The rotary design of refrigeration compressors does not include which of the following?

The rotary design of refrigeration compressors typically involves moving parts that create a vacuum to draw in refrigerant and then compress it, utilizing mechanisms that rely solely on rotational motion. In this context, options such as rotating vane, helical rotor, and helical screw are all designs that feature continuous rotation and are classified under rotary compressors.

Rotating vane compressors use vanes that move in a circular motion inside a cylindrical chamber. Helical rotors rely on screw-type designs that compress refrigerant as it moves through the rotor system. A helical screw compressor uses two interlocking helical rotors to sequentially compress the refrigerant, also functioning entirely on rotational dynamics.

In contrast, a piston-based design is categorized as a reciprocating compressor. This mechanism relies on the linear movement of pistons within cylinders to compress the refrigerant, which is fundamentally different from rotary designs. Therefore, a piston cannot be included in the rotary design category, making it the correct answer to the question.