Overall Energy Efficiency of Lubricant-Injected Rotary Screw Compressors and Aftercoolers

This paper shows how to analyze the overall energy efficiency of two typical equipments of compressed air system: lubricant-injected rotary screw compressors and aftercooler. Firstly, air power, a proposed effective tool of weighing energy, is introduced as the quantitative standard of energy in compressed air. Then, compression process of lubricant-injected rotary screw compressors for air production is analyzed deeply and the state change of compressed air is discussed in detail. Compressed air's air powers in the one-stage compression air system including one- stage compressor, intercooler, and aftercooler are discussed particularly. After discussion on the compressor's adiabatic and isotonic efficiencies, the efficiencies of compressor and aftercooler are defined with air power and their overall energy efficiency is proposed as the final energy- conversion efficiency. The efficiency analysis methods discussed in this study will be greatly helpful to an energy-saving equipment selection and energy assessment for pneumatic system.