U.S. refrigeration scientists have designed and evaluated an CO2 (R744) multi-temperature refrigerated transportation container capable of maintaining an efficiency similar to, or better than, traditional HFC technology, even in high ambient temperatures up to 50°C (122°F).
The prototype container was designed by Senior Research Engineer Neal Lawrence, Chief Engineer Stefan Elbel, and President Pega Hernjak, all of Creative Thermal Solutions, Urbana, Illinois (U.S). Elbel and Hrnjak are also Research Assistant Professor and Research Profressor, respectively, at the University of Illinois at Urbana-Champaign.
Elbel presented the team’s findings at the 2020 Gustav Lorentzen Conference on December 9, from the paper, “Advanced R744 Technology Applied to a Multi-Temperature Refrigerated Container.”
In ambient temperatures from 25°C up to 50°C (77°F to 122°F) the container prototype achieved:
- A medium-temperature capacity of 5.4 to 3.4kW (1.5 to 0.97TR),
- A low-temperature capacity of 4.1 to 2.3kW (1.17 to 0.65TR),
- A coefficient of performance (COP) of 1.60 to 0.75.
When comparing the results to an R404A single-temperature container at 40°C (104°F) ambient temperature, the R744 prototype achieved an 18% better COP.
To achieve these results at high temperatures, the team used a number of CO2 enhancement technologies, including low-temperature booster compression, multistage transcritical compression with intercooling, internal heat exchange (IHX), and expansion work recovery using an ejector.
The team looked at which of the enhanced components made the biggest contribution to the increased COP, and found that the IHX contributed 31%, followed by the low-temperature compressor (24%), and the ejector (16%).
The team predicts that it would be possible to further improve the COP by enhancing the ejector, low-temperature compressor and IHX performance, and estimated that an additional 5-10% increase is achievable.