Overfed evaporators and parallel compression in commercial R744 booster refrigeration systems - An assessment of energy benefits.

The entry into force of the EU F-Gas Regulation 2014 pushes European Countries to use natural refrigerants. Carbon dioxide (R744) is one of the most promising long-term alternatives to the currently employed refrigerants in commercial refrigeration. On the other hand, the use of CO2 supermarket refrigeration systems in warm climates requires specific technical solutions to make them competitive with conventional HFC-based plants. In the European market, different layouts have been currently proposed, which have been mainly derived from the basic booster configuration. In this paper, the performance of a commercial CO2 refrigeration solution employing medium temperature (MT) overfed evaporators, a CO2 refrigeration configuration using parallel compression and the system which combines both of the previously technologies were theoretically compared. Three different warm climate locations were selected, i.e. Rome (Italy), Valencia (Spain) and Seville (Spain). The results showed that the benefits deriving from a higher evaporating temperature in the MT display counters, allowed by overfed evaporators, outweighed those related to parallel compression. Furthermore, the investigated R744 refrigerating plants performed an annual energy saving ranging from 2.9% to 12.3% over a R404A multiplex refrigeration system. The use of a de-superheater on the part of the combined solution led to an additional drop in the annual electricity consumption by 2.3-2.6%.