## 6 Results and Discussions  
### The Lambeth College Case  
According to the discussion before, as the temperature changes in the heating/cooling trial, the heat transfer coefficient \(h\) should perform relevant change. Hence to get a matching curve, the \(h\) value should be altered in the heating/cooling. However, in the back-analysis method in this chapter, a consistent \(h\) value is set at the concrete-soil interface. This is because of the methodology of back-analysis. It solves the model with a series of boundary conditions and selects the result which matches the monitored data. If the \(h\) value change is considered, there could be a combination of different \(h\) values with countless possibilities, which is not applicable here. Therefore, at this first step the \(h\) value across the concrete-soil interface was kept consistent during the whole test period. The \(h\) value was adjusted from 1 to 6 (Wm\({}^{-2}\)K\({}^{-1}\)). Figures 9-12 show the temperature profiles at the positions of the VWSGs located in  
Figure 8: Model and mesh of the Shell Centre energy pile. the borehole, applying the conditions that \(h=3\), 4, 5, and 6 (Wm\({}^{-2}\)K\({}^{-1}\)). If the simulated curve is lower than the monitored one in the cooling mode circle or higher than the monitored one in the heating mode circle, this means the heat transfer was more efficient than the real situation. Therefore, the value of \(h\) was overestimated, and hence the value was reduced. Figure 9: \(Cont.\)  
Figure 9: Temperature profiles in the borehole when the heat transfer coefficient across the concrete–soil surface was 3 W/m\({}^{2}\) K.  
Figure 10: Cont. From the Figures 9-12, it can be seen that as the heat transfer coefficient rises, all the simulated curves exhibit the same trend of change. A large \(h\) applied at the concrete-soil interface can raise the peak temperature and pull down the valley. As expected, a larger value of \(h\) means that the heat flux is easily transferred to the ground; therefore, when the energy pile is working as a heat source/cold source, the nearby ground becomes hotter/colder. Figure 10: Temperature profiles in the borehole when the heat transfer coefficient across the concrete–soil surface was 4 W/m\({}^{2}\) K.  
Figure 11: Cont. According to the temperature profiles, the heat transfer coefficient value is complicated. It seems that the appropriate values are quite different from the different temperature values measured by the thermistors. For example, for VWSG1 the appropriate value of \(h\) is around 6 Wm\({}^{-2}\)K\({}^{-1}\), while for VWSG3 4 Wm\({}^{-2}\)K\({}^{-1}\) is already too large to fit the curves. Figure 11: Temperature profiles in the borehole when the heat transfer coefficient across the concrete–soil surface was 5 W/m\({}^{2}\) K.  
Figure 12: Cont. Table 3 lists the curve matching conditions for different \(h\) values at each VWSG. The symbol \"+\" means that the \(h\) value is overestimated, and \"+ +\" means that the peak (valley) of the simulated curve is more than 2 \({}^{\circ}\)C higher (lower) than the monitored one. The symbol \"-\" means that the \(h\) value is underestimated, and \"- -\" means that the peak (valley) of the simulated curve is more than 2 \({}^{\circ}\)C lower (higher) than the monitored one. The symbol \"O\" means that the \(h\) value can make the two curves fit each other. \begin{table}
\begin{tabular}{c c c c} \hline  & **Cooled** & **Heated** & \(h\) **(Wm\({}^{-2}\)K\({}^{-1}\))** \\ \hline \multirow{4}{*}{VWSG1 (1.5 m depth)} & - - & - & \(h=3\) \\ \cline{2-4}  & - & - & \(h=4\) \\ \cline{2-4}  & - & - & \(h=5\) \\ \cline{2-4}  & + & - & \(h=6\) \\ \hline \end{tabular}
\end{table} 
Table 3: Curve matching conditions for different \(h\) values at each VWSG. Figure 12: Temperature profiles in the borehole when the heat transfer coefficient across the concrete–soil surface was 6 W/m\({}^{2}\) K.  
From Table 3, it can be concluded:  
1. For VWSG 4 and 5, a consistent \(h\) value can be made to fit the whole curve.