Abstract In the present work, the thermal management system (TMS) for cool energy storage has been designed and studied experimentally. A prototype test room was designed to investigate the performance study of the thermal management system (TMS) with different operation conditions to maintain the temperature in under comfort range. The room air temperature, ambient temperature and PCM temperature at different locations were measured continuously. The TMS has sixty PCMs based high density polyethylene panels. The experimental room temperature was maintained between 22 and 24 °C during the cool energy storage in TMS. The different heat loads were used to know the real performance of TMS system for maintaining the experimental room temperature. The results of the study showed that there is a significant variation in the time duration to exceed the thermal comfort temperature with different heat loads. The experimental room temperature was maintained at 9 h, 3:30 h and 2:30 h in the presence of thermal management system with different heat loads. In other words, the temperature profile of the test room with room heater of 1 kW is found to be longest when it is used in the presence of TMS, while it is found to be the shortest in the case of 3 kW room heater without TMS. Thus it can be concluded that the TMS can maintain the room air temperature for long time even with an active heating load and hence, the TMS used in this study is a good alternative for both passive and active building space conditioning applications.