The building sector is the largest final end-use consumer of energy in the European Union. Substantially heat losses occur through windows and translucent areas, therefore it is crucial to mitigate the energy transfer between these boundaries. The use of phase change materials (PCMs) is presently a good solution to improve the energy performance of building components, namely the glazing or window shutter protections. It is presented and discussed an experimental campaign of a full scale outdoor test cell that is composed by two side-by-side compartments. The internal compartments were submitted to similar weather conditions in a Mediterranean climate during the winter season. The south oriented facade is a glazed area that incorporates a window protection system-window shutter. It was tested and compared two similar windows shutters, one containing PCMs and the other without PCMs (referred to as reference compartment). During the experimental period the external air temperature fluctuated froth 4.5 degrees C to 14 degrees C, which represent maximum thermal amplitude of 9.5 degrees C and the relative humidity ranged between 75% and 95%. The daily average solar radiation ranged from 25 W m(-2) to 110 W m(-2) and the maximum value reached was 310 W m(-2). The maximum indoor air temperature measured of the compartment with the PCM shutter was 37.2 degrees C, which is 16.6 degrees C lower than the indoor air temperatures in the reference compartment that reached 53.8 degrees C. The minimum indoor air temperature for both compartments is similar, however the minimum air temperature of the reference compartment drops faster. The maximum heat flux on the internal wall surface of the compartment with the PCM shutter was 6.5 W m(-2) and the minimum -3 W m(-2) against 16 W m(-2) and -8 W m(-2) of the reference compartment. The results reveal the PCM potential for the thermal regulation of indoor spaces as well as improving the energy efficiency of building spaces. (C) 2014 Elsevier B.V. All rights reserved.