Air as Next-Gen Refrigerant Going Natural: Is Air the Future of Refrigeration?

| Editor: Dominik Stephan

The current F-gas regulation forces plant operators and planners to rethink their processes: Alternatives to conventional refrigerants with their often high greenhouse gas potential are needed. But sometimes the good is so obvious: a new process with ambient air wants to exceed the requirements of the industry.

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Cooling with air: The cryoblizzard proved its worth during the retrofit of a freeze dryer.
Cooling with air: The cryoblizzard proved its worth during the retrofit of a freeze dryer.
(Source: Hof Sonderanlagenbau; © - [M] Frank)

Pharmaceuticals, biotech production or chemical industries: The entire industry is currently in upheaval due to the social and political rules and regulations with regard to climate change, and many operating companies are unsure. This concerns refrigeration in particular, as the established technologies established in this field are increasingly restricted through political regulations and bans and through shortages. For plants with a service life of over 30 years, operating companies focus especially on the future-proof design, reliability and quality of their plants. Energy efficiency, safety, selection of components, documentation and durability are also crucial factors that force engineers to consider alternative approaches.

Could e.g. air be used as an alternative refrigerant? Its climate warming potential (GWP) at least is zero. Oliver Fleischer, responsible for the Development of Refrigeration Technology and Service Manager at Hof Sonderanlagenbau, would agree: "Air is available, non-flammable, non-toxic and poses no risk of suffocation. Air has no GWP and is therefore not subject to the F-Gas Regulation or other directives. That is the future!”


Thus, the German engineering technology specialist focuses on the utilisation of this particular mixture of gases with their Cryoblizzard central cooling and refrigeration technology. This particular approach proved its worth in the retrofit of a freeze drying plant from 1998. The plant is a freeze dryer with a batch capacity of 40 kg for insulin production. Before the retrofit, refrigeration was achieved with two refrigeration sets, each with 12 kg of the R404A (GWP 3922) refrigerant. The process plant was controlled by a Siemens S5 control.

Better Safe than Sorry

With the new process, refrigeration consists of redundant cold air machines which are switched to a central primary tank in a modular system. The primary tank supplies the consuming units such as adjusting shelves, ice condenser or blast freezer directly with the refrigerant medium and can therefore provide large capacities with homogeneous temperature distribution within a very short time. The primary tank means that the cooling water and the power consumption remain constant and that no load peaks occur during the supply. The cooling water consumption was reduced by half with the retrofitting. The cold air machines from Mirai Intex are chillers which operate with air as a refrigerant using the counter-clockwise Joule process.

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The maximum overpressure in the machines is 3 bar(a) and can be compared to that in a bicycle tyre. This makes these machines particularly safe and environmentally friendly. No special requirements result from this with regard to the machine room, employee training and recurrent testing. In addition to this, air as a refrigerant is free and always available, has a GWP of 0 and is therefore not affected by any regulations.

New Ways for Refrigeration

“We knew that, as an innovator, we have to tread new paths for our customers", Fleischer explains. "The advantage of air as a refrigerant is obvious!” The refrigeration circuit is driven by an air-bearing supported, oil-free turbo compressor–expander unit from the brand Mirai-Intex which runs with up to 88000 rpm with virtually no wear. The refrigeration medium is cooled in a heat transfer unit integrated into the chiller. The air heated in this way is aspirated by the turbocharger and compressed. Then the energy in the gas chiller is dissipated to the environment and cooled down. In an inner heat transfer unit, the recuperator, the air is strongly cooled down and then relaxed for effective use in the expander. The work is returned to the compression. The energy is now absorbed through heating of the air in the cold medium/heat transfer unit. After the air in the recuperator has been heated again, it is aspirated by the compressor and the cycle starts again.

The modular plant design means that the capacity can be scaled up or down, allowing it to be adapted from a small freeze dryer to a central cooling system for complete factories. With Cryoblizzard, existing plants can be retrofitted and new plants can be implemented. Hof has developed a future-proof solution for freeze drying and blast freezing which is not only safe for employees and the environment, but also sets new standards with regard to the quality and availability of the application.