Ammonia, one of the oldest refrigerants, still attracts a lot of attention in the refrigeration industry and is to stay as one of the most widely used refrigerant. This is because ammonia is a natural refrigerant with the least impact on the environment and has excellent thermal properties thus offering systems with high COPs. The main drawback of ammonia, however, is toxicity, smell and flammability, thus most ammonia refrigeration systems are of indirect type using secondary refrigerants. In order to enhance safety and reliability of ammonia refrigerating systems, reduced refrigerant charged systems were developed. Oil miscible with ammonia was developed to enable use of direct expansion systems and combined with compact heat exchangers, refrigerant charge was drastically reduce as compared to flooded systems. An electronic expansion valve improved the efficiency of the system while a semi hermetic motor minimized refrigerant leakages. This paper reports on the development of ammonia refrigeration systems with optimized refrigerant charge.
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