This paper describes retro commissioning of a standard commercial office building in Japan. The owner's expectations for retro commissioning are realization of energy and cost savings, and controlling the increase in electric power demand, while continuing use of most existing equipment, and maintenance of high efficiency operation. First, the performance of the existing equipment was checked using the BEMS during retro commissioning program phase. Next, optimal selection of a system and heat source equipment was performed using the simulation in the design phase. Furthermore, the verification of the performance of the refrigeration machine installed was carried out as a Functional Performance Test. And the economic effect by a repair work was verified during the operation phase. The simple payback of the project was about six years
