# Comparative Study of Energy Savings for Various Control Strategies in the Tunnel Lighting System
## 4 Results
### Tunnel Length Impact on Energy Consumption  
To evaluate the impact of tunnel length on energy consumption for different lighting control strategies, electrical costs per day under different traffic intensities were estimated using 100-day data for each of the eleven tunnels. The relationships between daily electricity costs and tunnel lengths for different control strategies are shown in Figure 8. The fitting equations for daily electricity cost versus tunnel length for the LCL, TSCS, and DACS strategies are shown in Equations (1)-(3), respectively.  
\[E_{\text{EC\_LCL}}=696.0254+0.0984L \tag{1}\]  
\[E_{\text{EC\_TSCS}}=487.2178+0.0689L \tag{2}\]  
\[E_{\text{EC\_DACS}}=374.5777+0.0529L \tag{3}\]  
where \(E_{\text{EC\_LCL}}\), \(E_{\text{EC\_TSCS}}\), and \(E_{\text{EC\_DACS}}\) are the daily electricity cost of the lighting system for the LCL, TSCS, and DACS strategies, respectively (kWh). The coefficient of determination \(R^{2}\) is 0.9955, which means the reliability of the equation is acceptable.  
\begin{table}
\begin{tabular}{c c c} \hline \hline
**Lighting CS** & **Installation Costs/S** & **Tunnel Type** \\ \hline LCL & 24,003 + 41.78 ((\(L-315\) m) \(\times\) 2/9) + 1060 ceil (\(L/1000\) m) & Bamboo cutting tunnel \\  & 25,228 + 41.78 floor ((\(L-315\) m) \(\times\) 2/9) + 1060 ceil (\(L/1000\) m) & End-wall tunnel \\  & 36,321 + 41.78 floor ((\(L-315\) m) \(\times\) 2/9) + 2066 ceil (\(L/1000\) m) & Bamboo cutting tunnel \\  & 37,547 + 41.78 floor ((\(L-315\) m) \(\times\) 2/9) + 2066 ceil (\(L/1000\) m, & End-wall tunnel \\  & 38,178 + 41.78 floor ((\(L-315\) m) \(\times\) 2/9) + 2066 ceil (\(L/1000\) m) & Bamboo cutting tunnel \\  & 39,404 + 41.78 floor ((\(L-315\) m) \(\times\) 2/9) + 2066 ceil (\(L/1000\) m) & End-wall tunnel \\  & 39,220 + 41.78 floor ((\(L-315\) m) \(\times\) 2/9) + 558 ceil (\(L/150\) m) + 2066 ceil (\(L/1000\) m) & Bamboo cutting tunnel \\ ICS & 40,446 + 41.78 floor ((\(L-315\) m) \(\times\) 2/9) + 558 ceil (\(L/150\) m) + 2066 ceil (\(L/1000\) m) & End-wall tunnel \\ \hline \hline \end{tabular}
\end{table}
Table 7: Initial installation costs of tunnel lighting systems for various control strategies.  
Figure 8: Energy consumption versus tunnel length for the four control strategies.  
The relationship for daily electricity cost versus tunnel length for the ICS strategy had a better fitting equation using an exponential function, which is shown in Equation (4).  
\[E_{\text{EC\_ICS}}=259.96+211.49e^{-(\frac{100}{L}-0.03)/0.0405} \tag{4}\]  
where \(E_{\text{EC\_ICS}}\) is the daily electricity cost of the lighting system for the ICS strategy (kWh).  
The coefficient of determination \(R^{2}\) is 0.99682, which means the reliability of the fitting equation, is acceptable. The results demonstrate that daily consumption increases with tunnel length.  
Data in Figure 8 show that the daily electricity costs increase with tunnel length for all lighting control strategies. The results also show that the ICS tunnel lighting system's energy consumption is consistently lower compared to the other three control strategies. This indicates that the ICS control strategy has the most significant energy savings potential.