Modeling of outdoor natural ventilation and energy performance for buildings in an industrial park

In tropical countries such as Singapore, roof temperatures can get very hot during the day. In order to cool the building to comfortable temperatures, fans and air conditioning are used and they take up considerable amount of electricity. One method of cooling without the use of any electricity is by using natural convection. When the roof gets heated, air below the roof would heat up and become less dense. The hotter air would then be more buoyant than the surrounding air thus gaining velocity and rise upwards. By having a double skin roof, the top roof would be heated causing air between both roofs to flow thereby causing convection. This helps reduce the temperature of the lower roof significantly as compare to a single roof. The objective of this report is to optimize the air gap height between the two roofs such that it would provide the most cooling. This study consists of both experiments as well as simulations. First experiments are conducted in order to investigate several factors. Some of these factors are angle, air gap height, effects of radiant barriers and thermal resistances. After which simulations are done and validated against experiment results to further evaluate the optimal height. From the experiment, it is found that at 10cm air gap height, it is the most optimal. From the simulation however, it is found that when the most optimal air gap height is 4.3cm. A reason for the differences in result might be caused by the different surroundings. In the simulation it is taken that there is no interference in the surrounding, however during the experiment, there are a lot of human traffic around the room. Moreover the room is air conditioned and with people walking in and out constantly, it can cause unpredictable winds. This can affect experiment results. In conclusion since the simulation results fit closer to the Azevedo and Sparrow [1] correlation, it is taken that the simulation results are more accurate and therefore 4.3cm is considered the most optimal. The reason being the thermal boundary layer thickness calculated across the heater is 4.3cm and any further increase in height would not have any increase in convection.Bachelor of Engineering (Mechanical Engineering