The integration of Phase Change Materials (PCMs) in buildings as a potential method to improve indoor thermal comfort can be achieved via free cooling/heating approach. This paper presents the results of a study on indoor thermal comfort and energy efficiency regarding the PCM's positive role when applied to the new constructive solutions, inside a building with a ceiling fan-assisted ventilation system. The scope was driven to investigate the potential of the solution for overheating/overcooling mitigation. The thermal performance of the proposed system was experimentally evaluated by comparing the behaviour of a prototype test room (including PCM panel), with the behaviour of a similar prototype test room, in which no PCM was added. First the experiments are conducted in an artificial climate inside a laboratory environment chamber which was controlled by harmonic and linearly rising/falling temperature changing processes. Experiments were performed based on 5 level RSM CCD method to quantify the potential effects of using PCM panels and to determine individual/interactive effect of parameters on thermal discomfort index, PPD. Results indicate that minimum discomfort level can be achieved when inlet air temperature and humidity, fan rotating speed and PCM slab height and thickness were set to 29, 48%, 115 rpm, 31 cm and 2.6 cm, respectively. PPD was obtained 4.1% in the optimized condition. Then optimised tests rooms were subjected to realistic daily temperature profiles during winter and summer. In summer case, the experiments proved that the PCM application in one of the rooms lead to an overheating reduction of 13.83% representing a PCM efficiency of 56%. Under the winter condition during two months, the experiments showed proposed hybrid system can averagely reduce discomfort level around 2.61% corresponding a PCM efficiency of about 35.49%. Based on the results, proposed system have the potential to shift cooling/heating energy demand away from peak hours. (C) 2019 Elsevier B.V. All rights reserved.