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Green roofs are known for their beneficial aspects on the buildings energy consumption and the environment quality. However, the lack of precise knowledge of thermal, water, botanic characteristics is an obstacle to predict theirs efficiencies in the case of construction projects. In this study, three of the main physical properties of green roofs were experimentally investigated to determine some of the key green roof modeling parameters. First, the thermo-physical properties of green roofs were characterized by correlating the thermal conductivity of the substrate with the water content for different maximum water capacities. Also, the thermal resistance of green roof was evaluated in controlled weather conditions using a low speed wind tunnel. Next, the moisture storage was characterized using the dynamic vapor sorption technique to determine both of sorption and desorption isotherms as well as the moisture buffer capacity. Third, the microstructural properties of green roof substrate were characterized using mercury intrusion porosimetry to measure the porosity range of green roof substrate. The experimental results were used to estimate the parameters used as input data in the developed green roof model to evaluate the energy performance of a building. [ABSTRACT FROM AUTHOR]

Highlights: [•] Evaporation and transpiration were evaluated separately. [•] The thermal resistance of green roofs was evaluated using a low-speed wind tunnel. [•] The impact of grey water on evapotranspiration and green roof thermal resistance was studied. [ABSTRACT FROM AUTHOR]

Abstract: In this study, three of the main physical properties of green roofs were experimentally investigated to determine some of the key green roof modeling parameters. First, the thermo-physical properties of green roofs were characterized by correlating the thermal conductivity of the substrate with the water content for different substrates and maximum water capacities. Next, the moisture storage was characterized using the dynamic vapor sorption technique to determine both the sorption and desorption isotherms for three different temperatures as well as the moisture buffer capacity. Third, the micro-structural properties of green roof substrate were characterized using mercury intrusion porosimetry to measure the porosity range of the substrate and to compare this porosity range with different concrete porosities. In addition to these characterizations, the evapotranspiration term, which is very important in the water balance, was measured. The few studies found in literature provide the expression of the evapotranspiration term for a watered grass and vegetated areas on a large scale. In this study, this term is expressed for the experimentally studied green roof complex (substrate + vegetation). The ultimate objective of these experiments is to estimate the parameters used as input data in the developed green roof model to evaluate the energy performance of a building. [Copyright &y& Elsevier]

Abstract: This paper describes a dynamic model of transient heat and mass transfer across a green roof component. The thermal behavior of the green roof layers is modeled and coupled to the water balance in the substrate that is determined accounting for evapotranspiration. The water balance variations over time directly impact the physical properties of the substrate and the evapotranspiration intensity. This thermal and hydric model incorporates wind speed effects within the foliage through a new calculation of the resistance to heat and mass transfer within the leaf canopy. The developed model is validated with experimental data from a one-tenth-scale green roof located at the University of La Rochelle. A comparison between the numerical and the experimental results demonstrates the accuracy of the model for predicting the substrate temperature and water content variations. The heat and mass transfer mechanisms through green roofs are analyzed and explained using the modeled energy balances, and parametric studies of green roof behavior are presented. A surface temperature difference of up to 25°C was found among green roofs with a dry growing medium or a saturated growing medium. Furthermore, the thermal inertia effects, which are usually simplified or neglected, are taken into account and shown to affect the temperature and flux results. This study highlights the importance of a coupled evapotranspiration process model for the accurate assessment of the passive cooling effect of green roofs. [Copyright &y& Elsevier]

Abstract: Green roofs have a positive effect on the energy performance of buildings, providing a cooling effect in summer, along with a more efficient harnessing of the solar radiation due to the reflective properties found inside the foliage. For assessing these effects, the thermodynamic model was developed as well as the thermo-physical properties of the green roof components were characterized. Its typologies and vegetation styles should also be studied. The proposed model is based on energy balance equations expressed for foliage and soil media. In this study, the influence of the mass transfer in the thermal properties and evapotranspiration were taken into account. We then added the water balance equation into our model and performed a numerical simulation. By assuming the outdoor conditions, the roof support temperature and the drainage water as inputs, the model evaluates the temperatures evolution at foliage and soil ground levels. A parametric study was performed using the proposed model to classify green roofs depending on the considered climate condition. Comparisons were undertaken with a roof slab concrete model; a significant difference (of up to 30 °C) in temperature between the outer surfaces of the two roofs was noticed in summer. The model was experimentally validated according to green roof platform, which was elaborated. The mass transfer effect in the subtract was very effective in reducing the model errors. Simulation results show that the use of vegetation in the roof building improves not only thermal comfort conditions, but the energy performance of a building. [Copyright &y& Elsevier]