ประสิทธิผลของการออกแบบการระบายอากาศช่องใต้หลังคาเพื่อป้องกันการถ่ายเทความร้อนจากหลังคา / วิกรม จำนงค์จิตต์ = The effectiveness of attic ventilation design to prevent heat transfer from roof / Wikrom Jumnongjit
This study is experimental research, carried out on location, with the aim to study the effectiveness of attic ventilation design in preventing heat transfer from the roof of a house in a tropical climate. The building used in this experiment was a one-storey house, 4 metres in width, 4 metres in length and 2.4 metres in height, with a roof covered with concrete tiles. The angles of the roof were about 40-45 degrees. In the experiment, ventilating fans were used to simulate natural ventilation. To gather the data for this experiment, scientific equipment was used to record and collect information every hour for three consecutive days, or 72 hours per single experiment. To analyze the data, the degree each hour above 18 ํC was utilized to compare the results of the experiment. This research is divided into there parts. The first part studies the effectiveness of attic ventilation in preventing heat transfer from the roof. It was found that attic ventilation was not able to reduce heat transfer effectively, as it could lower the average room temperature by only about 0.1-0.2 ํC. The second part deals with improvement of the design to reduce heat caused by heat transfer from the roof. It was discovered that the use of fiber asbestos sheets, about two inches thick, spread over the ceiling, the use of one-sided aluminium foil under the purlin, and the use of two-inch-thick asbestos sheets together with one-sided aluminium foil to spread under the purlin, were more effective to prevent heat transfer from the roof than attic ventilation. The third part is concerned with the economy of design and heat reduction improvement. The study revealed that investment on attic ventilation to prevent heat transfer was not worth the expense when compared with the use of two-inch-thick fiber asbestos sheets to prevent heat conduction and the use of aluminium foil sheets to prevent heat radiation. The cost of roof improvement by means of attic ventilation was about 162.5 baht per square metre while the average room temperature and the temperature at the surface of the ceiling could be reduced by about 0.1 ํC. Investment in the use of two-inch-thick fiber asbestos sheets was about 81.5 baht per square metre and the average room temperature could be reduced by about 0.4 ํC and the average temperature at the surface of the ceiling by 0.3 ํC. As for the investment on one-sided aluminium foil sheets, the cost was about 108.5 baht per square metre and the average room temperature and the temperature at the surface of the ceiling could be lowered by 0.3 and 0.2 ํC respectively. The results of this study indicated that, with the increase in attic ventilation, the reduction of heat transfer only slightly improved. Therefore, other alternatives should be considered in the improvement of roof design to reduce heat transfer. For example, the use of fiber asbestos sheets is a more effective technique and the cost is not widely different. In addition, the research findings revealed another interesting phenomenon. During the night, the average temperature of a room with asbestos sheets in the roof was higher than a room with or without attic ventilation, and it was higher than a room that used heat radiation prevention systems in the roof as well.
