Optimization of heat transfer coefficient in green roof modules based on life cycle carbon emissions

As cities face increasing challenges related to climate change and energy consumption, green roofs offer an innovative solution by improving building insulation, reducing energy demands, and mitigating urban heat island effects. However, the environmental benefits of green roofs, particularly regarding carbon emissions and heat transfer, are not well understood. This study aims to address this gap by investigating the influence of life cycle carbon emissions on the heat transfer coefficient in green roof modules. The study quantifies the roof heat transfer coefficient of green roof modules and their carbon emission benefits across their life cycle, with a focus on identifying optimization pathways for maximizing both energy efficiency and carbon reduction. Using IPCC guidelines, assimilation methods, and life cycle assessment (LCA) techniques, models for calculating heat transfer and carbon emissions at each stage of the life cycle are developed, and to explore the relationship between these two factors. The results show that for different soil thicknesses, heat transfer coefficients are 0.1 m (0.76 W/m2·K), 0.2 m (0.624 W/m2·K), 0.3 m (0.53 W/m2·K), and 0.4 m (0.46 W/m2·K). The carbon emissions across the life cycle are as follows: construction phase (57.07 kg·m−2) > maintenance phase (36.08 kg·m−2) > material production phase (19.65 kg·m−2) > material transportation phase (14.15 kg·m−2) > daily usage phase (7.02 kg·m−2). Daily carbon emissions positively affect the heat transfer coefficient, while soil thickness has a significant negative effect. A green roof module with a combination of three plant types and a 0.3 m soil substrate presents the optimal parameters for reducing heat transfer. These findings have important implications for the design of green roofs in urban environments, suggesting pathways for optimizing energy efficiency and minimizing carbon footprints, thereby contributing to more sustainable urban planning.