Both the energy efficiency of refrigeration systems and heat pumps, as well as the use of alternative refrigerants, are influenced by the choice of lubricant and the amount of lubricant used in the respective systems. The oil required for compressor lubrication enters the refrigerant cycle and, in most cases, reduces the cooling or heating performance of the system. In addition, foam formation and oil solubility in the refrigerant can lead to a reduction in viscosity and consequently to insufficient lubrication or complete compressor failure, which in turn negatively affects the energy efficiency, service life, and operating limits of the compressor. Compared to the fluorinated refrigerants commonly used today, hydrocarbon refrigerants, such as propane (R290), in particular show increased problems related to insufficient compressor lubrication. The question of the “right” oil and refrigerant–oil mixture (ROM) has not yet been sufficiently investigated or validated in practical applications and, in addition to refrigerant flammability, represents a further obstacle to the widespread use of R290 in refrigeration and heat pump systems. The objective of the project is to determine an optimal and operationally reliable refrigerant–oil combination for an efficient supermarket refrigeration/heat pump system using R290 and thereby reduce the two major barriers to the introduction of R290 in stationary refrigeration technology. A holistic and model-based consideration of the refrigeration cycle, including refrigeration components and the refrigerant in combination with lubricants (oil), is therefore necessary. During the course of the project, the missing material data for refrigerant–oil mixtures must first be determined. In order to validate the dynamic refrigeration cycle simulation software (models, material properties, ROM, components) and to determine the energetic and long-term influence of refrigerant–oil mixtures on components, particularly compressors and the system in application, the setup of a real system under laboratory conditions is required.

The objective of the project is to determine an operationally reliable and efficient refrigerant–oil combination for a refrigeration/heat pump system using R290 and thereby reduce the two major barriers to the introduction of R290 in stationary refrigeration technology. In order to achieve this objective, the following work will be carried out by the individual project partners. The lubricant manufacturer KLÜBER is responsible for the selection, development, and approval of the optimal oil. For this purpose, commercially available oils will first be investigated in order to subsequently develop a new oil. The oil manufacturer works closely together with ILK and the compressor manufacturer BOCK. BOCK provides the compressors for the test refrigeration system, performs analyses on them, and ultimately approves both the compressor and the oil in combination with the refrigerant R290. The research institute ILK determines the material properties of the refrigerant–oil mixtures, for example to investigate the mixing behavior of the fluids. In addition, the institute provides the required material data of the mixtures for further calculations in dynamic models, determines polynomials for calculating the oil concentration in the refrigerant, and performs performance tests on the compressors. The dynamic models are developed by COOLPLAN with support from HRW and integrated into a software tool in order to optimize the efficiency of the refrigeration system through simulation. Furthermore, HRW validates both the material data and the software tool using a test refrigeration system that is designed by COOL EXPERT and integrated into an existing test rig at HRW. In addition, COOL EXPERT develops an oil sensor and carries out its validation.

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