The objective of this research project is to select and qualify a new refrigeration fluid for combined use as a lubricant for compressor lubrication and as a heat transfer fluid in a CO2 sublimator. Such a hybrid fluid is a prerequisite for implementing a closed-loop, low-GWP sublimation refrigeration cycle as a replacement for existing high-GWP cold-vapor refrigeration cycles for the temperature range down to -80 °C. The project idea is based on the intention to find a fluid that combines the advantages of compressor lubrication and heat transfer in the sublimator. It must be determined which fluid best meets these requirements. A fluid with good solubility for CO₂ at low temperatures could be advantageous, as it would reduce viscosity and improve flow behavior in the sublimator. Additionally, however, the viscosity must allow for sufficient lubrication of the compressor under CO₂ compression conditions. On the other hand, while a fluid with low CO₂ solubility would not contribute to improved viscosity reduction in the sublimator, it would, in contrast, offer advantages in terms of compressor lubrication. There are numerous applications requiring cooling temperatures below -50 °C. Examples of this include applications in the fields of environmental simulation, medical and pharmaceutical technology, cryopreservation, freeze-drying, and food technology. Successful completion of the research project will lay an important foundation for the operation of closed-loop sublimation refrigeration systems, enabling the replacement of R-23 with the environmentally friendly refrigerant CO2 in a range of applications. The EU refrigeration market is currently experiencing a shortage of fluorinated refrigerants with high GWP values (GWP = Global Warming Potential). This is accompanied by rising prices, which, in the case of the cryogenic refrigerant R-23, have already reached several hundred euros per kilogram. This situation is not expected to change, as the EU F-Gas Regulation, which took effect in 2015, established emission reduction targets that are binding for the coming decades. This is increasing the pressure on affected manufacturers to find alternative refrigerants for their applications. For the temperature range required for cooling below   -50 °C, there are currently no non-flammable refrigerant alternatives. CO₂ sublimation represents a viable option for achieving cooling temperatures below -50 °C using a non-flammable refrigerant.