# 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
#### 4.3.1 Continuous Heat Transfer Characteristics of Pile Group
The average heat exchange rates (sum) are less than those of the continuous operational mode when the intermittent ratio n is small, specifically 14,145.38 W, 11,572.98 W, 5975.33 W, and 190.80 W. The trend indicates a convergence of the mean rates of heat exchange of the pile group towards the continuous operational mode as the intermittent ratio (n) escalates. Moreover, the disparity in heat exchange performance between the two operational modes diminishes with higher values of the intermittent ratio (n). At an intermittent ratio of n = 5, the aggregate average heat exchange rate of the pile group closely approximates that of the continuous operational mode. Despite a heightened instantaneous heat exchange rate of the DBP-EP at lower intermittent ratios, the overall duration of the heat exchange operation for the pile is abbreviated, consequently yielding a substantial variance in the average heat exchange rate relative to the continuous operational mode. Therefore, in practical engineering, operating conditions should be selected reasonably according to the requirements. Figure 14: Temporal evolution of heat exchange rate in pile 5# during intermittent operational mode. Figure 13: Temporal variation in thermal exchange rate of pile groups under continuous operational regime. By analyzing the temperature differential between the entry and exportation at the base of the 5# pile, we computed the mean heat exchange rate of the DBP-EP, subsequently contrasting it with the average heat exchange rate of the entire pile, as illustrated in Figure 15. On contrasting the thermal exchange outcomes of pile 5# between intermittent ratio n = 5 and continuous operational modes, observably, the mean heat exchange rates of pile 5# under both operational modes exhibit a minimal discrepancy, with only a 16.38 W differential. The thermal exchange curve of the deep well exhibits a progressive incline as the intermittent ratio n rises, with the rate of escalation gradually tapering off. Under intermittent operation at n = 5, the heat exchange rate of the deep well deviates by merely 91.47 W from that observed during continuous operation. Comparing the average heat exchange rates of the pile base under different operational modes, it can be seen that when n = 5, the average heat exchange rate of the DBP-EP base is the highest, exceeding that of the continuous operational mode by 75.10 W. Therefore, when the intermittent ratio is n = 5, the mean heat exchange rate of the pile base is optimal, and this intermittent operational mode can more effectively harness the elevated thermal conductivity inherent in the concrete foundation of the pile. In conclusion, compared to continuous operational mode, the intermittent operational mode demonstrates effective reduction of the thermal accumulation inside the pile, thereby increasing the instantaneous heat exchange capacity in the course of the operational duration of the pile foundation. When the intermittent ratio is n = 5, the setting of the deep well can better enhance the heat dissipation effect of the thermal carrier fluid within the system of heat exchange pipe, thereby improving the heat exchange performance of the pile foundation. Henceforth, the installation of borehole heat exchangers (BHEs) at the base of the pile foundation serves a dual purpose: harnessing the thermal diffusivity of the concrete at the pile base and augmenting the long-term efficacy of heat exchange within the energy pile.