Thermal Coefficient Of Green Roof Essays

Thermal Coefficient Of Green Roof Essays

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(Hf) is considered as the convective heat exchange between the foliage and the nearby air which is sensible heat flux, and (Lf) is considered as the heat exchange due to evaporation at the foliage level. The energy balance equation at the soil level is presented in equation 3:
Based on previous equations and figure 6, properties of soil and vegetation layers influence on the thermal behavior of different green roofs.
Having the equivalent outside temperatures (Θe,eq) and the heat flux (ɸ), and equivalent periodic thermal transmittance of a green roof can be calculated through equation below:
Taking into account of thermal inertia of green roof components, density and specific heat of the soil and outdoor temperature have more impact on thermal behavior of green roof. According to previous researches about thermal behavior of green roof, the main parameters of components which significantly affect Yie value are LAI value and soil thickness. In little or no insulated roof, the effectiveness of these parameters become more than insulated roof [9, 17, 18].
Design parameters for software implementation to calculate heat flux of green roofs are presented below:
• Height of plants: Height of plants are limited to the values of 0.01m <5.0.
• Leaf reflectivity: Leaf reflectivity is the ratio of incident solar radiations that are reflected. It ranges from 0 to 1.
• Leas emissivity: Leas emissivity is the ratio of thermal radiations that are emitted from leaf surface compared to black body at the same temperature. It ranges from 0 to 1.
• Stomatal resistance: Stomatal resistance is the resistance of plant to transport moisture in unit of s/m. It normally ranges from 50.0 to 300.0 s/m.
• Roughness: It is related to the roughness of a partic...


... middle of paper ...


... and buildings.
Average low and high temperature, extreme hot and cold conditions, irradiance level, wind, and the amount of precipitation are factors which should be considered in selecting green roof types in a specific area. Green roofs have an effective impact in thermal performance of rooftop in different climate, however the amount of effectiveness depends on the climate and the type vegetated roofs [21, 22].
In cold climate or winter time, the extra insulation layer offers by green roof causes that the growing medium has higher temperature than surrounding atmosphere. This fact helps to reduce the heating demand of building. Increasing the substrate depth of green roof adds more insulation value and thermal mass and reduces the heating energy demand. Extra insulation also provides the cooling demand reduction during the summer time. Thus, in heating dominated

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