| Summary: | 碩士 === 國立嘉義大學 === 園藝學系研究所 === 97 === As cities develop, the ratio of impermeable surfaces to green areas increases in urban areas. These impermeable surfaces with small specific heat and human activities will result in high ambient air temperature, which cause ‘heat island effect.’ Applying the green roof on flat roofs may mitigate the urban heat island effect. It not only increases the percentage of greenery coverage but also reduces the area of impermeable hard surfaces. In addition, applying the net shading over green roof area may control the sunlight and radiation intensity. Moreover, it will enhance the thermal comfort and extend the time of using roof garden.
In this study, we made use the method of literature review to understand the heat transfer of a building and carried out two field experiments to investigate the thermal environment of the roof top. One is to apply the net shading and the other is artificial light-weight soil greening respectively. The results reveal that applying net shading on bare roofs reduces the peak ambient air temperature, wet bulb globe temperature (WBGT), and mean radiant temperature (MRT) by 1.22℃, 3.82℃, and 15.18℃ respectively. The influence of greening under net shading to thermal environment is limited. As regards to the influence on outdoor thermal environment, net shading is able to extend the time that is adequate for outdoor activities. Regarding WBGT 30.6℃ as a standard of adequate temperature for outdoor activities, there is 72.73% of time period not adequate for continuing outdoor activities on bare roof while all the time period falls within the standard under net shading during 8:00-18:00. There were similar results while regarding MRT 21~47℃ as a standard of adequate temperature for outdoor activities. Applying artificial light-weight soil greening on bare roof does not influence the thermal environment a lot in winter. The greening reduces the peak WBGT and MRT by 0.32℃ and 1.06℃ respectively at the height of 150 cm above the surface, while the peak WBGT and MRT will be reduce by 0.35℃ and 1.8℃ respectively at the height of 100 cm above the surface. The MRT drops more when applying greening which is considered more beneficial. Applying turf greening on roof surface immensely influences the thermal environment of the roof top surface and indoor underneath. Comparing to the bare roof, turf greening reduces the peak upper surface temperature by 25.3℃ while the peak lower surface temperature will be reduced by 7.15℃, and the heat flux will be reduced by 491.71 Wh/(m2•day). The estimated cooling load of the top floor from measured values reveals that the cooling load under green roof is 45.86Wh while it is 116.46Wh under bare roof. There is 70.60Wh difference between them.
|
|---|
