are presented. The two strategies are then compared in terms of COP on each side, energy consumption on each side and total energy consumption of the two strategy during a typical day. The reference strategy saves around 13.1% of energy compared to the original strategy. Some limitations of the model are shown in the end.