Investigations On Energy Performance Of Two Stages R744 Central Refrigeration System For Supermarkets

As global warming and ozone depletion are becoming increasingly serious,it is of great importance to cut the use of traditional refrigerants which are environmentally harmful.Meanwhile,the issue of the new F-Gas regulation limits the utilization of the traditional refrigerants gradually in the near future.As a result,the revival of R744 is activated both environmentally and legally.China,as a developing market,the need for refrigeration systems in food retail area is substantial.Considering the supermarket refrigeration systems are characterized by the main source of the carbon footprint,it is of great importance to reduce their direct and indirect greenhouse gas emission.Normally,the performance of R744 refrigeration systems is competitive in cold region.This thesis investigates the integrated supermarket refrigeration for high ambient temperature region in Northern China.In this study,the performance of three state-of-the-art R744 transcritical refrigeration systems in Northern China has been discussed both theoretically and experimentally.The investigated systems includes the conventional booster systems(CB),the booster systems with parallel compression(PC)and the ejector supported booster systems with parallel compression(EJ).According to the experimental results,the enhancement of the COP between the CB and PC systems is 14.8% and the 6.9% when the temperature of the refrigerant flowing out from the gas cooler is 35? and 30? respectively.Concerning the performance of the EJ system,the COP is improved by about 2.2% compared to the PC system when the exit temperature at the high pressure side is 33?.However,the deterioration of the auxiliary compressors might degrade the performance of the EJ systems in some conditions.According to the simulation,the performance of PC and EJ is competitive when the ambient temperature is lower than 24? and 36?,compared the separated subcritical systems using R404 A.For systems integrated with AC units,the ambient temperature can no longer constrain the use of the R744 systems when it is lower than 30? and 40? for PC and EJ systems respectively.Consequently,the CB system is only recommended to be applied in the cold area,like Harbin and Changchun in Northeast of China.In some places not so cold,such as Yinchuan and Urumqi which are located in the Northwest of China,the PC system is advised.While for some other warmer places,mostly on Northern China Plain,the EJ system is a prior choice.