In this research, the technique of presuming how far degradation of the air conditioner affects the amount of energy consumption, when the building is used is established theoretically. Therefore, the fluctuation tendency of the amount of energy consumption across the ages of middle-scale office buildings are clarified first, and it presumes about the factor. Further, the calculation technique of degradation rate of the air conditioner is created theoretically, and the degradation rate across the ages of each building is computed. Moreover, the relation between preservation expense and degradation rate is analyzed. Finally, a case study is performed, the operation expense of an air-conditioning system is computed, and the economics of the system is evaluated.
