## 4 Conclusions
On the other hand, for smaller solar radiation intensity of 20 W/m\({}^{2}\), the difference drops to around 2 \({}^{\circ}\)C. In this condition, the negative values of the pre-heating efficiency showed that the only benefit obtained from the ventilated facade is to increase the surface temperature of the inner glass pane inside the channel and reduce the heat losses from the interior room. On the other hand, the condensation appearance on the interior DSF surfaces was observed when the humidity reached values above 80% between 06:00 p.m. and 10:00 a.m. Results related to the summer period showed that the air and enclosing surfaces temperatures in the channel can reach values above 40 \({}^{\circ}\)C mainly between 10:00 a.m. and 02:00 p.m. due to the location and facade orientation, with a difference of about 12 \({}^{\circ}\)C relative to the exterior temperature, when the intensity of solar radiation reaches more than 500 W/m\({}^{2}\). Direct solar radiation intensity influences the increase of air temperature in the channel, even when the exterior temperature does not exceed 30 \({}^{\circ}\)C. In the evening and during the night, the two temperatures become almost equal with a difference of around 2 \({}^{\circ}\)C for one of the channels. The forced ventilation does not reduce the channel air and surface temperatures for the flow rates studied, but it can improve the cooling when no solar radiation is present. On the other hand, using a controlled mechanical ventilation system involves operating costs, energy consumption, and the need for an often complex system of technical management. The average air relative humidity in the channel was recorded around 48% and no risk of condensation phenomena was observed. The supplementary opening at the top of the channel improves the natural ventilation and the temperature difference between the channel and the ambient drops by around 9 \({}^{\circ}\)C at the noon and 1 \({}^{\circ}\)C during the night. A time shift of approximately one hour exists between the highest solar radiation and the maximum temperature recorded in the channel. In summer, the risk of overheating the DSF channel is obvious. Still, it can be minimized by using natural ventilation with good-sized inlets and outlets, combining the vertical with horizontal ones. The airflow analyses during the summer showed that its velocity at the inlet section depends on the wind speed and a higher temperature inside the channel determines higher velocities in natural convection. The forced ventilation mode determines the turbulent character of the flow in the middle of the channel with a variation of velocities between 0.25-0.42 m/s. This was confirmed by the visualizations of the airflow pattern inside the channel's median section, which highlighted an ascendant flow near the interior double glazing of the DSF channel and a descendant one near the exterior glazing. The performance indicator specific for the hot season in terms of dynamic insulation efficiency recorded a value of 71.3% for natural ventilation with both openings on the lateral outer glass and the vertical one at the top of the channel. Thus, in order to prevent the overheating of the facade during the hot season, combining vertical and horizontal openings in natural ventilation give the best efficiency of the double-skin facade functioning. Conceptualization, M.L.C. and N.C.C. ; methodology, M.L.C., N.C.C. and A.A.C. ; validation, N.C.C. and M.L.C. ; formal analysis, M.L.C., N.C.C., A.A.C. and S.V.H. ; investigation, M.L.C., N.C.C., A.A.C., S.V.H., E.F.T., A.B. and C.G.P. ; resources, M.L.C., N.C.C., A.A.C. and C.G.P. ; data curation, N.C.C. and S.V.H. ; writing--original draft preparation, N.C.C., M.L.C., A.B., S.V.H. and E.F.T. ; writing--review and editing, N.C.C. and M.L.C. ; visualization, N.C.C., S.V.H. and E.F.T. ; supervision, M.L.C. and N.C.C. ; project administration, N.C.C. and M.L.C. ; funding acquisition, N.C.C. and M.L.C. All authors have read and agreed to the published version of the manuscript.