This paper describes how to design a PCM-air heat exchanger once an application is specified. Free-cooling and temperature maintenance in rooms with special requirements possess high potential for PCM application in different countries according to their climate. Until now, the low thermal conductivity of PCM and air hindered the development of suitable heat exchangers. The overall objective here is to apply methodologies to study PCM-air heat exchangers that allow the development of applications with technical and economical viability. In particular, using the combined technique of design of experiments and numerical simulations, the feasibility of the possible application of this type of equipment is studied and optimized for temperature maintenance in rooms. (C) 2012 The Authors. Published by Elsevier Ltd.