The traditionally used CFC process fluids have been shown to be harmful to the ozone layer. The new fluids do not destroy the ozone, but there are other problems. Conventional compressors require a fluid which works with the lubricating oil, and this restricts the choice of process fluid.
A high speed compressor with gas bearings does not need lubricating oil, and this makes it possible to choose a really environment friendly process fluid.
Two prototypes of refrigerating devices have been built at LUT. The first (1994) was equipped with a 300 W high speed compressor and asynchronous motor. The compression is made in two stages in order to achieve optimal efficiency for the needed compression and the rotational speed is over 200 000 rpm. The impellers of a high speed refrigerator compressor is very small.
The second (2004) test facility is a 1 200 W compressor with a synchronous motor.