## 2 Experimental Description  
The study was carried out for a single-story facade built on the southwest face of the INCERC Laboratory of Applied Research and Testing in Constructions, National Institute of Research and Development URBAN-INCERC lasi, a city in the north-east of Romania (Figure 1). The test facility was designed for thermal and airflow investigations of the DSF performance, functioning under natural or mechanical conditions and using various ventilation principles (outdoor air curtain, indoor air curtain, air supply, air exhaust, buffer zone) [37]. The experimental double-skin facade measured 2.0 m width by 2.8 m high and included the double skin glass facade and an interior room (Figure 2). The inner skin of the facade was a 24 mm thick double-insulated glass and the outer one was a single 12 mm  
Figure 1: View of the double-skin facade: (**a**) from the outside of the building and (**b**) from the inside of the interior room. thick clear glass pane. The central part of the inner skin was designed to be opened and to facilitate access to the channel for experimental testing, cleaning, and maintenance purposes. The external skin was composed of two fixed parts of simple glazing for reasons of mechanical resistance. The air cavity between the two glazing panes was 0.45 m wide. Two openings were included in the exterior glazing of DSF, one for the air inlet located at the bottom of the facade and one for the air outlet in the upper part. The openings for ventilation with 0.1 m high cover the whole width of the stand. The interior room measures 2.0 m wide, 2.8 m high, and was 1.75 m in width and was very well insulated to reduce the influence of the indoor environment on the facade (Figure 2a). Using a cooling unit, the temperature of the test chamber was kept constant (\(27\pm 0.5\,^{\circ}\)C) starting on day 3 of each summer period (SET1-3). The interior chamber was left unconditioned for the first two days of these periods. For this experiment, no sun-shading device systems were used. The DSF materials and construction details and thermal and optical properties are presented in Table 1.  
The experimental campaigns included four periods specific to the climate in Romania: three periods in the hot season of July corresponding to three modes of air curtain ventilation (ascendant air circulation between the exterior inlet and exterior outlet sections) and one period in the cold season of November for the buffer mode of DSF (closed air channel), Figure 3.  
In the first period (SET 1: 7 th-13 th July), the exterior air inlet and the exterior air outlet were open, and natural ventilation occurred inside the channel. In the second period (SET 2: 14 th-20 th July), due to the overheating problem that occurred inside of the DSF channel, the cavity was mechanically ventilated by adding three VORTICE fans in the upper opening of the exterior facade, each with a flow rate of \(85\,\mathrm{m}^{3}/\mathrm{h}\) (SET 2) and an electrical power of 15 W. The choice of the ventilation air rates was based on the criterion of minimum energy consumption of the fans. A higher air flow rate will cool the channel better but with more energy consumption, which will lower the benefits of the system. \begin{table}
\begin{tabular}{c c} \hline \hline
**Component** & **Properties** \\ \hline \multirow{3}{*}{Exterior glazing} & single pane (8 mm), clear float glass, central glass \\  & U-value = 5.6 W/(m\({}^{2}\cdot\)K), transmission \(\tau\) = 82\%, absorption \(\alpha\) = 11\%, solar \\  & reflection \(\rho\) = 7\%. \\ \multirow{3}{*}{Exterior frame} & aluminum frame with thermal barrier, U-value = 3.1 W/(m\({}^{2}\cdot\)K) \\  & double thermo-insulated pane glazing (4-16-4 mm), clear float glass, low-E \\ \multirow{3}{*}{Interior glazing} & coating, central glass U-value = 1.92 W/(m\({}^{2}\cdot\)K) \\  & PVC frame with thermal barrier, U-value = 1.42 W/(m\({}^{2}\cdot\)K) \\ \hline \hline \end{tabular}
\end{table} 
Table 1: Thermal and optical properties of DSF glass.