In summer (over +22°C) the functioning of the double facades is aimed at minimizing the greenhouse effect, which occurs in between the two walls, since these can lead to the overheating

of the inter-facade void, with its temperatures exceeding those of the external wall. In order to avoid such a situation it is necessary to [10]:

• use adequate sunshades,

• force intensive air circulation in the inter-facade area,

• cool the building at night through the opening of windows,

• use buffer spaces (such as atriums) and elements with large thermal mass (constructions, water reservoirs).

Sunshades are placed between the two walls of the facade This protects them from the impact of atmospheric conditions, while retaining their efficiency. While in the winter period the circulation of air in the inter-facade void is limited to achieve energy gains, in summer only an intensive circulation of air protects it from overheating. The ventilation ducts in the external wall should be fully opened.

An increase in temperature, which occurs in between the walls causes the speed of the circulating air to increase, so this air is replaced more quickly. However, this increase is not proportional to heat increase [4]. When external air temperatures are high enough, hot air can become trapped inside the inter-facade void, leading to significant overheating of rooms. It then becomes necessary to boost the system with mechanical ventilation and air conditioning.

Double-facade walls allow for night cooling of the building through opening all windows in the internal wall. The external wall protects the interior from the wind and prevents intrusion into the building through open windows. At night, when outside temperature is much lower than during the day, the interiors are able to cool down. The effectiveness of this cooling is greater if the building can store it through internal buffer zones and construction elements, which have a large thermal mass.