Modeling the heat diffusion process in the abiotic layers of green roofs

Jim, Chi Yung; Tsang, Sung

doi:10.1016/j.enbuild.2011.01.012

Cited by 61 publications

(19 citation statements)

References 16 publications

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“…The sensitivity test shows that an increase in soil moisture from 30% to 60% could reduce 24% of heat storage for green roofs. Recent researches indicate that the soil moisture availability is a key factor for the cooling efficacy of green roofs [39,40]. In this study, the theoretical calculations based on experimental results demonstrate that the cooling effect of soil water availability is similar to the empirical findings, thus verifying that water is important in reducing the solar energy penetration into the buildings.…”

Section: Results Of Sensitivity Analysissupporting

confidence: 80%

Theoretical evaluation of thermal and energy performance of tropical green roofs

Tsang

Jim

2011

Energy

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Section: Results Of Sensitivity Analysissupporting

confidence: 80%

Theoretical evaluation of thermal and energy performance of tropical green roofs

Tsang

Jim

2011

Energy

Self Cite

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“…A green roof with a continuous and vigorous vegetation cover is more important than vegetation type in reducing heat gain into buildings. This finding corroborates with that obtained in a focused study of the cooling effect of the abiotic layers in green roofs (Jim and Tsang 2011). This finding has important implications to the choice of green-roof materials and vegetation in the humid tropics.…”

Section: Resultssupporting

confidence: 81%

Effect of vegetation biomass structure on thermal performance of tropical green roof

Jim

2011

Landscape Ecol Eng

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The passive cooling effect of green roofs in humid, tropical Hong Kong was investigated with reference to three vegetated plots, grass, groundcover herb, and shrub, with contrasting growth form and biomass structure and a bare control plot. Temperature was monitored at 15-min intervals for a year at seven levels: high (H) at 200 cm, middle (M) at 60 cm, low (L) at 20 cm, surface, soil, rockwool (water storage), and roof-tile surface. The findings indicated the crucial roles played by biomass quantity and structural complexity in passive cooling functions. Temperature variations of vegetated roofs occurred mainly during the day, with lower maximum and minimum than the control, but they did not cool air at night better than the control. Control and grass surfaces were warmed above the ambient temperature, but groundcover and shrub surfaces followed the ambient. Despite complex biomass structure, shrub created the most extreme diurnal air temperature regime. Despite simple biomass structure, grass cooled air more effectively than groundcover and shrub. Four anomalies in the vertical temperature profile were detected. First, the grass roof cooled daytime nearground air to create a suspended temperature inversion. Second, the stagnant air within the shrub biomass trapped heat to generate a daytime canopy temperature inversion. Third, the elevated branch-foliage biomass of groundcover and shrub brought passive cooling to form a perched thermal discontinuity. Fourth, the air gap of the plastic drainage layer arrested downward heat transmission in all vegetated plots to form a subsurface thermal discontinuity.The findings provide hints on species choice and design of green roofs.

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“…This effect may vary depending on the climate conditions [22][23][24], and the level of insulation specially in cases of building retrofitting [25,26]. Most of these multiple benefits are linked to the cooling effect due to the evapotranspiration process (ET) that humidifies the external ambient air, reduces the surface temperature of the roof [27], and mitigates the urban heat island phenomenon [28].…”

Section: Introductionmentioning

confidence: 99%

The evapotranspiration process in green roofs: A review

Cascone

Coma

Gagliano

et al. 2019

Building and Environment

166

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Previous research has shown that most of the green roof benefits are related to the cooling effect. In the literature available, however, it is still not clear how and how much the evapotranspiration affects the performance of a green roof. In order to fill the gap in this research topic, this study carries out a review on the cooling effect due to the evapotranspiration process of green roofs. First of all, an overview of the evapotranspiration phenomenon in green roofs, as well as the equipment and methods used for its measurement are presented. Then, the main experimental results available in literature, the physicalmathematical models and the dynamic simulation software used for the evaluation of the latent heat flux are also analysed and discussed among the available literature. Moreover, this review proposes a classification of the results carried out by previous studies as function of the main parameters affecting the evapotranspiration process (e.g. volumetric water content, stomatal resistance, Leaf Area Index, solar radiation, wind velocity, relative humidity, soil thickness, and substrate composition). Additionally, a sensitivity analysis of the results obtained from the literature allowed underlining the correlation among the main factors affecting the evapotranspiration. Finally, a vision of the world area where green roof studies were performed is provided. From the results, it is possible to emphasize that most of the studies that evaluated the evapotranspiration used high precision load cells. Furthermore, all the heat transfer models of green roofs considered in this review took into account the latent heat flux due to evaporation of water from the substrate and plants transpiration, however, only few of them were experimentally validated.

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Modeling the heat diffusion process in the abiotic layers of green roofs

Cited by 61 publications

References 16 publications

Theoretical evaluation of thermal and energy performance of tropical green roofs

Theoretical evaluation of thermal and energy performance of tropical green roofs

Effect of vegetation biomass structure on thermal performance of tropical green roof

The evapotranspiration process in green roofs: A review

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