Overview of the development and status of carbon dioxide (R-744) refrigeration systems onboard fishing vessels.

• Main refrigeration systems in fishing vessels are based on R-22 and R-717. • There are significant developments in R-744 refrigeration systems. • The number of R-744 refrigeration units in fishing vessels has been increasing. • There is a lack of scientific efforts/studies on R-744 systems in fishing vessels. Globally, most fishing vessels still use the ozone-depleting and climate-harmful R-22 in their freezing and refrigerated seawater (RSW) systems. However, in some regions, the natural refrigerant ammonia is the preferred refrigerant. Another natural refrigerant, carbon dioxide (R-744), is becoming a viable option and is increasingly used onboard. This option will not exclude ammonia, but rather will be a good alternative to it to meet the demand for different cooling/freezing needs in post-R-22 systems. There are currently major developments in R-744 refrigeration technology that are widening the potential applications of R-744. These include compressors with larger capacities, more energy-efficient components, system designs with lower freezing temperatures and integration of heat recovery and thermal storage. This paper provides a review of the development of refrigeration systems with R-744 onboard fishing vessels. It includes a description of the commonly used cooling and freezing methods and of the development in R-744 refrigeration technology, especially within the system and component design, capacity and performance. It also includes the current status of R-744 refrigeration technologies in fishing vessels. Although there are limited publications on R-744 systems for fishing vessel applications, the review shows positive prospects of utilizing R-744 and further research and innovation within this topic is recommended. [ABSTRACT FROM AUTHOR]