Due to the F-Gas Regulation, there is currently a shift toward natural refrigerants in refrigeration systems across Europe. Because of its physical properties, CO2 offers good conditions for utilizing the energy generated during expansion in the refrigeration cycle. As an alternative to an ejector, expansion machines can be used to harness this energy. As part of the preliminary research project VF160025, “Reduction of Expansion Losses in Refrigeration Systems,” the potential of such an expansion machine was investigated. In this project, electrical energy extraction will be examined in detail as part of the project cluster focused on converting the turbine’s energy into electrical current via a generator. This solution offers the outstanding advantages that the combination of turbine and generator can be implemented in a semi-hermetic design with a technically sealed electrical interface, and that the rest of the refrigeration cycle and its process control are affected only minimally, if at all.

The braking power generated during the control process should be effectively utilized to increase the coefficient of performance of the refrigeration system, taking economic factors into account. The following aspects should be investigated:

• Developing a reliable and cost-effective control system for the generator
• Measuring the dynamic characteristics as a function of rotational speed under the given boundary conditions, particularly in a CO₂ atmosphere
• Sealing the expansion turbine with a technically airtight electrical interface
• Universal utilization of the decoupled power component

As part of this project, an electrical power extraction method is being developed that enables the operation of an expansion turbine for general refrigeration applications (with a focus on supermarket refrigeration) and offers the following advantages:

• independent operation of the expander and compressor without a mechanical shaft
• variable speed range of the expander synchronized with the cooling load profile
• semi-hermetic design for the expander and compressor
• use of power extraction independent of the refrigeration cycle through the following alternatives:
  • in-cycle electrical auxiliary compressor drive
  • universal grid power feed-back coupling
  • variable, cost-reduced braking resistor operation

Ultimately, the supplementary process for electrical power extraction is intended to enable the use of CO2 expansion turbines in general refrigeration and heat pump applications.