Feasibility study on the year-round operation of PCM based free cooling systems in tropical climatic conditions

The free cooling system (FCS) is a conventional system in which the cool energy available in the night ambient air is stored in the phase change material (PCM) and retrieved later during the daytime to reduce the temperature variations in a building. The thermal performance of such passive cooling system predominantly depends on the local climatic conditions. Especially, in tropical countries, where the nighttime ambient temperature for most of the months in a year is high, the complete solidification of PCM through free cooling concept is a challenge. In recent years, several enhancement techniques were introduced to augment the performance of FCS. One such technique is the enhanced free cooling system (EFCS). The EFCS is a hybrid system where the FCS is coupled with a direct evaporative cooling unit to augment the thermal performance of FCS during the PCM solidification process. However, the year-round operational feasibility and the applicability of these cooling systems in tropical climatic conditions are yet to be explored. Considering the above, an assessment study was carried out in the present work with the aim of estimating the monthly average cooling potential of FCS and EFCS under different climatic conditions of a tropical country. The results indicate that cities with temperate and cold climates possess operational feasibility for the FCS throughout the year, whereas for composite/mixed, hot-dry, warm-humid climates, the operational feasibility of the FCS during summer is low and not recommended. On the other hand, results showed that the integration of the evaporative cooling unit with FCS increases the cooling potential and feasibility of year-round operation of the system in all the climate. In addition to the assessment study, the experimental results obtained using FCS and EFCS under real-time ambient conditions of hot-dry, warm-humid and temperate climates are presented. The main aim of the experiments is to study the solidification behavior of the PCM in the above-said climates during the summer and to verify the results of the assessment study. •Free cooling potential assessment of PCM based storage systems for 57 cities in India are carried out.•Experiment results were used to verify the results of cooling potential assessment study.•During summer, the operation of FCS is not recommended in hot-dry, composite and warm-humid climates.•However, by means of EFCS, the application of free cooling in buildings even in summer is possible in