Improvement of thermal performance of double skin roof with forced ventilation

• Main Author: Gao, Wen
• Other Authors: Li Hua
• Format: Final Year Project
• Language: English
• Published: 2014
• Subjects: DRNTU::Engineering
• Online Access: http://hdl.handle.net/10356/55255
• Institution: Nanyang Technological University

Reduction of electric consumption helps to slow down the effect of green-house and provides a better living environment for the next generation. In Singapore the cooling system takes up the majority of the electricity consumption. There is an increasing trend of using mechanical ventilation system to secure thermal comfort. Double-skin roof greatly reduces the heat transfers of both conduction and convection from the roof to the ceiling of the building. Previous works mainly focused on optimal air gap and the inclined angle for the better thermal performance of the double-skin roof. Roof ventilation is one of effective ways to improve the building energy efficiency. The objective of this report is thus to improve the double-skin roof thermal performance through forced ventilation in the tropical environment, such as Singapore. This project is carried out via both laboratory experiment and CFD simulation (FLUENT) to analyze the thermal performance of double-skin roofs, which are characterized by the different wind velocities based on Singapore climate. An experimental setup is carried out to study the heat ventilation percentage and airflow rate in the forced ventilation, compared to nature ventilation. The experiment is done by varying different factors like the inclination from 0° to 30°, air gap of 3 mm and 6 mm and wind velocities from 0.5 m/s to 4 m/s. A Computational Fluid Dynamic (CFD) model is developed to simulating the. The results of the study show that the thermal performance of double-skin roof can be improved significantly as the wind velocity increases for the forced ventilation. Simulation result indicates that a velocity of 4 m/s gives the best thermal performance for the double skin roof at air gap of 30 mm and inclined angle of 15°. The small changes in the air gap and inclined angle have an insignificant impact on the thermal performance of forced ventilation. As the average wind velocity in Singapore is ranges from 3m/s to 5 m/s, such that the forced ventilation is the most effective way to improve thermal performance of double skin roof, with the air gap of 30 mm, the inclined angle of 15° and the length to the air gap ratio equal to 50 in Singapore.