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THE HEAT LOAD THROUGH THE ROOF OR ENERGY DEMAND FOR COOLING OF THE ROOM UNDER THE ROOF - WHICH APPROACH TO THE EVALUATION OF ENERGY EFFICIENCY OF GREEN ROOF IN SUMMER TO CHOOSE
Abstract
The extensive or intensive green roofs are today the common solution for roofs at new and retrofitted buildings in different climatic regions. In terms of region where the building is located the thermal insulation in the roof is or not. In the direction from the equator further the thermal insulation in the roof is important to decrease the heat flow from the building to the exterior during winter months. The presence of thermal insulation on the roof also influences the heat load of rooms under the roof during summer months. What is the impact of green roofs on the cooling of rooms under the roof. The analysis in this article is comparing two different approaches to evaluate the energy efficiency of green extensive roof in the climatic conditions of Slovakia. The comparison is based on the results from the computer simulation of the multi-dwelling house in the software DesignBUILDER v7. On one side the decrease of solar heat through the green roof is analyzed in comparison with roof without substrate layer. On the other side the decrease of energy demand for cooling for the room under the green roof is analyzed in comparison with roof without substrate layer. The results for the evaluation of energy efficiency of green roofs are very different. The decrease in energy demand for cooling rooms under the green extensive roof is under 5 %. The decrease of the solar heat through the green extensive roof is in the range 22 - 33 % depending on the roof construction, if it is lightweight or heavyweight roof structure. The energy demand for cooling of room considers all impacts such as solar heat gains through the glass of windows or opaque constructions but also internal heat gains. We can say that it is a complex evaluation of the impact of green roofs on the building. The assessment of the impact of green extensive roofs that is based on the decrease of heat load through the roof is a very isolated approach and so, it is not proper for the evaluation of the energy efficiency of green extensive roof during summer.
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References4
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