Conference Agenda

Refrigeration cycles operating below −50 °C are highly inefficient and rely on refrigerants with high global warming potential. This inefficiency is primarily due to limited technological advancements and a lack of comprehensive studies on suitable refrigerants for ultra-low temperatures. To address this gap, this article aims to analyze the experimental behaviour of a cascade compression cycle for ultra-low temperature refrigeration. The refrigerants analysed are R290 in the high-temperature stage and R170 in the low-temperature stage. These refrigerants have been compared with the R404A/R23 pair, which is commonly used in the sector, and the R448A/R170 pair. The results indicate that the R290/R170 pair provides superior performance in terms of the coefficient of performance. A Total Equivalent Warming Impact analysis demonstrates its environmental advantages. It also achieves the best results in compressor volumetric efficiency and discharge temperature.

This paper explores the challenges of selecting appropriate ambient temperatures in the context of rising global temperatures and analyses the impact on plant performance. The first section examines whether planning for worst-case temperature scenarios is the most effective approach, considering regional variations and future climate projections. The second section investigates plant performance in high ambient temperatures, using real-world data from cold chain facilities and comparing it with theoretical predictions.

By reviewing electrical consumption, store temperatures, plant operational conditions and coefficient of performance, the paper identifies deviations between predicted theoretical and actual performance in three key locations including the South West, Midlands, and Scotland. This analysis offers insights into temperature management, energy consumption, and the implications of high ambient temperatures on plant efficiency.

This work experimentally assesses R472B as a lower-GWP alternative to R23 in a two-stage cascade ultra-low temperature refrigeration system. First, the pull-down performance from 15, 20 and 25 °C down to –70 °C is analysed. Then, the hysteresis operation with set freezer temperatures of –70, –60, and –50 °C is studied. The pull-down time was higher for R472B compared to R23, with a time difference from 23 to 40 minutes. Regarding the hysteresis operation, the lowest energy consumption for all the tested conditions was achieved by R472B, being 8.4 to 17.5% lower than R23. The cooling capacity of R472B was 9.4 to 26% lower at –70 and –60 °C, and up to 13% higher at –50 °C. COP was comparable at –70 and –60 °C, and at –50 °C, R472B COP was up to 15.6% higher. The environmental analysis of the hysteresis operation shows that equivalent CO₂ emissions can be reduced by 65% when using R472B instead of R23.