Text 2-8: Determine the power rating for the electric motor driving the compressor for the air required to operate a factory's pneumatic tools (all air consumption rates are of free air). Assume that leakage and unintended use (for personal cooling, perhaps) is 10% of the pneumatic tool usage. Approximately 80 cfm extra capacity is needed for future expansion. Pneumatic tools require 70 psig at the tool, and the pressure drop in compressed air lines is 10 psig. The compressor efficiency is 80%, and the compressor intake is located inside the air-conditioned factory. Specify a compressor type.
Tool Number Air consumption, cfm Load factor, %
8" grinder 10 70 50
Chipper 10 15 50
Hoist 2 100 10
Blowers, chucks, vises 30
Text 2-9: Estimate the power reduction and electrical energy cost savings if outside air is provided to the compressor intake of Problem 2-8 in the wintertime, assuming 1000 h/yr wintertime operation and $0.08/kWh electricity price.
Text 2-10: Estimate the energy saving if the discharge compressed air of Problem 2-8 were cooled by make-up water that needed to be warmed for use in washing printed circuit boards, assuming that heating would otherwise be 2000 hr/yr in a gas-fired heater and $5/106-Btu gas price.