OICC Press International Journal of Energy and Environmental Engineering 2251-6832 13 2 (June 2022) 2022 02 06 The study of the impact of the phase change materials on the temperature changes of a library in Tehran, Tabriz and Yazd 10.1007/s40095-022-00477-6 EN Shiva Mehrani Department of Mechanical Engineering, South Tehran Branch, Islamic Azad University, Tehran, IR Pedram Pakravan Department of Mechanical Engineering, South Tehran Branch, Islamic Azad University, Tehran, IR Farivar Fazelpour Department of Energy Systems Engineering, South Tehran Branch, Islamic Azad University, Tehran, IR Journal Article 2022 02 06 Abstract In this research, the impact of phase change materials and its effectiveness towards the thermal comfort of a building wall was studied in a selected library in three cities of Tehran, Yazd and Tabriz with different climatic conditions. The DesignBuilder software was utilized to investigate the building thermal conductivity. All simulations were performed in two ways. In the first mode, it was presumed that there was no phase change material, and in the second one, a phase change material was used. The results indicated that by using phase change materials, thermal energy consumption decreases from 0.273 to 0.016 kWh for the library in Tehran climatic conditions. In Yazd city, the use of phase change materials decreases thermal energy consumption from 0.185 to 0.138 kWh. In Tabriz, which has a steppe climate with cold winters and pleasant summers, the use of phase change materials decreases energy consumption of the investigated room from 0244 to 0.209 kWh. The use of phase change materials in Tehran also reduces the average room temperature from 20.77 to 17.04 °C which resulted in a more favorable thermal comfort condition. The room temperature for the city of Tabriz without using phase change materials was 17.09 °C and in the case of using phase change materials, the average room temperature changed to 20.80 °C. In the city of Yazd, the temperature variations range from 17.2 to 21.2 °C.