Theoretical analysis of CO2 trans-critical system with parallel compression for heat recovery and air conditioning in supermarkets

This paper theoretically analyses a CO2 trans-critical booster system in which parallel compression, heat recovery and air conditioning are integrated. The performance of the system is studied in various running modes using flash gas by-pass (FGBP) or parallel compression (PC). These running modes include summer cases with/without air conditioning and winter case with heat recovery. The results show that parallel compression is more efficient than flash gas by-pass in summer cases; the increase in COPtot is up to 14% comparing the best cases for PC and FGBP. The increase in COPtot in winter heat recovery mode is marginal, less than 4-6% and hardly-feasible in practice. Comparing the AC function of the CO2 system with a conventional HFC air conditioning system, it has been found that CO2 system is more efficient in moderate ambient temperatures lower than 20-25°C. The CO2 system's AC performance is less efficient than HFC solution in ambient temperatures higher than 25°C. To conclude, an integrated CO2 trans-critical booster system can to provide the entire supermarket's refrigeration and air conditioning demands for cold-mild climates with comparable or higher energy efficiency than the HFC solutions.