Microencapsulated phase change material (MPCM) slurry, which has a superior thermal storage capacity compared with water, was introduced as a storage media in a thermal energy storage (TES) system for building cooling applications, but the key question was whether a competitive charging/discharging rate could be achieved.In this study, twokey indices, that is, the volumetric storage capacity and charging/discharging rate, were proposed to evaluate the performance of TES system in terms of practical feasibility.At a given charging/discharging temperature difference, the two indices respectively indicated the thermal storage density and the heat transfer behavior of a specific TES unit.A small-scale air conditioning system integrated with a coil in tank TES system was constructed to obtain reliable experimental data of the thermal storage and heat transfer behaviors of MPCM slurry and compared with the same system using water.In addition, as a widely used water storage system for its highly efficient charging rate, stratified water storage tank (SWST) was also compared with the novel coil in tank MPCM slurry cooling storage system.The experimental results exhibited that the novel MPCM slurry performs better than water in both of the indicators.Specifically, the volumetric thermal storage capacity of the MPCM slurry system is nearly twice that of water in the temperature range of 8 ℃ to 18 ℃, which provides a great utilization potential for the purpose of cooling load shifting and energy consumption saving.The charging/discharging rate of the coil in tank system using MPCM slurry is also higher than the same system using the sensible storage media, water.However, the response time of the system was not as short as expected.The charging/discharging rate was observed to be obviously slower than the SWST system.Therefore, the enhancement of heat transfer of the TES system using PCM warrants further investigation.The two indices presented in this paper provide a reliable criterion to evaluate the performance of different TES systems.For an industry application and design optimization of TES system, both of the two indices should be considered carefully.