Building climate control by means of passive systems

Nowadays the growth of the cities increased built and paved areas, energy use and heat generation. The phenomenon of urban warming, called urban heat island, influences nega-tively outdoor comfort conditions, pollutants concentration, energy demand for air condition-ing, as well as increases environmental impact due to the demand of energy generation. In-door air temperature depends on a combination of several different parameters related to the climate of the region, the building itself and its use. The main parameters influencing the mi-croclimate are: external air temperature and relative humidity, incident solar radiation, long wave radiation exchange between the structure and its surroundings, incidence and speed of the wind, air exchanges, physical and thermal properties of the building’s envelope materials, design variables such as building dimensions and orientation, presence of artificial light, and electrical equipment. In the Mediterranean region the main problem is to control the solar heat gain that increases building’s temperature during the hot season. Solar heat is trans-ferred to the internal air through the envelope by the heat transfer mechanisms as conduc-tion, convection and radiation. Solar heat can be reduced by increasing the insulation be-tween the exterior and interior of the building, shading the building surface from direct sun exposure, by using an adequate building’s envelope materials or by using green roofs and walls. The use of green roofs and walls can contribute to mitigate the phenomenon of heat island, the emissions of greenhouse gases, and the storm water runoff affecting human thermal comfort, air quality and energy use of the buildings. Aim of this paper is to describe the benefits, the design requirements and plants, and the heat transfer mechanism of green roofs and walls. Green roofs and green vertical systems can be used as passive energy sav-ings systems because they intercept solar radiation by the vegetation, provide thermal insu-lation by the vegetation and substrate, occur evaporative cooling by evapotranspiration from the plants and the substrate, and influence the effect of the wind on the building.