Stewing about terminology used in the havc/r industry that isn't consistent or precise. Perhaps the Prof is thinking too much, and needs to find a beer...

Consider the term "compression ratio". It is a volumetric ratio defined as the swept volume to the clearance volume, and most often associated with internal combusion engines. And as most car enthusiasts know, a compression ratio of 8 to 10 or so is common for gasoline engines, and approx double that for diesel engines.

But it seems many (if not most) in the hvac/r industry use this term as a pressure ratio to describe the ratio of discharge pressure to suction pressure across a compressor, using absolute pressure units. For example, many in the industry will say that an R-22 compressor operating at a 240 psia discharge pressure and a 60 psia suction will be operating at a "compression ratio" of 240 / 60 or 4 : 1. Of course, this cannot be the case, since swept volume to clearance volume in a compressor is fixed, and has nothing to due with pressures. The correct term to use here is simply "pressure ratio".

So why are there so many (incorrect) references to "compression ratio" in the hvac/r industry. Prof diatribe #107.

The Prof also has a problem with the term "thermostatic expansion valve", which suggests a valve that controls constant temperature...