# Heat Transfer Performance and Operation Scheme of the Deeply Buried Pipe Energy Pile Group
## 4 Results and Discussions
### Heat Transfer of DBP-EP Group in Different Operation Schemes
#### 4.3.3 Energy Efficiency Ratio  
Figure 16 shows the variation of EER values for each DBP-EP under continuous operational modes at 24 h, 168 h, and 720 h. The data presented in the figure illustrates that under continuous operational modes, the EER values (energy efficiency ratio) of each pile show a decreasing trend with the progression of the heat exchange operation. \begin{table}
\begin{tabular}{c c c c c c} \hline
**Intermittent** & **1\#** & **2\#** & **3\#** & **4\#** & **5\#** \\
**Condition** & & & & & \\ \hline n = \(\infty\) (Q/W) & 4145.50 & 4123.92 & 4147.41 & 4124.91 & 4100.55 \\ n = 5 (Q/W) & (\(\downarrow\)0.62\%) & (\(\downarrow\)0.51\%) & (\(\downarrow\)0.60\%) & (\(\downarrow\)0.51\%) & (\(\downarrow\)0.40\%) \\ n = 2 (Q/W) & 3474.04 & 3461.67 & 3475.53 & 3463.23 & 3449.75 \\  & (\(\downarrow\)16.20\%) & (\(\downarrow\)16.06\%) & (\(\downarrow\)16.20\%) & (\(\downarrow\)16.04\%) & (\(\downarrow\)15.87\%) \\ n = 1 (Q/W) & 2849.55 & 2840.92 & 2850.52 & 2842.67 & 2833.64 \\  & (\(\downarrow\)31.26\%) & (\(\downarrow\)31.11\%) & (\(\downarrow\)31.27\%) & (\(\downarrow\)31.09\%) & (\(\downarrow\)30.90\%) \\ n = 1/2 (Q/W) & 2562.22 & 2555.89 & 2562.69 & 2557.66 & 2551.54 \\  & (\(\downarrow\)38.19\%) & (\(\downarrow\)38.02\%) & (\(\downarrow\)38.20\%) & (\(\downarrow\)37.99\%) & (\(\downarrow\)37.78\%) \\ \hline  & **6\#** & **7\#** & **8\#** & **9\#** & **Total** \\ \hline n = \(\infty\) (Q/W) & 4123.83 & 4141.55 & 4123.53 & 4146.01 & 37,177.21 \\ n = 5 (Q/W) & 4108.07 & 417.24 & 4105.99 & 4121.68 & 36,986.41 \\  & (\(\downarrow\)0.38\%) & (\(\downarrow\)0.59\%) & (\(\downarrow\)0.43\%) & (\(\downarrow\)0.59\%) & (\(\downarrow\)0.51\%) \\ n = 2 (Q/W) & 3466.32 & 3471.75 & 3464.91 & 3474.68 & 31,201.88 \\  & (\(\downarrow\)15.94\%) & (\(\downarrow\)16.17\%) & (\(\downarrow\)15.97\%) & (\(\downarrow\)16.19\%) & (\(\downarrow\)16.07\%) \\ n = 1 (Q/W) & 2845.12 & 2847.78 & 2844.21 & 2849.82 & 25,604.23 \\  & (\(\downarrow\)31.01\%) & (\(\downarrow\)31.24\%) & (\(\downarrow\)31.02\%) & (\(\downarrow\)31.26\%) & (\(\downarrow\)31.13\%) \\ n = 1/2 (Q/W) & 2559.77 & 2560.67 & 2559.05 & 2562.34 & 23,031.83 \\  & (\(\downarrow\)37.93\%) & (\(\downarrow\)38.17\%) & (\(\downarrow\)37.94\%) & (\(\downarrow\)38.19\%) & (\(\downarrow\)38.05\%) \\ \hline \end{tabular}
\end{table} 
Table 2: Mean heat exchange rate of the pile group during a 30-day operational period. At different time points, the EER value of pile 5# is lower than the other piles, and this difference gradually increases with the heat exchange operation of the pile group. At 24 h, the disparity in EER values between pile 5# and pile 6# is 0.02, while at 720 h, this difference increases to 0.08. It can be observed that the longer the pile group operates continuously, the greater is the performance degradation, and the more significant is the negative impact regarding the thermal exchange efficiency of the inner piles. Table 3 shows the average EER values of pile 5# running for 30 days under intermittent operational mode and continuous operational mode. The EER values for Pile 5 under intermittent operational mode surpass those recorded under the continuous operational mode, and the values decrease with the increase of the intermittent ratio. This phenomenon occurs due to variations in rest durations within the intermittent operational mode of the heat pump system, wherein longer periods of rest correspond to reduced electrical energy consumption. With a smaller intermittent ratio n, the instantaneous thermal exchange  
Figure 16: EER changes of pile group at different time periods in continuous operational mode. Figure 15: Variation in heat exchange rates between the 5# pile foundation and deep well across diverse operational modes. The dashed line in the gray box indicates the result emphasizing that “when the intermittent ratio is n = 5, the setting of deep well can better enhance the heat dissipation effect of the heat carrier fluid in the heat exchange pipe system, so as to improve the heat transfer performance of pile foundation”.