Green Roof Essay

708 Words2 Pages

(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 …show more content…

• 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 particular material layer. The possible options for this character are “VeryRough”, “Rough”, “MediumRough”, “MediumSmooth”, “Smooth” and “VerySmooth”.
• Thickness: It is related to the depth of the growing media layer in meters.
• Conductivity: Thermal conductivity of the growing media which is related to the wet or dry environment (W/(m-K).
• Density: It is related to the density of the dry growing media …show more content…

Green roof can protect the roofing membrane against ultra-violet (UV) radiation and prevent physical damage due to degeneration of insulation and roofing materials. It can block solar radiations and decrease daily temperature fluctuations during summer and winter. All of these benefits make the roof lifetime longer [19].
The heat gain and heat loss through green roof are mainly defined by solar radiations coming from the sun. Green roof useful for reflecting solar radiations and reducing heat absorption by evapotranspiration. In addition, it can minimize the amount of heat transmitted through the roof membrane due to extra insulation. Determination of the green roof materials, foliage characteristic, and soil features which affect thermal performance of roof is necessary for designers [20].
1.2.3.2 Climate/Seasons consideration:
Solar radiation can change seasonally and in different locations, and can impact thermal performance of vegetated roofs and

Open Document