Abstract
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.
Highlights
Green roofs are roofs covered with vegetation and a growing medium
The results show that decreasing the soil density from 1500 to 300 kg/m3 increased the annual energy use by 0.4% for irrigation of 6 mm/day and decreased it by 0.3% for 0 mm/day of irrigation
This paper evaluated the energy performance of green roofs in a Mediterranean climate by
Summary
Green roofs are roofs covered with vegetation and a growing medium. Beneath the growing medium and above the structural support (mostly depending on building age), the constructive system may be composed of a waterproofing membrane, root barrier, drainage, and insulation [1].The green roofs are classified into three types [2]: extensive, intensive, and semi-intensive.The extensive roof is characterized by a thin growing medium (6–25 cm), small plants, light, and requires minimal maintenance. Green roofs are roofs covered with vegetation and a growing medium. Beneath the growing medium and above the structural support (mostly depending on building age), the constructive system may be composed of a waterproofing membrane, root barrier, drainage, and insulation [1]. The green roofs are classified into three types [2]: extensive, intensive, and semi-intensive. The extensive roof is characterized by a thin growing medium (6–25 cm), small plants, light, and requires minimal maintenance. The intensive roof is characterized as requiring more maintenance, supports a wider variety of plants, and is be heavier and thicker (15–70 cm) than the extensive roof. The semi-intensive roof has intermediate characteristics between the intensive and extensive roofs
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