With the use of aquifer thermal energy storage for heating and cooling, one of the main aims of this study was to establish a method for keeping energy consumption levels low while heating or cooling utilizing a large quantity of stored water. Therefore we have proposed continuous cooling and heating requirements whereby the difference between the ambient air temperature and the water temperature is minimized. This paper reports the subjective ratings of the room thermal sensations by a large number of Japanese subjects while the thermal condition was monitored. Radiation, thermal convection and evaporation were analyzed using a cylindrical model to approximate the human body. The results indicated that thermal comfort was obtained under the following conditions : (1) the ratio of the radiation heat transfer coefficient to that of convection was 2.34 for cooling and 2.19 for heating, and (2) the ratio of heat loss by evaporation to the sum of radiation and convection was 0.052 for cooling and 0.050 for heating. Finally, a new thermal design process based on thermal comfort was proposed.