Air as a refrigerant: Technology, opportunities, and limitations

Air, as a natural refrigerant, is attracting renewed attention in the wake of stricter climate protection requirements. Its major advantage lies in its environmental compatibility: air has no global warming potential (GWP ≈ 0), is non-toxic, non-flammable, and available worldwide. This eliminates many of the regulatory risks associated with other refrigerants.

Technically, air-cycle chillers are typically designed as Reverse Turbo-Brayton (RTB): The air is compressed, cooled, and then expanded through an expander, thereby generating low temperatures. This process can be supplemented with a recuperative heat exchanger, which allows the low-temperature level to be reduced even further. Two design types and applications can be distinguished:

• Applications requiring direct cold air: In these cases, the cold air can be provided directly by the refrigerant without the need for an additional heat exchanger. One example is the cooling of material samples with cold air for measurement purposes.
• Applications in which the cold is transferred from the air to the process via an additional heat exchanger, for example to a cooling fluid or a heat sink. A typical application area here is air-cooled chillers, in which conventional refrigerants or refrigerant mixtures cannot be used for technical reasons (e.g., very low temperatures) or regulatory reasons (e.g., exclusion of flammable refrigerants)—or a combination of both.

Modern compressor and expander technologies significantly improve the cost-effectiveness of such systems. Celeroton’s turbo compressors and expanders deliver high efficiency and, thanks to their high rotational speeds, a very compact design. Thanks to contactless gas bearings, the machines also operate oil-free and wear-free. This is particularly advantageous for refrigeration processes and applications with high purity requirements.

One interesting area of application is the semiconductor industry. In chip manufacturing, stable and extremely low temperatures are required for lithography systems, etching processes, wafer cooling, and precise process stabilization. At the same time, the highest standards of purity, reliability, and operational safety must be met. Air-based refrigeration systems offer advantages here, as they do not use flammable or environmentally harmful refrigerants, and oil-free turbo compressors minimize contamination risks. Celeroton’s compact turbo compressors and expanders also enable space-saving cooling systems with high power density—a key factor in modern semiconductor manufacturing facilities and cleanroom environments.

Other applications can be found in cryogenic technology, such as in the food, pharmaceutical, and medical industries, as well as in IT, telecommunications, and electronics manufacturing. Air is also used as a refrigerant in the chemical industry and in environmental and energy technology, as it is leak-safe, non-flammable, and complies with the latest regulatory requirements.

Compared to traditional two-phase refrigerant cycles, air-cycle chillers are often less efficient because air remains in a gaseous state throughout the process, requiring significant compression work. As a result, these systems tend to be larger and heavier. However, they can offer economically attractive solutions for a temperature range of approximately -50 to -120°C, combined with high safety requirements and GWP = 0 requirements. Modern components such as multi-stage compression, heat recovery, and highly efficient turbo compressors and expanders improve the coefficient of performance.

Air is not a substitute for all traditional two-phase refrigerant processes, but it is a robust, safe, and climate-friendly alternative for specific applications. Especially in the semiconductor industry, modern air-cycle chillers open up new possibilities for clean, safe, and high-performance process cooling without negatively impacting global warming potential. Thanks to Celeroton’s modern turbo compressors and expander systems, such systems become more compact, efficient, low-maintenance, and economically attractive.

Do you have any questions about this topic or would you like to discuss possible solutions? Please don’t hesitate to contact us at moc.notorelec@ofni or +41 44 250 52 20!