Energy and exergy evaluation of a multiple-PCM thermal storage unit for free cooling applications

• The performance is investigated of LHTS free cooling system employing multiple PCMs.
• The phase change process is predicted using the effective heat capacity method.
• The effects of inlet air temperature and air flow rate on the exergy efficiency.
• An optimization is performed based on the energy and exergy efficiencies.

Latent heat thermal storage (LHTS) is a technology that can help to reduce energy consumption for cooling applications, where the cold is stored in phase change materials (PCMs). Free cooling is a concept developed for air conditioning applications, in which coolness is collected from ambient air during night and released into the room during the hottest hours of the day. In this work, energy and exergy analyses are performed for a free cooling system using a LHTS unit employing multiple PCMs. The effects of inlet air temperature and air flow rate on the performance of the system are investigated. It is observed that the increase in exergy efficiency due to reducing inlet air temperature is more significant than effect from increasing the air flow rate during the charging process.