scholarly journals Numerical Study of Heat and Water Vapour Exchanges Inside a Green Roof Building in a High Irradiation Area for Passive Cooling Purpose

2021 ◽  
Vol 1 ◽  
Author(s):  
Hodo-Abalo Samah ◽  
N’Detigma Kata ◽  
Kodjo Kpode ◽  
Magolmèèna Banna ◽  
Belkacem Zeghmati
Keyword(s):  
Heat Flux ◽  
Mixed Convection ◽  
Leaf Area Index ◽  
Leaf Area ◽  
Indoor Air ◽  
Numerical Study ◽  
Green Roof ◽  
Passive Cooling ◽  
Area Index ◽  
Solar Heat Flux

Vegetation cover provides shading and protects the soil beneath them from warming.  Vegetation can be used as passive cooling technique that reduces the thermal load of a building. A numerical study has been carried out on laminar double-diffusive mixed convection in a green roof enclosure. The model is equipped with inlet and outlet openings for air removal while the left vertical wall is heated and partially saturated with water for indoor air humidification. The mathematical model is governed by the two-dimensional continuity, momentum, energy and concentration equations. Transfer equations are solved using a finite difference scheme and Thomas algorithm. The model was applied for the simulation of a building with green roof in Togolese climate conditions. Results showed that, the flow structure is a mixed convection type, but the isotherms et iso-concentration distributions reveal a vertical stratification of the temperatures and the relative humidity.To predict heat transfers inside the cavity, a correlation has been established for the estimation of the average Nusselt number as a function of the Leaf Area Index and Reynolds number under solar heat flux of 350 W.m-2, the average in case of Togo. It was found that a larger Leaf Area Index reduces the solar flux penetration and therefore, reduces significantly heat transfer inside the enclosure and then stabilizes it temperature. For the LAI equal to 3, the indoor air fluctuates around 26°C and the relative humidity range is found to be 50% - 60% under solar heat flux of 350 W.m-2.

scholarly journals Representing winter wheat in the Community Land Model (version 4.5)

2017 ◽  
Vol 10 (5) ◽  
pp. 1873-1888 ◽  
Author(s):  
Yaqiong Lu ◽  
Ian N. Williams ◽  
Justin E. Bagley ◽  
Margaret S. Torn ◽  
Lara M. Kueppers
Keyword(s):  
Heat Flux ◽  
Winter Wheat ◽  
Leaf Area Index ◽  
Leaf Area ◽  
Latent Heat Flux ◽  
Carbon Allocation ◽  
Net Ecosystem Exchange ◽  
Area Index ◽  
Community Land Model ◽  
The Us

Abstract. Winter wheat is a staple crop for global food security, and is the dominant vegetation cover for a significant fraction of Earth's croplands. As such, it plays an important role in carbon cycling and land–atmosphere interactions in these key regions. Accurate simulation of winter wheat growth is not only crucial for future yield prediction under a changing climate, but also for accurately predicting the energy and water cycles for winter wheat dominated regions. We modified the winter wheat model in the Community Land Model (CLM) to better simulate winter wheat leaf area index, latent heat flux, net ecosystem exchange of CO2, and grain yield. These included schemes to represent vernalization as well as frost tolerance and damage. We calibrated three key parameters (minimum planting temperature, maximum crop growth days, and initial value of leaf carbon allocation coefficient) and modified the grain carbon allocation algorithm for simulations at the US Southern Great Plains ARM site (US-ARM), and validated the model performance at eight additional sites across North America. We found that the new winter wheat model improved the prediction of monthly variation in leaf area index, reduced latent heat flux, and net ecosystem exchange root mean square error (RMSE) by 41 and 35 % during the spring growing season. The model accurately simulated the interannual variation in yield at the US-ARM site, but underestimated yield at sites and in regions (northwestern and southeastern US) with historically greater yields by 35 %.

scholarly journals VEGETATION INSULATION SCREEN AS A PASSIVE COOLING SYSTEM IN HOT HUMID CLIMATE: HEAT AND MASS EXCHANGES

2021 ◽  
Vol 9 (10) ◽  
pp. 1368-1378
Author(s):  
Hodo-Abalo Samah ◽  
◽  
Magolmeena Banna ◽  
Belkacem Zeghmati ◽  
◽  
...  
Keyword(s):  
Leaf Area Index ◽  
Leaf Area ◽  
Cooling System ◽  
Gain Factor ◽  
Passive Cooling ◽  
Humid Climate ◽  
Heat Gain ◽  
Area Index ◽  
Solar Heat ◽  
Solar Heat Gain

Planted roofs are passive cooling techniques that reduce the thermal load of buildings. In this paper, a Dynamic mathematical model based ontime average Navier-Stokes equationsfor a plantedroof in hothumidclimates has beendeveloped for evaluating the cooling potential.Transfer equations are solved using a finite difference scheme and Thomas algorithm. The model was applied for the simulation of a planted roof in Togolese climate conditions. Results showed that, evapotranspiration and Solar Heat gain Factor are functions of the Leaf Area Index LAI which is the most important parameter when considering the foliage material. For LAI equal to 6, latent heat peak value reaches 900 W.m-2while that of sensible heat is around 350 W.m-2. Solar heat gain factor can bereducedto 15% fortheplantedroofagainst 45% forbareroof. It is clearly proved that the foliage density and hence the vegetation canopy type selection greatly influence the thermal efficiency of the bioclimatic insulation screen. A larger Leaf Area Index reduces the solar flux penetration and increases evapotranspiration which is an important parameter when considering surrounding microclimate formation.

