This paper presents the results of a thermal performance analysis of a phase change thermal storage unit. The unit consists of several parallel flat slabs of phase change material (PCM) with a liquid heat transfer fluid (HTF) flowing along the passages between the slabs. A validated numerical model developed previously to solve the phase change problem in flat slabs was used. An insight is gained into the melting process by examining the temperatures of the HTF nodes, wall nodes and PCM nodes and the heat transfer rates at four phases during melting. The duration of the melting process is defined based on the level of melting completion. The effects of several parameters on the HTF outlet temperature, heat transfer rate and melting time are evaluated through a parametric study to evaluate the effects of the HTF mass flow rate, HTF inlet temperature, gap between slabs, slab dimensions, PCM initial temperature and thermal conductivity of the container on the thermal performance. The results are used to design a phase change thermal storage unit for a refrigerated truck. (C) 2011 Elsevier Ltd. All rights reserved.