Reducing a building's energy consumption and providing better indoor environmental quality (IEQ) are the two major issues that building professionals are facing all over the world. It is not easy, however, to simultaneously address both issues. Therefore, this study aimed to establish the optimal occupant behavior that can simultaneously reduce total energy consumption and improve the IEQ, using an energy simulation and optimization tool. This study also developed an integrated IEQ score by combining three different IEQ indices (i.e., thermal comfort, indoor air quality (IAQ), and visual comfort) for building users to easily understand the IEQ condition. To analyze the effects of occupant behavior by region, the education facility was selected as the target facility, and five target regions were selected considering the Koppen climate classification system and the C40 Cities Climate Leadership Group. Finally, a total of 5 x 1.01 x 10(22) occupant behavior combinations can be generated in the five target regions. As a result, among the four target variables (i.e., total energy consumption, thermal comfort, IAQ and visual comfort), the total energy consumption of the optimal solution was found to have changed most dramatically compared to that of the basic condition in terms of percentage (94.7%), due to its strong correlation with the overall occupant behavior (the highest correlation coefficient: 0.879). Therefore, it is shown that occupant behavior has more influence on the total energy consumption than on the three IEQ indices. Among the three IEQ indices, the IAQ of the optimal solution decreased most significantly compared to that of the basic condition (the highest reduction ratio: 4.04% in Ulsan), which indicates that the IAQ has more influences on the integrated IEQ score than thermal and visual comfort. The facility manager and the building user can operate the building for reducing total energy consumption and improving the IEQ considering occupant behavior, which can be used as the building management guideline in various regions. (C) 2017 Elsevier Ltd. All rights reserved.