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.