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migrated to microchannel heat exchangers: these type of heat exchangers improve system efficiency (reducing the indirect environmental effect) while at the same time reducing refrigerant charge (reducing the direct effect). Compressors represent an area of great improvement. Manufacturers are moving from single stage compressors to multi stage, and to variable speed, with significantly improved average energy efficiency. Finally, the introduction of new refrigerants gives an opportunity to introduce additional optimisation in the area of expansion and cycle control, discharge temperature control, heat exchange optimisation with regards to temperature glide of refrigerant mixtures. A final trend can be observed in the area of alternative energy sources, particularly for truck and trailer. More and more non-diesel solution are being introduced. Eutectic, diesel free solutions are used in small refrigerated vans, as are various systems where nitrogen or CO2 is injected into an open loop heat exchanger and exhausted to atmosphere. Other alternatives are for example battery powered systems and compressed natural gas engines. 6.4 Options for existing equipment 6.4.1 Trucks and trailers Studies analyzing field alternatives to R-404A and HFC-134a are continuing, looking at both natural and non-natural solutions. Retrofit of an existing R-404A system with natural solutions (such as R-290 or R-744) appears unlikely now and in the future, mainly because of the very substantial conversion system change necessary. Retrofitting R-404A with R-452A is much simpler and is already happening in the marketplace in Europe. The solution is a near drop-in; the GWP is significantly reduced and performance almost maintained. With the progress of F-gas regulation it is reasonable to expect that availability of R-452A will be reduced, and new alternatives may be required. New refrigerants R-448A and R-449A stand out as lower GWP (approx. 1,400) options, requiring system changes with various degree of complexity (typically addition of liquid injection to limit discharge temperatures). 6.4.2 Containers Similar to truck and trailer, retrofit of an existing, R-404A or HFC-134A system with a natural solution (such as R-290 or R-744) appears unlikely now and in the future due to the different design and complexity of the system changes. Retrofitting R-404A with R-452A is much simpler and is already happening in the marketplace. In a similar way, trials on retrofitting HFC-134a systems with R-513A are ongoing. One manufacturer offers HFC-134a based reefer systems which can be used for operation with R- 513A (MCI, 2017). 6.4.3 Ships Ships are in operation for 30 years on average. Merchant and cruise ships are among the newer equipment. The average age of a merchant vessel has been decreasing from 18.9 years in 2008 to 16.7 years in 2012 (ISL, 2012). The number of cruise ships and their size has about doubled in the last decade (ISL, 2011). HCFC-22 has been the dominant refrigerant in many marine applications and is still used in the majority of reefer ships. For most countries, despite their systems often incurring leaks, there is no difficulty in refrigerant supply and they continue to be replenished and used. 126 2018 TOC Refrigeration, A/C and Heat Pumps Assessment ReportPDF Image | Heat Pumps Technical Options
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