A method of controlling a network system, the method comprising: - recognizing power information including information about an on-peak time period and an off-peak time period and recognizing time information regarding an operation of an electric product, the time information including a desired operation time period; - estimating power information of the electric product in the desired operation time period, the power information of the electric product including at least one of a power consumption amount and a total electricity charge, - determining whether the estimated power information is equal to or higher than a predetermined reference value; - if it is determined that the estimated power information is equal to or higher than the predetermined reference value, determining whether the user wants to change the operation time period of the electric product; - if it is determined that the user wants to change the operation time period of the electric product, determining whether an operation mode of the electric product includes a plurality of time-series processes; - if it is determined that the operation mode of the electric product includes a plurality of time-series processes, determining whether a portion or all of the operation time period is included in the on-peak time period when the electric product is operated in the operation mode; - if it is determined that a portion or all of the operation time period is included in the on-peak time period, determining whether a last process of the plurality of time-series processes should be performed in the on-peak time period; and - if it is determined that the last process of the plurality of time-series processes should be performed in the on-peak time period, operating the electric product in an energy-saving operation mode for reducing an energy-related value based on the recognized power information and the time information, wherein the operation of the electric product is changed so that only the last process or some processes including the last process are performed in the on-peak time period and the estimated power information is equal to or lower than the predetermined reference value. - recognizing power information including information about an on-peak time period and an off-peak time period and recognizing time information regarding an operation of an electric product, the time information including a desired operation time period; - estimating power information of the electric product in the desired operation time period, the power information of the electric product including at least one of a power consumption amount and a total electricity charge, - determining whether the estimated power information is equal to or higher than a predetermined reference value; - if it is determined that the estimated power information is equal to or higher than the predetermined reference value, determining whether the user wants to change the operation time period of the electric product; - if it is determined that the user wants to change the operation time period of the electric product, determining whether an operation mode of the electric product includes a plurality of time-series processes; - if it is determined that the operation mode of the electric product includes a plurality of time-series processes, determining whether a portion or all of the operation time period is included in the on-peak time period when the electric product is operated in the operation mode; - if it is determined that a portion or all of the operation time period is included in the on-peak time period, determining whether a last process of the plurality of time-series processes should be performed in the on-peak time period; and - if it is determined that the last process of the plurality of time-series processes should be performed in the on-peak time period, operating the electric product in an energy-saving operation mode for reducing an energy-related value based on the recognized power information and the time information, wherein the operation of the electric product is changed so that only the last process or some processes including the last process are performed in the on-peak time period and the estimated power information is equal to or lower than the predetermined reference value.