A Comparative Experimental Study of Green Roofs Based on Radiation Budget and Surface Energy Balance

One of the major benefits of a green roof is its thermal performance compared to a conventional concrete roof building; it maintains indoor temperatures under varying outdoor temperatures. In this study, data were collected from four newly built detached buildings with a bare concrete roof, a highly reflective roof, and two green roofs, respectively. The results showed that the green roofs lowered the maximum indoor temperature by 6.83? on average compared to a bare concrete roof building, which potentially saves a substantial amount of energy required for cooling buildings. The surface energy balance analysis using the flux profile method showed that the difference in ground heat flux depending on roof type is crucial for determining the indoor temperature of a building. Moreover, the green roof consumed a considerable fraction of net radiation for the latent heat (70.7%), whereas the bare concrete roof used a larger fraction of net radiation for the sensible heat flux (45.3%) and ground heat flux (16.2%). the green roof consumed a considerable amount of net radiation for the latent heat flux, but little ground heat flux. By contrast, the bare concrete roof used a larger fraction of the net radiation for the ground heat flux and the sensible heat flux, which increased the temperature of both the indoor building and the air close to the surface. These results demonstrate that a green roof not only reduces indoor temperature fluctuation but also helps mitigate the heat island effect directly.