Surface heat budget on green roof and high reflection roof for mitigation of urban heat island

In this study, the surface temperature, net radiation, water content ratio, etc., of green roofs and high reflection roofs are observed.  The heat and water budget are compared to each other. In the daytime, the temperature of the cement concrete surface, the surface with highly reflective gray paint, bare soil surface, green surface and the surface with highly reflective white paint are observed to be in descending order.  On a surface with highly reflective white paint, the sensible heat flux is small because of the low net radiation due to high solar reflectance.  On the green surface, the sensible heat flux is small because of the large latent heat flux by evaporation, although the net radiation is large.  On the cement concrete surface and the surface with a highly reflective gray paint, the sensible heat fluxes have almost the same values because their solar reflectance is approximately equal.  These tendencies of the sensible heat flux accord with the pitch relation of the surface temperature.  Methods to estimate the quantity of evaporation, evaporative efficiency, heat conductivity, and thermal capacity are explained, and the observation data is applied to these methods.

Source: Building and Environment

Publication Date: August 2007

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