scholarly journals Effects of Extensive Green Roofs on Energy Performance of School Buildings in Four North American Climates

Water ◽  
2019 ◽  
Vol 12 (1) ◽  
pp. 6 ◽  
Author(s):  
Milad Mahmoodzadeh ◽  
Phalguni Mukhopadhyaya ◽  
Caterina Valeo
Keyword(s):  
Leaf Area Index ◽  
Leaf Area ◽  
Plant Height ◽  
Green Roof ◽  
Green Roofs ◽  
Energy Performance ◽  
Design Parameters ◽  
Soil Thickness ◽  
Area Index ◽  
Roof Design

A comprehensive parametric analysis was conducted to evaluate the influence of the green roof design parameters on the thermal or energy performance of a secondary school building in four distinctively different climate zones in North America (i.e., Toronto, ON, Canada; Vancouver, BC, Canada; Las Vegas, NV, USA and Miami, FL, USA). Soil moisture content, soil thermal properties, leaf area index, plant height, leaf albedo, thermal insulation thickness and soil thickness were used as design variables. Optimal parameters of green roofs were found to be functionally related to meteorological conditions in each city. In terms of energy savings, the results showed that the light-weight substrate had better thermal performance for the uninsulated green roof. Additionally, the recommended soil thickness and leaf area index for all four cities were 15 cm and 5 respectively. The optimal plant height for the cooling dominated climates is 30 cm and for the heating dominated cities is 10 cm. The plant albedo had the least impact on the energy consumption while it was effective in mitigating the heat island effect. Finally, unlike the cooling load, which was largely influenced by the substrate and vegetation, the heating load was considerably affected by the thermal insulation instead of green roof design parameters.

scholarly journals Sensitivity of ground heat flux to vegetation cover fraction and leaf area index

1999 ◽  
Vol 104 (D16) ◽  
pp. 19505-19514 ◽  
Author(s):  
Z-L. Yang ◽  
Y. Dai ◽  
R. E. Dickinson ◽  
W. J. Shuttleworth
Keyword(s):  
Heat Flux ◽  
Leaf Area Index ◽  
Leaf Area ◽  
Vegetation Cover ◽  
Area Index ◽  
Ground Heat Flux

scholarly journals Plant- and Soil-Parameter-Caused Uncertainty of Predicted Surface Fluxes

2005 ◽  
Vol 133 (12) ◽  
pp. 3498-3516 ◽  
Author(s):  
Nicole Mölders
Keyword(s):  
Heat Flux ◽  
Leaf Area Index ◽  
Leaf Area ◽  
Stomatal Resistance ◽  
Surface Fluxes ◽  
Critical Parameters ◽  
Net Radiation ◽  
Area Index ◽  
Vegetation Fraction ◽  
Ground Heat Flux

Abstract Simulated surface fluxes depend on one or more empirical plant or soil parameters that have a standard deviation (std dev). Thus, simulated fluxes will have a stochastic error (or std dev) resulting from the parameters’ std dev. Gaussian error propagation (GEP) principles are used to calculate the std dev for fluxes predicted by the hydro–thermodynamic soil–vegetation scheme to identify prediction limitations due to stochastic errors, parameterization weaknesses, and critical parameters, and to prioritize which parameters to measure with higher accuracy. Relative errors of net radiation, sensible, latent, and ground heat flux, on average, are 7%, 10%, 6%, and 26%, respectively. The analysis identified the parameterization of thermal conductivity as the dominant influence on the std dev of ground heat flux. For net radiation, critical parameters are vegetation fraction and ground emissivity; for sensible and latent heat fluxes, vegetation fraction. Minimum stomatal resistance and leaf area index dominate the std dev of stomatal resistance for most vegetation and soil types. The empirical parameters with the highest relative error are not necessarily the greatest contributors to the std dev of the predicted flux. Based on the analysis high priority should be given to measurements of vegetation fraction, ground emissivity, minimum stomatal resistance, leaf area index in general, and the permanent wilting point and field capacity for clay and clay loam. Moreover, further specification of clay-type soils and tundra-type vegetation may improve the accuracy of the lower boundary condition in Arctic numerical weather prediction. Since GEP showed itself able to identify critical parameters and (parts of) parameterizations, GEP analysis could form a basis for parameterization intercomparisons and for parameter determination aimed at improving models.

Green roof simulation with a seasonally variable leaf area index

2018 ◽  
Vol 174 ◽  
pp. 156-167 ◽  
Author(s):  
L.W. Zhou ◽  
Qi. Wang ◽  
Y. Li ◽  
M. Liu ◽  
R.Z. Wang
Keyword(s):  
Leaf Area Index ◽  
Leaf Area ◽  
Green Roof ◽  
Area Index
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