Green roof heat transfer coefficient measurement and impact of plant species and moisture

Abstract

Green roofs attract wide attention for building energy conservation and sustainable development. However, the heat transfer coefficient of green roofs is not well defined. In this study, we developed a non-contact steady-state method for green roof heat transfer coefficient measurement. The apparatus required 16 min to reach the steady state, with a measurement variation of 2.84 ∼ 3.47 %. The impacts of plant species and substrate moisture on the heat transfer coefficient of green roofs were defined. The green roof with Sedum lineare (a CAM plant) performed the widest variation of heat transfer coefficient, from 2.847 W/m2 K (at the wilting point) to 5.401 W/m2 K (at the field capacity). The green roof with Paspalum vaginatum (a C4 plant) performed the least variation of heat transfer coefficient, with only 2.807 ∼ 3.069 W/m2 K from the wilting point to the field capacity. The green roof with Festuca arundinacea showed mediate variation in heat transfer coefficient, with 2.849 ∼ 4,372 W/m2 K. This work provides a method to determine green roof heat transfer coefficient and defined dynamics of heat transfer coefficients in three different green roofs, which is crucial to further elucidate the green roof heat transfer mechanism and the impact factors.