# Experimental Investigation and Optimization of a Glazed Transpired Solar Collector
## 2 Materials and Methods
### Optimization of the GTC Design
#### 2.1.2 Results and Discussion  
* Meteorological data: The GTC experimental stand is located in the courtyard of the CAMBI Research Center laboratory, within the premises of the Faculty of Building Services Engineering--Technical University of Civil Engineering Bucharest. We present below the weather data for this location (66, Pache Protopopescu Boulevard--Bucharest: 44\({}^{\circ}\)26\({}^{\prime}\)22.8\({}^{\prime\prime}\) N 26\({}^{\circ}\)07\({}^{\prime}\)33.6\({}^{\prime\prime}\) E), recorded during the experimental studies. It should be noted that the reported data (Tables 2 and 3) represent average values during the interval 13:10-14:10 for each day of measurements (one day of experimental study corresponds to an air flow rate value for each configuration, 30 mm or 50 mm distance between the absorber and the glazing). \begin{table}
\begin{tabular}{c c c c c} \hline
**Instrument** & **Type** & **Parameter** & **Range** & **Uncertainty** \\ \hline Thermocouple & K (NiCr-Ni) & Temperature & \(-\)10...+105 \({}^{\circ}\)C & \(\pm\)0.2 \({}^{\circ}\)C \\ Air flow meter & FlowFinder mk2 & Air flow & 10... 550 m\({}^{3}\)/h & 3\% \\ Digital sensor & Almemo FHAD 46-C2 & Ambient temperature & \(-\)20...+60 \({}^{\circ}\)C & \(\pm\)0.2 \({}^{\circ}\)C \\ Cup-type anemometer & Almemo FVA 615 2 & Wind velocity & 0.5...50 m/s & 3\% \\ Wind vane & Almemo FVA 614 & Wind direction & 0..360\({}^{\circ}\) & \(\pm\)5\({}^{\circ}\) \\ Star pyranometer & Almemo FLA 628 S & Solar radiation intensity & 0...1500 W/m\({}^{2}\) & \(<\)3\% \\ \hline \end{tabular}
\end{table} 
Table 1: Measuring devices’ characteristics. Figure 3: Flow meter installation within the experimental set-up. This same study period (13:10-14:10) for each day was chosen because the solar radiation and outdoor air temperature have relatively constant values during all the days of the experimental study in this interval. In addition, the values of these climatic parameters are very close from one day to another in this interval (see Tables 2 and 3). This allows the exploitation and comparison of experimental results under relatively close weather conditions in order to obtain correct findings. * GTC thermal behavior: The GTC thermal behavior under different operating conditions can be evaluated by the following parameters: the difference between the GTC inlet air temperature and GTC outlet air temperature and the GTC absorber plate temperature. These data are presented in Tables 4 and 5 for each of the two GTC configurations considered. other hand, the rise in temperature of the air passing through the GTC was roughly 4-5 \({}^{\circ}\)C higher in the case of the GTC configuration with 30 mm distance between the absorber and the glazing for the same values of airflow rates. This is due to the modified space between the absorber and the glass layer, but it must also be taken into account that the experimental tests for the GTC configuration with a 30 mm air gap among the absorber and the glazing benefited from more important solar radiation intensities and higher ambient air temperatures on some days. Nevertheless, [PERSON] et al. [54] highlighted the same phenomenon: increased air layer thickness between the absorber and the glass affects the heat transfer within the solar collector due to an enhancement of heat losses through convection at the front (glazing) of the solar collector. * GTC performance evaluation: The heat transfer effectiveness of solar collectors can be evaluated using the following simplified calculation method [18]: \[\varepsilon_{HX}=\frac{T_{outlet}-T_{ambient}}{T_{plate}-T_{ambient}}\] (1) where \(T_{outlet}\)--outlet air temperature (\({}^{\circ}\)C); \(T_{ambient}\)--ambient air temperature (\({}^{\circ}\)C); and \(T_{plate}\)--absorber plate temperature (\({}^{\circ}\)C).