In this paper, a phase change material (PCM) to air rectangular heat exchanger is studied for an objective of electricity peak shaving. First, a set of dimensionless numbers are derived from physical equations to understand the storage device behaviour: 1/BiFo, Bi/St and Ste. Second, these numbers are used to select the PCM based on the thermophysical properties of the material. Finally, the storage device is pre-designed by a proper analysis of the remaining dimensionless numbers. With the methodology developed in this paper, it is possible to efficiently design solutions from the specification requirements of the storage system. (C) 2015 Elsevier B.V. All rights reserved.