Study on the Optimum Roof Type with 30° Roof Angle to Enhance Natural Ventilation and Air Circulation of a Passive Design

One of the major problems in modern housing design is overheating. Occupants suffer higher indoor temperatures due to a lack of natural ventilation. This issue arises because of poor passive design. A good passive design promotes natural ventilation and provides better indoor air temperatures without reliance on mechanical cooling systems. The roofing system plays an important role in a house’s design. Since the roof contributes to 70% of the total heat gain, it is important to investigate its design to reduce the impact of overheating. It has been found that many roofs lack a ventilation system in the top part of the house. These openings in the roof provide areas for trapped hot air to exit into the environment. The openings also enhance natural ventilation and allow for effective air circulation inside the house. The optimum roof is designed to tackle this matter by reducing the overheating inside the house, especially during the hottest hours of the day. The hot air exits based on the differences in air density and due to prevailing wind. In this study, the optimum roof was tested on a small-scale model and verified by simulation using computational fluid dynamic (CFD) software, namely ANSYS 18.0. From the data obtained, it was proven that the opening in the roof reduced the indoor temperature. In conclusion, the optimum roof could improve the passive design and help to reduce overheating inside a house.

Computational fluid dynamic simulation; Heat transfer; Optimum roof; Ventilated roof

Malaysia is located in the equatorial region and experiences high temperatures with high relative humidity throughout the year. The average solar radiation in this hot, humid climate is between 4.21 kWh/m² and 5.56 kWh/m², annually (Azhari et al., 2008). Malaysia receives 8.7 hours of sunlight per day (Malaysia Meteorological Department, 2014). The recommended thermal comfort level ranges from 25 to 28°C (Ibrahim, 2004). Based on a previous study on concrete terrace houses in Malaysia, indoor temperatures are only comfortable to the occupants for a few hours every day (Ibrahim et al., 2014a). The same study also discovered that the indoor temperature could reach more than 30°C during the daytime. Increased indoor temperatures in a building are due to poor passive design. Designers should adapt more natural ventilation as part of the passive design, especially at the top part of the house. The reason for focusing on the top part of the house is because hot air rises from the bottom part of the house to the upper part due to density differences. The differences between the outdoor air pressure and the indoor environment creates suction. Hence, the hot air naturally passes from inside the house to outside without depending on a mechanical ventilation system.

Poor passive design could lead to overheating. In addition, the occupants in modern low-cost housing suffer overheating due to poor ventilation and roof design problems (Ibrahim, 2004). One research study found that the recorded indoor temperature of a modern low-cost house was higher than recommended for the occupants’ level of comfort (Tinker et al., 2004). Due to this, occupants rely on mechanical means to cool their houses, which incur energy consumption costs to power the electrical components. A previous study concluded that openings in the roof’s surface could help to reduce the indoor air temperature (Ibrahim et al., 2014a). This study focuses on roofing because it plays an important role in controlling the amount of heat transmitted from the roof surface into the internal area.

This study concluded that the openings on the roof surface provided additional ventilation for the house. The optimum roof works best when the condition of the house is fully closed and fully opened condition. The optimum roof showed its significant reduction of indoor temperature under fully closed condition. This concluded that the openings on the roof surface played an important role in reducing the temperature inside the house. The optimum roof helped to reduce the indoor air temperature by up to 10°C compared to the normal roof.

The authors would like expressed appreciation to Universiti Malaysia Sarawak (UNIMAS) for providing staff, a laboratory, and other facilities to assist with this research.

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