Natural ventilation and passive cooling for energy efficiency of residential buildings in Mediterranean climate

The upcoming new energy requirements for European buildings impose Nearly Zero Energy standards within few years. In order to achieve such a result, new buildings will need to combine high performance envelopes, energy-efficient active energy systems, on site renewable energy production and passive systems. The latter seem the most difficult to be widely implemented in the conventional buildings, despite their proven effectiveness. Particularly, natural and hybrid ventilation systems in Mediterranean climate have a huge potential in terms of energy savings and indoor comfort improvement. The main obstacles for a wider use of such systems lie probably in difficulties and uncertainties inherent in the design and in the predictability of actual performance. The article describes a methodology to overcome these problems and presents two case studies that illustrate the process and give an example of the possible results. The design process is articulated through the use of analysis and simulation tools, progressively more detailed. So the general strategies are adapted to the climate and the main building features; site and general building design depend on the microclimate specific characteristics; detailed design and systems calibration are defined on the basis of internal CFD and sub hourly energy simulations. Likewise, other aspects of passive design, such as solar systems, are determined through a similar process of progressive deepening by means of specific simulation tools. The case studies, two public housing buildings in Tuscany (Italy), are designed on a high energy standard, with passive solar systems, natural and hybrid ventilation strategies, high-efficiency systems, integrated photovoltaic modules and, in one instance, a solar cooling system. The design process and the estimated performance are illustrated with particular regard to ventilation and cooling systems. The buildings are expected to have very low energy consumption and a high quality standard for the indoor comfort, showing a good potential for these strategies in Mediterranean climate. Namely, the cooling needs are reduced by a quantity between 74 to 100%, meaning that an effective ventilation systems (combined with other strategies, can get to completely eliminate the need of mechanical cooling