Disclosed herein are an air conditioner system and a controlling method thereof. In a situation that air-conditioning systems such as air conditioners and refrigerators are installed and operated in a site, real-time operation data are acquired and the air conditioning and efficiency are calculated at the site. By comparing performance data provided by a device manufacturer and the real-time operation data, device performance is corrected for the site's installation environment. By using corrected device performance, it is possible to save building facility energy by providing optimal operation number control suitable for the installation environment.