Indoor climate has a three-dimensional spatial distribution caused by three-dimensional airflow. To understand building performance, we must integrate the spatial distributions into building simulations. This paper presents the development of a new method to extract heat transport phenomena in rooms from a few cases of computational fluid dynamics (CFD) analyses and how to integrate the data into a thermal simulation. We calculated the indoor environment, including the spatial distribution of temperature, with a very efficient algorithm with precision comparable to more complicated CFD simulations. As a first step, the method was applied to the problem of optimizing the proportional and integral gains in the proportional-integral (PI) control of air conditioning. As a result, after the few CFD analyses, we examined 800 cases to validate the PI control variables, and we found the optimum variable with very light computational load.