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As described in detail in the 2014 RTOC Assessment Report, R-744 is a possible alternative refrigerant for both containers and truck and trailers. The challenges are: high pressure and lower performance in high ambient temperature. One manufacturer has released in Europe field trial quantities of a trailer closed loop solution based on CO2. Specifically, a UK supermarket chain has continued carrying out trials of an R-744 refrigerated trailer since 2013 (UTC, 2013). They revealed that they have subsequently acquired a second R-744 trailer that can operate at different temperatures and this was joined by a third in 2016. Trials of R-744 trailers with two large supermarket chains in Europe are continuing (CP, 2016). The efficiency of R-744 continues to prove higher than incumbent refrigerants at low to moderate ambient, but inferior, when compared to R-404A, at medium to high ambient temperatures (UNEP, 2014). For this reason, the first truck and trailer commercial applications of R-744 are located in moderate ambient regions in small numbers. R-744 has been implemented using a semi-hermetic dual stage reciprocating compressor, where the issue of high pressures can be managed more easily. R-744 open shaft compressors have technological challenges in the transport refrigeration pressure range and continue to be unavailable today. 6.3.1.2 Safety considerations Hydrocarbons continue to be examined due to their superior thermodynamic properties, but the possibility of leakage of the flammable refrigerant inside the box and other failure scenarios present a safety issue to be mitigated by design operation and servicing procedures. Currently, no commercial solutions with hydrocarbons in transport are available. However, the number of relevant scientific studies presented at recent conferences (e.g. IIR Gustav Lorentzen series, etc.) to manage flammability risk on A3 and A2L fluids, is testimony of significant research and development going on in the area of flammability mitigation in transport. One relevant paper describes the successful field test results of a small truck unit using HC-290 in South Africa (Colbourne et al., 2016). Other papers studied the energy efficiency of different replacement options in container and truck/trailer (Finckh et al., 2016; Poolman et al., 2016). 6.3.2 Containers 6.3.2.1 Non-flammable solutions R&D activity is continuing to assess non-flammable (A1) lower GWP solutions that could replace the so far dominant HFC-134a and R-404A. R-513A, R-513B, and R-456A are potential candidates for HFC-134a replacement, and R-513A seems to attract most interest. One manufacturer announced a test of 100 units with R-513A together with 2 major shipping lines (MCI, 2017); shipping lines ordered approximately 10,000 R-513A compatible reefer units for potential later retrofit (MCI, 2018). R-744 has been field-tested in container refrigeration applications since 2011. Its non-flammable characteristics make R-744 an attractive option, but the gap in efficiency at high ambient temperatures and the limited component supply base are limiting its market penetration. The efficiency of R-744 continues to prove higher than incumbent refrigerants at low and moderate ambient, but inferior at medium to high ambient (UNEP, 2014). In the last 2 years, at least three shipping lines have purchased or leased a total of approximately 2,200 units operating with R-744 (Carrier, 2018). 122 2018 TOC Refrigeration, A/C and Heat Pumps Assessment ReportPDF Image | Heat Pumps Technical Options
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