# Experimental Investigation and Optimization of a Glazed Transpired Solar Collector
## 2 Materials and Methods
### Integration of the Optimized GTC into a Building Facade
#### 2.2.2 Results and Discussion  
* Meteorological data:  
We present below a sample of meteorological data recorded during the experimental campaign (Figure 11--intensity of the solar radiation and Figure 12--ambient temperature). As can be seen, there were major discrepancies regarding the weather conditions for the days when the measurements took place. For this reason, we selected for our analysis only the sequences of days with somewhat similar outside temperature and sunshine. For instance, one of the best such sequences for comparisons without/with a GTC is for the following days: 10 May 2021 and 11 May 2021 for the building without a GTC and 18 May 2021 for the building with a GTC. The diurnal variation in the solar radiation and air temperature for these days is shown in Figures 13 and 14, respectively. Figure 12: Outdoor temperature for several days during the experimental tests. Figure 13: Days chosen for analysis: solar radiation intensity. In addition, we present the mean values of the solar radiation and outdoor temperature for these days throughout the experiments in Table 7.  
GTC energy-saving assessment:  
In order to evaluate the GTC contribution to the energy saving of the experimental building, the following situations were analyzed: the energy required to heat the container using the air conditioner in heat pump mode (indoor temperature set-point: 22 \({}^{\circ}\)C), while the fresh air required for ventilation was supplied through the GTC or directly from outside. The results achieved for the three days mentioned above (without/with GTC) are shown in Table 8.  
It can be seen from the data in Table 8 that the energy savings due to preheating the ventilation air through the GTC were between 16 and 23% although the absolute difference in energy consumption seems very low (below 0.3 kWh). Furthermore, based on the experimental results concerning the air temperature rise through the GTC (installed on the facade of the container), the reduction in container ventilation load due to the GTC was determined for several days. This evaluation is based on the following expression:  
\[Q=V\rho c_{p}\big{(}T_{set-point}-T_{air}\big{)} \tag{3}\] \begin{table}
\begin{tabular}{c c c c} \hline \hline
**Parameter/Configuration (Day)** & **Without GTC** & **Without GTC** & **With GTC** \\  & **(10 May 2021)** & **(11 May 2021)** & **(18 May 2021)** \\ \hline ambient temperature (\({}^{\circ}\)C) & 18.9 & 18.8 & 21.8 \\ solar radiation intensity (W/m\({}^{2}\)) & 411 & 410 & 387 \\ \hline \hline \end{tabular}
\end{table} 
Table 7: Days chosen for analysis: weather data (average values). Figure 14: Days chosen for analysis: outside temperature. \begin{table}
\begin{tabular}{c c c c} \hline \hline
**Energy Consumption/Configuration (Day)** & **Without GTC** & **Without GTC (11 May 2021)** & **Without GTC** \\  & **(10 May 2021)** & **(2021)** & **(18 May 2021)** \\ \hline Container heating (kWh) & 1.12 & 1.23 & 0.94 \\ \hline \hline \end{tabular}
\end{table} 
Table 8: Heating energy consumption: experimental building without/with GTC. where \(V-\)ventilation airflow rate (m\({}^{3}\)/s); \(\rho-\)air density (kg/m\({}^{3}\)); \(c_{\rm p}-\)air specific heat capacity (J/kg/\({}^{\circ}\)C); \(T_{set-point}=\) container indoor temperature (\({}^{\circ}\)C); and \(T_{air}-\)ventilation (supply) air temperature (\({}^{\circ}\)C). The values used in Equation (3) are: ventilation airflow rate, 0.02 m\({}^{3}\)/s (72 m\({}^{3}\)/h as explained before); container indoor temperature, 22 \({}^{\circ}\)C (temperature set-point). On the other hand, the supply air temperature is either the GTC outlet air temperature or outdoor temperature, depending on whether or not the air is passing through the GTC. Consequently, the values of the ventilation air temperature in Equation (3) are, according to Table 9, dependent on the configuration (without/with GTC).