Passive systems to control microclimate inside buildings

The phenomenon of urban warming, known as urban heat island, negatively influences outdoor comfort conditions and pollutants concentration, as well as increases the environmental impact due to the energy demand for air conditioning. In Mediterranean climate regions the main problem is to control the solar heat gain, that increases building’s temperature during the hot season, in order to protect the conditions of well-being of those who live or work in the buildings. Solar heat can be mainly reduced by increasing the insulation between the exterior and interior of the building, as well as shading the building surface from direct sun exposure. A sustainable technology for improving the energy efficiency of buildings is the use of green roofs and green walls in order both to reduce the energy consumption for conditioning in summer by physically shading the building structures and by promoting evapotranspiration, and to increase the thermal insulation in winter. Aim of this paper is to describe the green roofs and walls design requirements and to develop an energetic model capable of simulating the energy exchanges that take place in the presence of roofs / green walls. The energy model of the microclimate inside a building covered with plant species in Mediterranean climate depends on several different parameters that influence the indoor building microclimate such as 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. The model takes into account also the effect of different plant species. Solar heat is transferred to the internal air through the envelope by the heat transfer mechanisms as conduction, convection and radiation. The physical properties of the surface, such as the solar reflectance, infrared emittance and the convection coefficient, influence the surface temperature. 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 consumption in buildings.