The COVID-19 pandemic forced many schools to switch to online classes. Although there has been a movement to return to face-to-face classes since then, many schools are still struggling to ensure safety during classes and subsequent examinations in a face-to-face environment. In this study, we attempted to visualize the relationship between class usage and building air conditioning management by installing CO2 sensors at fixed points in classrooms and also applied them to environmental monitoring during examinations to grasp the risks in real time and provide a response.