Experience with ejectors implemented in a R744 booster system operating in a supermarket

The average energy use of European supermarkets is in the range of 300 to 600 kWh/m2 (Energy star, 2008; Arias, 2005). Around 50% of the energy is used to the refrigeration equipment which provides cooling and freezing capacity for the display cabinets and the cold / freezing storage rooms. Most of the current refrigeration systems are applying HFC 404A as the working fluid. According to the survey in the latest IPCC/TEAP Special Report (2007), the average annual leakage rates of existing European HFC supermarket units are between 15 and 20% of the total refrigerant charge. On a global perspective the commercial refrigeration leakage rates are around 30%, while HCFC 22 is the most common refrigerant. Therefore, effort should be given to identify alternative refrigerants which are able to improve the energy efficiency compared to current HFC solutions. Preference should be given to natural working fluids, since their long term environmental impact can be foreseen and they minimize the direct GWP contribution.
Currently there are more than 2000 commercial refrigeration system, applying carbon dioxide (R744), mainly located in Central- and Northern Europe. The efficiency challenge related to ordinary R744 booster systems operated at high ambient temperatures (Finckh, 2011) can be overcome by an improved system design as described in this paper. As one possible example, an enhanced R744 commercial refrigeration system with parallel compressor technology and ejector support is described, as implemented in a large supermarket in the region of Fribourg (Switzerland) during summer 2013. First measurement results are analysed and evaluated.