A numerical study on a packed bed thermal storage unit with phase change material（PCM)having different melting points is presented.Paraffin is used as PCM and injected into polycarbonate spheres as phase change capsules.Hot water is used as heat transfer fluid（HTF)flowing from the top down to melt PCM and store latent heat.The capsules are placed in series in the tank based on melting points.PCM having higher melting temperature is placed closer with hot water inlet.One-dimensional Schumann’s model with steady-state flow field assumption is adopted to calculate HTF temperature

while the phase change of PCM is simulated using apparent heat capacity method.The energy and exergy performance in charging process of two arrangement modes containing two

three and four kinds different PCMs are investigated and compared with those of packed bed using only one kind of PCM.The energy comparison results indicate that the thermal storage unit with multiple PCMs has much higher charge rate and higher thermal efficiency than single PCM storage bed.In the exergy comparison

the storage bed with higher average melting point can store more exergy than that has lower average melting point.The utilization of multiple PCMs can dramatically reduce charge time

improving the storage performance.