This study was conducted to characterise thermal environmental acceptability for various air-conditioning systems. The authors developed a new thermal comfort index called a P-R chart using the concepts of "provided temperature" and "required temperature" for use in evaluating uniform, high-quality indoor thermal environments and non-uniform, unsteady thermal environments. In this study, first, the authors surveyed the required temperature distribution of workers. Then they surveyed indoor thermal environmental stabilities in the four offices during the summer with different air-conditioning systems to calculate provided temperature distribution. Finally, the indoor thermal acceptability in offices was evaluated using the P-R chart. The results showed that the convective air-conditioning systems caused wide temporal and spatial variations in the thermal environment. Therefore, in buildings with convective air-conditioning systems, even if the planar average thermal environment is categorised as comfortable, it is presumed that workers sensitive to cold or heat will complain of discomfort more frequently than those in buildings with radiant air-conditioning systems and floor-supply displacement HVAC systems, because the probability of workers sitting in cold- or hot-spot areas is higher in the former case.