In this work, a thermal energy storage system was designed and equipped with measuring instruments to study heat transfer characteristics and energy storage and release. In this system, a cubic container which is made of plexiglass was filled with dodecanoic acid as a phase change material. In order to transfer heat to the storage container, a constant temperature heat exchanger was designed and mounted on the side of the container. Several experimental tests were conducted for both the melting process (energy charging) and solidification process (energy discharging) with setting the temperature at 60 and 70 degrees of Celsius for the former experiments and 15 and 10 degrees of Celsius for the latter ones. Result indicated that the maximum amount of stored energy was 209 kJ/kg in the charging process. Furthermore, the charging process time was reduced, at most, by 42% and the absorbed energy was increased 9% when the temperature of heat exchanger was increased 10°C. Also the discharging process time was decreased 9% as the temperature of heat exchanger reduced by 5°C.