A phase field model is for the first time employed to solve the phase change problem in a metal foam-embedded Latent Thermal Energy Storage (LTES) system. A phase field model deals with free boundary problems without tracing their positions, and therefore provides potentials of being extended to consider more complicated mechanisms: multi-dimension and volume change. The coupled heat transfer between PCMs and metal foams is solved based on the non-equilibrium heat transfer theory. Two phase fields are introduced to deal with phase change and volume change. Comparisons are made between the model predictions and the experimental data available in existing literatures. Two dimensionless groups of the material and structure parameters are identified to control the effectiveness of the system. An Effectiveness Map is also produced to distinguish the conditions under which incorporating metal foam into the PCMs is sensitive, lowly sensitive or irrelevant. The map provides a useful tool to guide the metal selection and structure design of the metal foams when enhancing the heat transfer of PCMs. Finally case studies are also carried out, in which the minimum thermal conductivity of copper/aluminium foams and the maximum k(int) can be determined by referring to the obtained Effectiveness Map. (C) 2013 Elsevier Ltd. All rights reserved.