Recently, there have been consistent research efforts to improve fuel economy as response to the depletion of fossil fuels and global warming. With regard to construction equipment (i.e., one of the most energy-wasting types of machinery), fuel economy improvement through advancement in engine technologies has reached its limit. Hence, we conducted a study in which a waste heat recovery (WHR) system was incorporated into a construction machine to improve the energy efficiency. Excavators are one such machine where significant portions of the fuel-generated energy are not utilized effectively for work but instead wastefully discharged to the atmosphere.