## 3 Results and Discussion
### Experimental Results
#### 3.2.3 Transient Thermal Model Results  
The first finding that has been observed in the transient thermal models was the importance of positioning the expanded clay layer appropriately within the green swale cross-section. As it can be seen in Figure 9, the thermal insulation reached at the lower part of the type 2 model under dry conditions was greater than the one registered when introducing the expanded clay in the intermediate layer instead of in the sub-base layer. This change in the cross-section arrangements of the dry swale layers would reduce the temperature in the area where the shallow geothermal conduits should be placed; after 10 days, it was as much as 0.535 \({}^{\circ}\)C below the value of the cross-section with the expanded clay placed in the sub-base.  
Therefore, the expanded clay in types 2 and 3 should be placed in the intermediate layer and the limestone aggregate and CDW is recommended to be placed in the sub-base layer.  
Figures 10 and 11 show the evolution of the temperature values at the bottom of green swales under dry and wet conditions, respectively. In both cases, it is possible to observe the improvement in the insulation capacity of the ground regarding with the outside ambient temperature in the dry swales in which expanded clay is used. On the one hand, the performance of type 2 and 3 green swales under dry conditions is reported to be rather similar, presenting final temperatures of 21.72 \({}^{\circ}\)C and 21.77 \({}^{\circ}\)C, respectively, which are lower than those registered in type 1 (22.27 \({}^{\circ}\)C). On the other hand, the drop in thermal insulation performance of the ground can be particularly noticed for the models performing under  
\begin{table}
\begin{tabular}{c c c} \hline \hline
**Thermal Conductivity (W/mK)** & **Dry Conditions** & **Wet Conditions** \\ \hline Vegetable land & 0.373 & 0.963 \\ \hline Limestone aggregates & 0.348 & 0.795 \\ \hline Expanded clay & 0.105 & 0.298 \\ \hline CDW & 0.315 & 0.711 \\ \hline \hline \end{tabular}
\end{table}
Table 9: Optimized equivalent thermal conductivity values of the materials of green swale layers.  
Figure 9: Temperatures at the bottom layer in type 2 green swale models under dry conditions based on the final location of the expanded clay within the cross-section.  
wet conditions. Likewise, it should also be highlighted that there were greater temperature variations at the bottom of the swales functioning under wet operating conditions, which will be more influenced by the ambient conditions outside. Temperatures of 22.78 \({}^{\circ}\)C, 22.52 \({}^{\circ}\)C, and 22.54 \({}^{\circ}\)C were reached for types 1, 2, and 3 model swales, respectively, under wet conditions.  
Figure 11: Comparison of the temperatures registered at the bottom of the green swale with the ambient temperatures under wet conditions.  
Figure 10: Comparison of the temperatures registered at the bottom of the dry swale with the ambient temperatures under dry conditions.  
The temperature in the lower part of the swales (where the GHE would be placed) increases during a 10-day period. The main reason is the accumulation of heat in the lower area close to the heat exchanger. In order to study this phenomenon correctly, it will be necessary to carry out field tests to help determine the dissipative effect of the soil under the dry swale and thus allowing for the calibration of the developed models.  
Even so, the temperature difference between the bottom of the swale and the ambient temperature was significant. In the worst scenario reported in this study, an increase of 2.77 \({}^{\circ}\)C in comparison with the initial temperature of 20 \({}^{\circ}\)C was registered at the bottom of the dry swale (see Table 10). A higher temperature difference between the ambient temperature and the GHE temperature would result in better performance of the GSHP [34].