Recommended by the IIR / IIR document

High efficiency cold sauna on -115°C with only air as a refrigerant.

Number: 0001

Author(s) : FRANK T.


In September 2019 Refolution built the first cold sauna for COOLINN with only air as a refrigerant and several other innovations. The refrigeration technology is an air cycle refrigeration machine with an oil free air mounted turbo-expander from Mirai Intex. The chamber is designed with industrial standards with hook connected PU-foam panels with integrated vacuum shield and a second insolation shield for minimum transmissive thermal load. The system can run permanently on low temperatures without the need of defrost or even worse warming up the complete chamber. Between the last two lock downs the chamber was constantly for 6 months at temperatures of -115 °C during daytime and -40°C at nighttime. The light installation is realized by LEDs which can be turned on and off even at temperatures of -130°C. The chamber is designed with a double insulated floor and a sloping base for a better drainage for cleaning during warming up. It has a special air distribution system for uniform air flow in the chamber as well as an innovative dehumidification system which results in a dew point of 15 K below the room temperature and does not require defrost, thus reducing the thermal efficiency of the cold room. All innovative features combined revolutionize the cold sauna market resulting in the best experience for customers. With only air as refrigerant and permanent visual and audio monitoring of the customer inside the cold room this is the safest and cost-effective solution for cryotherapy.
In 2020 Refolution performed an energy analysis of refrigeration systems for applications at temperature between -40°C to -110°C and demonstrated that air refrigeration is one of the most efficient solutions for this temperature applications at the current state-of-the-art. For continuously improvement of the systems efficiency, a heat recovery system was added that allows COOLINN to use the waste heat from the air cycle machine to dry customers after sports or on rainy days and heat the complete lounge on cold days.

Available documents

Format PDF

Pages: 5


  • Public price

    20 €

  • Member price*


* Best rate depending on membership category (see the detailed benefits of individual and corporate memberships).


  • Original title: High efficiency cold sauna on -115°C with only air as a refrigerant.
  • Record ID : 30028998
  • Languages: English
  • Source: Cryogenics 2021 online. Proceedings of the 16th IIR International Conference, October 5-7, 2021.
  • Publication date: 2021/10/05
  • DOI:
  • Document available for consultation in the library of the IIR headquarters only.


See other articles from the proceedings (34)
See the conference proceedings