This paper presents a mathematical model for simulating the heat transfer process in a latent heat thermal energy storage tank containing spherical capsules that can be used in conventional air-conditioning systems. The thermal performance, including the melting point and melting latent heat, of a new phase change material (PCM), which is developed for use in conventional air-conditioning systems, is studied. The buoyancy of the encapsulated PCM during the melting process was specifically considered. The numerical method studied was an effective heat capacity method. An experimental cool storage air-conditioning system with a storage tank was designed and constructed. The model was validated by comparing the numerical results with experimental measurements. The effects of heat transfer fluid (HTF) inlet temperature, Stefan number, flow rate of heat transfer fluid, the complete discharging time, cold storage capacity of the storage tank and distribution of water temperature in the cold storage device were investigated. The results of the study indicate that although an increased flow rate does not appreciably change the total storage capacity, changing the inlet temperature does have an effect on total storage capacity. (C) 2013 Elsevier Ltd. All rights reserved.