Improving energy efficiency of a ventilated tiled roof by using phase change materials

The adoption of ventilated roofs and facades, as well as the integration of phase change materials (PCMs) in the building envelope, have proved to be effective as passive cooling techniques in reducing solar heat gain through the building envelope during the summer period and, therefore, reducing the energy requirement for cooling. Even though much research has focused on each of these strategies individually, their combination has not been deeply studied yet. Preliminary numerical studies were carried out on the application of PCMs on a pitched ventilated tiled roof and the most effective position turned out to be suspension in the middle of the above sheathing ventilation (ASV) channel. Based on this conclusion and exploiting an existing mock-up facility, two equivalent pitched ventilated roofs with an air gap of 4cm were built to cover two identical rooms, each one equipped with a fan coil; one with a 0.007m PCM layer suspended in the middle of the ASV and the other one without. They were then tested under real conditions at the TekneHub Laboratory at the University of Ferrara. The PCM supplied was an inorganic PCM with a melting temperature of 25°C and the roofs had a steel structure upon which a wooden deck covered by a polyolefin membrane was installed, with a cladding layer of Portuguese tiles. The behaviour of the two configurations were compared in terms of temperature, heat flux, velocity of the air in the ASV, and energy requirement for cooling, which were monitored through T-type thermocouples, heat flow meter, anemometers and energy meters, respectively. The aim of the research was to validate the numerical results and confirm that the combination of the two strategies allows further improvement of roof performance. Results showed consistent differences between the two configurations corresponding with the melting range of the PCM, which brought variances in the temperature of the extrados of the wooden deck of more than 5K and a reduction of the HVAC system operating time in the room with the PCM roof.