University of Twente Student Theses


The energy conservation provided by green roofs on metal sheets in a tropical climate

Meijer, J. (2009) The energy conservation provided by green roofs on metal sheets in a tropical climate.

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Abstract:Green roofs are an ancient building technique and were already constructed in the days of Mesopotamia. In the last few decades they have made a re-appearance in the building sector. Green roofs have an ecological character and are especially useful in urban areas where they can oppose the effects of the current urbanization problems. Most of the current worldwide green roof performance research is based on a more or less specific design for concrete slabs in moderate climates. This research distincts itself in two ways; the research is performed in a tropical climate, and their performance was studied on metal sheet roofs, the most commonly used roofing material in the area of San Pedro Sula, Honduras. The climate has a substantial influence on the circumstances the research is in. Also, the climates influence on the building techniques used in Honduras is substantial. Insulation is far less important than in a moderate climate. Instead of preventing heat entering by insulation, natural ventilation techniques are often used to let excess heat flow out of a building. Another difference due to the climate is the plant selection. The tropical climate asks for another type of vegetation, than the most used type; sedums. The search for the ideal plant is not yet completed, criteria include; growth control, heat-, drought, - and rain resistance. The use of corrugated iron sheets influences the characteristics of the roof. Compared to concrete slabs, corrugated iron sheets have a lower, almost negligible R-value. This results in fast transportation of incoming as well as outgoing heat. A corrugated iron sheet is a better radiant barrier, which means it reflects a higher rate of incoming (solar) radiation than concrete. The advantages of green roofs are undoubtedly numerous from the ecological part of view and are especially suitable for areas with a high building density. In these areas more and more natural surfaces are covered by building materials such as concrete, metal and asphalt. This transduction of used materials influences the environment. Problems with impervious surfaces include higher ambient air temperatures. Green roofs are one potential remedy for this problem. Green roofs act positively on the inner climate of a building and prevent heat radiation to the surrounding area as well. The green roofs cool a building by providing shadow over the roof, a main factor in passive cooling. The plants use a substantial part of the solar radiation for their biological functions, in so doing working as a radiant barrier. Furthermore they increase the insulation value and heat capacity of a roof. All these factors reduce the heat gain of a building and can save energy consumption for air conditioning, which affects the ambient air temperatures. Establishing plant material on rooftops provides a multifunctional solution for the urban problems of the 21st century. Environmentally speaking there are no known disadvantages. Next to energy conservation and lowering ambient air temperatures benefits include storm water management, mitigation of the urban heat island effect, increased longevity of roofing membranes, and mitigation of noise and air pollution, as well as a more aesthetically pleasing environment in which to work and live.
Item Type:Essay (Bachelor)
Faculty:ET: Engineering Technology
Subject:56 civil engineering
Programme:Civil Engineering BSc (56952)
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