Thermal performance optimization of free cooling systems using enhanced latent heat thermal storage unit

Free cooling systems use phase change materials (PCMs) to store outdoor cold during the night and to supply it to the indoor environment during the day when the need for cooling increases. This work presents a numerical investigation of the performance enhancement of a free cooling system using a latent heat thermal storage (LHTS) unit employing multiple PCMs. The PCM storage system consists of several flat PCM slabs arranged in layers with a passage in between for the heat transfer fluid (HTF). Using the effective heat capacity method, the process of melting and solidification of the PCM is predicted. The energy storage effectiveness (as a new performance parameter for LHTS units) and coefficient of performance (COP) of the system are calculated. These two performance indicators are used to optimize the system. The suitability of both methods for optimization purpose is discussed indicating the superiority of the energy based (COP) method.