Evaluation of the energy performance and irrigation requirements of extensive green roofs in a water-scarce Mediterranean climate

In urban areas, a considerable proportion of energy demand is allocated to buildings. Since rooftops constitute one-fourth of all urban surfaces, an increasing amount of attention is paid to achieving the most efficient shapes and component designs compatible with every climate and urban context, for rooftops of varying sizes. In this study, three types of rooftop technologies, namely insulated, green roof, and rooftop greenhouse, are evaluated for energy and thermal performance using computer simulations. Water surface exposure, absorption, and intrusion are the three important factors in the calculation of hygrothermal models that impact energy consumption and building envelope performance; however, a few studies are specifically focused on providing realistic results in multi-dimensional hygrothermal models and the assessment of the impact of moisture in roofing solutions. This paper aims at evaluating the performance of three different roofing technologies through a two-dimensional hygrothermal simulation in software WUFI. To accomplish this, a precise localized microclimate model of a complex urban context on the scale of a neighborhood was employed to evaluate the cooling and heating loads of the buildings, the impact of the water content in the green roof on the thermal behavior of the roof surface, and the feasibility of designing a building with nearly zero cooling needs. A two-story building in the city center of Bologna, Italy is modelled. Simulation results have shown that during the cooling period, the performance of the designed rooftop greenhouse is the most effective by 50% reduction in cooling loads. Besides, the impact of moisture in green roofs has been detected as a negative factor for thermal and energy performance of the building in the Mediterranean climate. The results ultimately highlighted the capability of passively-designed rooftop greenhouses to create a building with nearly zero cooling needs.

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The impact of extensive green roofs on the improvement of thermal performance for urban areas in Mediterranean climate with reference to the city of Jijel in Algeria

10.1063/1.5039250 ◽

2018 ◽

Cited By ~ 1

Author(s):

M. C. Lehtihet ◽

A. Bouchair

Keyword(s):

Thermal Performance ◽

Urban Areas ◽

Mediterranean Climate ◽

Green Roofs ◽

The Impact ◽

The City ◽

Extensive Green Roofs

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Green roofs energy performance in Mediterranean climate

Energy and Buildings ◽

10.1016/j.enbuild.2016.01.012 ◽

2016 ◽

Vol 116 ◽

pp. 318-325 ◽

Cited By ~ 76

Author(s):

Cristina M. Silva ◽

M. Glória Gomes ◽

Marcelo Silva

Keyword(s):

Mediterranean Climate ◽

Green Roofs ◽

Energy Performance

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Impact of Vegetation, Substrate, and Irrigation on the Energy Performance of Green Roofs in a Mediterranean Climate

Water ◽

10.3390/w11102016 ◽

2019 ◽

Vol 11 (10) ◽

pp. 2016 ◽

Cited By ~ 5

Author(s):

Gomes ◽

Silva ◽

Valadas ◽

Silva

Keyword(s):

Mediterranean Climate ◽

Energy Use ◽

Soil Depth ◽

Green Roof ◽

Green Roofs ◽

Energy Performance ◽

Area Index ◽

Vegetation Height ◽

Energy Needs ◽

Irrigation Levels

Green roof energy performance is still a challenging topic, namely in a Mediterranean climate since it depends on building characteristics, roof type, and also on climatic conditions. This paper evaluates green roof buildings’ energy needs and use in a Mediterranean climate. An experimentally calibrated numerical model was used to perform a parametric analysis and identify the influence of key parameters in heating and cooling energy needs, as well as annual energy use. The vegetation height, the soil depth, and LAI (leaf area index) were identified as the key parameters. The irrigation levels were also crucial for the energy performance of green roofs, particularly during the summer period and in a Mediterranean climate. Heating energy needs were mainly associated with soil depth due to higher thermal resistance, whereas cooling energy needs depended mostly on LAI, which influenced evapotranspiration and shading effects. A reduction of soil depth from 1.0 m to 0.1 m increased winter energy needs by up to 140%, while low values of LAI increased cooling energy needs up to 365%. Annual energy use in a Mediterranean climate showed a higher dependence on soil depth, with oscillations of up to 115%, followed by LAI and vegetation height. Finally, irrigation levels impacted the annual energy use more significantly for lower watering flow rates. Reductions of about 500% were obtained when changing watering flowrates from 0 mm/day to 6 mm/day in intensive green roofs. Since green roofs with native species expect low values of watering, this may increase their cooling energy needs.

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