Radiation budget and surface energy balance of green roofs using flux profile method

One of the primary advantages offered by a green roof is its ability to regulate indoor temperatures more effectively in response to changing outdoor temperatures, in contrast to a traditional concrete roof on a building. This advantage aids in decreasing the amount of energy needed to cool the building during warm seasons and heat it in colder seasons. This investigation gathered data from four recently constructed detached buildings: one with a bare concrete roof, another with a highly reflective paint roof, and two with green roofs. The focus was on examining the complete radiation budget and surface energy balance of green roofs compared to other roof types during a summer season in Korea. The thorough data collected allowed for a quantitative assessment of how green roofs behave in terms of energy balance, particularly when compared to bare concrete roofs. The monitoring period for this study took place over a week, from July 21, 2021, to July 28, 2021. Results indicated that, on average, green roofs reduced the maximum indoor temperature by 6.83℃ compared to buildings with bare concrete roofs, potentially resulting in significant energy savings required for cooling. Additionally, the analysis of energy balance using the flux profile method highlighted the significance of the difference in ground heat flux in determining indoor building temperature. The findings also revealed that green roofs utilized a substantial portion of net radiation for latent heat flux (70.7%), but a minimal amount for ground heat flux (0.5%). Conversely, bare concrete roofs used a larger portion of net radiation for ground heat flux (16.2%) and sensible heat flux (45.3%), resulting in greater warming of both indoor building areas and the air near the surface. These outcomes illustrate that green roofs not only stabilize indoor temperature fluctuations but also directly assist in mitigating the heat island effect.