In this study, to obtain basic information for the design of a latent heat storage system, (1) the cylindrical type and the rectangular type of latent heat storage elements were designed, (2) the finite element method was adopted for the prediction of temperature profile of phase change material in heating and cooling process, and (3) experiments were performed to verify the numerical solutions, and then (4) the optimum size of latent heat storage units was predicted by the computer simulation. The results could be summarized as follows : (1) In cooling process, the predicted temperatures of latent heat storage units by computer simulation were in good agreement with measured. (2) The effective diameter of cylindrical element was observed to be 28 mm and the effective thickness of rectangular element was observed to be 21 mm.