## 5 Model Validation, Results and Discussion  
The calculations were performed with a time step equal to that of the data acquisition, i.e., 5 min, over a one-week duration. Figures 10 and 11 show respectively the comparison of numerical and experimental heat fluxes and temperatures on both sides of the storage wall (cement mortar + PCM). The composite Trombe wall was equipped with fluxmeters and thermocouples in order to measure the fluctuation in heat flux and temperature. When the solar flux radiation reaches its highest intensity, varying from 950 to 1000 W/m\({}^{2}\) (Figure 5), the storage wall can absorb a large quantity of incoming solar flux (400-450 W/m\({}^{2}\) of heat flux at the external surface of the storage wall), corresponding to about 50% of the incident solar radiation during sunshine hours. This percentage confirms the transmission rate measurements conducted in our laboratory with two pyranometers placed on both sides of the double glazing. The heat flux becomes negative (\(-\)50 W/m\({}^{2}\)) at the outer surface of the storage wall by the end of the day due to heat losses into the external environment. It should be noted here that the semi-transparent cover is a conventional double glazing; a glass with reinforced insulation would certainly have made it possible to limit these heat losses. The time lag between the incident solar radiation and the heat flux release in the ventilated air layer (\(\phi_{\rm int}\)), for this 4-cm thick experimental storage wall, is estimated by calculating the cross-correlation function [24] at 184 min (i.e., approximately 3 h). During sunny periods, the storage wall temperature can reach 65 \({}^{\circ}\)C on the outer surface and 45 \({}^{\circ}\)C on the inner surface. The difference between the heat fluxes at the outer surface of the storage wall \(\phi_{\rm ext}\), as calculated by the numerical method and measured by the fluxmeters (sum of the absolute values of the heat fluxes) equals 2.2%. This value is on the order of 8.6% of the difference evaluated between the calculations and measurements of heat fluxes on the inner surface of the storage wall, \(\phi_{\rm int}\). The average difference between the calculated and measured temperatures on the outer and inner surfaces of the storage wall (T\({}_{\rm ext}\) and T\({}_{\rm int}\)) is on the order of 1 \({}^{\circ}\)C. The difference of 8.6% between the calculated and measured flows on the inner side of the storage wall is due to the less accurate estimation of temperature on this surface, which is especially true at maximum temperatures. This difference is most probably due to the unidirectional (1D) calculation of heat transfers in the wall; consequently, heat losses towards the edges of the storage wall are not being taken into account. Moreover, the difference between numerical calculation and thermocouple measurement of the air temperature at the upper vent level of the ventilated air layer T\({}_{\rm uv}\) is on average 0.4 \({}^{\circ}\)C. In Figure 11, the released latent heat can be observed every day around 8:00 pm by the inflection of temperature curves at 26 \({}^{\circ}\)C, corresponding to the solidification point. Figure 12 illustrates air temperature variations at the inlet (T\({}_{\rm IV}\)) and outlet (T\({}_{\rm uv}\)) of the ventilated air layer, as well as the ambient temperature of the room (T\({}_{\rm room}\)). When the average temperature of air inside the ventilated air layer is higher or warmer than the room air temperature, a natural thermocirculation is thus activated, with air entering through the lower vent (T\({}_{\rm IV}\)) and being released from the upper vent (T\({}_{\rm uv}\)). This phenomenon is due to the thermal contributions of the storage wall in the ventilated air layer (convection and radiation), which in turn cause the air to be heated and then set into motion (i.e., a thermosiphon or \"chimney effect\").