*4.2. Analysis of the WFG Cabin*

Two different mechanisms appeared to modify the thermal performances of the WFG. The first one was the value of the indoor temperature, which can be very high, depending on the wall insulation. The second one was the absorbed back irradiance. Depending on the insulation of the walls and the near-infrared absorptances, the water heat gain can differ when compared to the water heat gain of isolated glazing. Figure 15 shows the comparison between real data and simulation over the same day, 23 July 2018. MEs and MPEs of the indoor temperature of the WFG cabin were lower than 1.2 ◦C and 5.5%, respectively.

**Figure 15.** Indoor air temperature. Real results and simulation of the WFG cabin. Sample summer day 23 July 2018.

Figure 16 illustrates the time histories of indoor and outdoor air temperatures and the solar irradiance in W/m2 on the outdoor horizontal roof surface on a sample summer day (23 July 2018). The indoor air temperature of the Reference cabin (*Tr\_air*) varied according to the solar irradiance and the outdoor temperature (*T\_ext1*). The measured inlet temperature (*T\_inletI*) was input in the simulation tool as boundary conditions. By considering the activation of a solar fed "Peltier" device, the inlet temperature was set between 18 and 22 ◦C. The operation schedule for the cooling system activation was from 12:30 to 20:00. Figure 16 reports the results of the daily analysis. The thermal effect of the "Peltier" device kept the indoor temperature below 27 ◦C over the hottest hours of the day.

**Figure 16.** WFG cabin with the "Peltier" cell on from 12:30 to 20:00, 23 July 2018.

The daily cooling demands are shown in Figure 17. The daily energy that the flow of water can absorb was calculated using Equation (15). WFG prevented this energy from entering the cabin. The "Peltier" device provided the cooling power that explains the difference in temperatures between the WFG cabin and the Reference cabin. The energy absorbed by the WFG was 117.5 Wh in 0.5 m2, so the ratio of energy per area was 0.235 kWh/m2.

**Figure 17.** WFG cabin with the "Peltier" cell on from 12:30 to 20:00, 23 July 2018. Absorbed power *mc( ˙* <sup>θ</sup>*IN*−θ*OUT)* in *<sup>W</sup>*/*m2.*
