Compressor Efficiency Definitions

Many standard efficiency denitions exist that qualify the mass flow and power performance characteristics of a compressor. These dierent definitions are often used interchangeably throughout the compressor industry, although each is based on fundamentally different assumptions. This often results in incorrect comparisons between compressors oered by different companies, which precludes the customer from obtaining a fair and accurate assessment of their compressor needs. Here, we present a brief description of some efficiency definitions to aid in understanding differences between them. To do so we rst introduce a simple theoretical thermodynamic model of the compressor, and characterize its states during operation. Theoretical mass-flow equations are then presented, and theoretical compressor work are power are obtained. Next, power definitions, taken from standard thermodynamics texts and industry usage, are defined and discussed. Finally, these powers are used to dene compressor eciencies and recommendations are provided regarding their use, including which efficiency definitions are used by Vairex when characterizing compressors