Study on optimal layout and design parameters of ventilated roof for improving building roof thermal performances.

• Ventilated roof thermal performance is analyzed by multi-field coupling COMSOL method. • An optimal air velocity exists in air cavity to obtain a better roof thermal performance. • Roof thermal performance with air vents is better than that without air vents. • Thermal performance of ventilated roof can be enhanced by air deflectors and solar panels. • Optimal layout and design parameters are presented for the ventilated roofs. Building roofs play a pivotal role in energy conservation and carbon reduction of buildings due to their high peak heat gain and large roof area. However, the optimal layout and design parameters for ventilated roofs is not very clear. In this study, the influences of air vents, air inlet and outlet sizes, air velocity in the air cavity, solar panels, and air deflectors on the thermal performance of ventilated roofs were numerically investigated using a new thermal-flow-solar radiation coupling simulation approach and an experimentally validated COMSOL model. The research results show that a ventilated roof structure with air vents has a better thermal performance than that without air vents. The air velocity range of the air inlet between 1 m/s and 1.5 m/s shows a better energy-saving effect than the other air inlet velocities. The thermal performance of the ventilated roof first increases and then reduces as the air inlet and air outlet size increases. An optimal air velocity exists in the air cavity to obtain a better roof thermal performance. A ventilated roof structure with an air deflector exhibits better thermal performance than that without an air deflector. The larger the percentage of solar panel area to the roof area, the greater the energy savings of the ventilated roof. Thermal performance of ventilated roofs can be enhanced by using air deflectors and solar panels. The findings of this study can provide valuable suggestions for optimizing the design and assessing the energy saving-effects of ventilated roofs. [ABSTRACT FROM AUTHOR]