Green Roof Thermal Conductivity

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Green roof thermal conductivity. A steady state heat transfer analysis was performed to assess the functioning and relative thermal performance of the green roof systems. Performance of growing media for green roofs a multi year laboratory testing campaign was carried out on 8 samples which aimed to define the thermal resistance reference values of growing media as a function of density and water content. A frequently cited benefit of green roofs is the thermal insulating effect of the growing medium but no u value calculation convention recognises it. Thermal conductivity varies between 0 046 0 179 w mk.

Commonly the layers of a green roof from the top down consist of surface vegetation substrate filter water retaining mat drainage root barrier and a waterproofing membrane that all sit atop the structural support. Many green roof soil parameters such as thermal conductivity specific heat capacity short wave reflectivity and albedo vary as a function of the moisture content. The best net heat flux gains for vegetated green roofs were 4 7 w m 2 for the sand roof and 7 8 w m 2 for the silt clay roof. The thermal conductivity for soil was only used on the acob roof analysis since the uppermost sensor used on the green roof analysis 2bn was sitting in 1 5 inches of soil above the surface of the ceiling.

Layer analysis at various intensities of frost penetration showed that the thermal conductivity of each layer decreased when penetrated by frost. Whereas in the case of buildings with. Moderate or no insulation a green roof acts as a thermal barrier. The thermal conductivity value for dry sand is 0 27 w mk ashrae 1967.

Traditional roof green roof n sensible et r q q q substrate 0 where r n net radiation q sensible sensible heat flux due to convection q et latent heat flux due to convection q substrate roof conductive heat flux through roof n sensible r q q roof 0 energy balance. Green roofs with silt clay soil required more than twice the amount of soil moisture than green roofs with sand to achieve similar roof heat transfer rates. Winter thermal benefits achieved from a green roof system depend on vegetation type and material properties of the layers including thickness physical structure and thermal conductivity.