Abstract
The adoption of the EU F-Gas Regulation 517/2014 and the resulting development of the multi-ejector concept have led carbon dioxide to take center stage as the sole refrigerant (R744) in several applications. Therefore, a knock-on effect on the number of supermarkets relying on “CO2 only” refrigeration systems has been experienced. Additionally, a global consensus of commercial multi-ejector based R744 units is also intensifying as a consequence of both the promising results obtained and the other measures in force for environment preservation. Furthermore, the multi-ejector concept is expected to offer significant energy savings in other high energy-demanding buildings (e.g., hotels, gyms, spas) as well, even in warm climates. In this investigation, the evolution of R744 ejector supported parallel vapor compression system layouts for food retail applications was summed up. Furthermore, their technological aspects, the results related to the main theoretical assessments and some relevant field/laboratory measurements were summarized. Also, the experience gained in the adoption of the multi-ejector concept in transcritical R744 vapor-compression units aimed at other energy intensive applications was presented. Finally, the persistent barriers needing to be overcome as well as the required future work were brought to light.
Highlights
The implementation of the EU F-Gas Regulation 517/2014 [1] on fluorinated greenhouse gases (F-gases) has prompted the need to discontinue their use and substitute these working fluids with less environment-damaging alternatives
The adoption of a two-phase ejector in place of an expansion valve permits benefiting from two main energy advantages: (i) rise in refrigerating effect as the refrigerant enters the evaporator at lower vapor quality and enthalpy; (ii) decrease in compressor power input since the refrigerant is pre-compressed by theEnergies ejector from the evaporator pressure to the intermediate one (IP)
The system layout a low pressure (LP) accumulator to trap the liquid before compressors is mandatory, since liquid schematized in Figure 6 and adopted in a supermarket in the North of Italy simultaneously cannot possibly evaporate in the heat exchanger indicated as internal heat exchanger (IHX) D in Figure 5 [37]
Summary
The implementation of the EU F-Gas Regulation 517/2014 [1] on fluorinated greenhouse gases (F-gases) has prompted the need to discontinue their use and substitute these working fluids with less environment-damaging alternatives. This holds true for the sector involving high energy-demanding buildings (e.g., supermarkets, hotels, gyms), as the fulfillment of their refrigeration, cooling and heating (RC&H) needs causes significant indirect contributions to global warming as well. Its adoption is supposed to offer considerable energy conservations in other high energy-demanding buildings (e.g., hotels, gyms, spas) too, even in warm weathers In this investigation, the state-of-the-art multi-ejector based solutions for supermarkets and their technological aspects are presented. The remaining challenges requiring to be faced are summarized
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