Enhancement in free cooling potential through PCM based storage system integrated with direct evaporative cooling (DEC) unit

The present work reports the enhancement in free cooling potential using a modified cooling system compared to the conventional free cooling system. The proposed modified system is a novel pilot scale model packed with spherically encapsulated phase change material in a cylindrical tank along with water spray nozzles (direct evaporative cooling unit) at the inlet of the tank. The experiments were conducted in Bangalore, a city located in south India that possesses moderate/temperate climate throughout the year. Considering the local ambient conditions, an organic phase change material with the phase transition temperature range of 25.6-27.1 °C was used in the present study. Significant reduction in total charging duration and enhancement in heat transfer rate was achieved through the hybrid cooling system. The reduction in charging duration of 28.7% and 34.8% was observed for the proposed hybrid cooling system at heat transfer fluid (HTF) inlet velocities of 2 and 1.5 m/s respectively. It is observed from the results that in the experiments conducted with conventional free cooling system at 1 m/s HTF velocity, the phase change material (PCM) placed in the last two rows of the storage tank did not reach its end freezing temperature even after 10 h of experimentation due to the low heat transfer rate, whereas in the experiments conducted with the modified free cooling system, the storage tank is completely charged at all HTF velocities. It is construed from the results that the integration of evaporative cooling unit along with phase change material based free cooling system aids the chosen phase change material to completely solidify at a faster rate and augments the thermal performance of the storage unit. The proposed system can be operated as a single stand-alone cooling system to meet the cooling demand of the buildings or it can be integrated with the mechanically operated HVAC systems to achieve energy efficiency in the overall cooling system.