Abstract
Energy piles serve both load-bearing and heat exchange functions, holding significant value in ground-source heat pump applications. However, under layered foundation conditions, the heat transfer mechanism of pile-soil heat exchange is rather complex. Existing analysis methods are mostly based on constant heat source models, and such simplified assumptions cannot effectively reflect the influence of dynamic heat power variations on the thermal response of energy piles. Therefore, improving the accuracy of this dynamic response has become a key issue in current research. To this end, a dynamic response calculation model for U-tube energy pile-soil heat exchange under non-constant heat source conditions in layered foundations is proposed, based on finite layer heat conduction theory and step heat flux theory. This model takes the inlet temperature of the U-tube as input conditions, and by combining a piecewise superposition method for temperature influence effects, equivalently treats the pile-soil heat exchange process as a time-varying heat source, thereby establishing a non-constant heat flux model. Based on the principle of energy conservation, the along-path temperature of the heat exchange medium within the U-tube and the distribution of variable heat source intensity under different time steps are solved. Furthermore, using the along-path variable heat source intensity of the U-tube as input conditions and combining it with the finite layer heat conduction calculation method for layered foundations, the time-varying characteristics of the foundation temperature field are solved, thereby effectively simulating the response process of energy pile-soil heat exchange under dynamic heat power variations. Research results demonstrate that the proposed model not only avoids the high time consumption issues of complex numerical calculations but also exhibits high computational efficiency, and can accurately characterize the temperature response variations of energy piles under non-constant heat flux conditions. This model provides a reliable theoretical basis and an efficient computational tool for engineering design, system optimization, and operational analysis.
Full Text
Preamble
Title: The Dynamic Response Analysis Method of Heat Conduction of U-shaped Buried Pipe Energy Pile in Layered Foundation under Unsteady Heat Source
Authors: Gang Jiang¹, Chenfeng Zong¹,²,³, Ziyi Wang¹, Qinhu Wang³, Haofan Yang¹
Affiliations:
¹ School of Transportation Science and Engineering, Nanjing Tech University, Nanjing 211816, China
² School of Civil Engineering, Nantong Institute of Technology, Nantong 226002, China
³ China Construction Installation Group Co., Ltd.
Abstract
Energy piles integrating structural load-bearing and heat exchange functions hold significant value in ground-source heat pump applications. However, the heat transfer mechanism governing pile-soil exchange in layered foundations is complex, and existing analytical methods predominantly rely on constant heat source models. This simplifying assumption fails to adequately capture the impact of dynamic thermal power variations on energy pile thermal response. Consequently, enhancing the accuracy of dynamic response predictions represents a critical research challenge.
To address this challenge, a dynamic response calculation model is proposed for heat exchange between U-shaped buried pipe energy piles and soil in layered foundations under unsteady heat source conditions, based on finite layer heat conduction theory and step heat flux theory. Using the inlet temperature of the U-shaped buried pipe as input, and employing a piecewise superposition method for temperature influence effects, the pile-soil heat exchange process is equivalently transformed into a time-varying heat source, thereby establishing an unsteady heat flux model. Based on the principle of energy conservation, the model solves for the temperature distribution along the heat exchange medium within the U-shaped pipe and the distribution of variable heat source intensity at different time steps.
Furthermore, using the variable heat source intensity along the U-shaped pipe as input and combining it with the finite layer heat conduction calculation method for layered foundations, the model solves for the time-varying characteristics of the foundation temperature field. This effectively simulates the response process of energy pile-soil heat exchange under dynamic thermal power variations. Research results demonstrate that the proposed model not only avoids the high computational cost associated with complex numerical simulations but also achieves high computational efficiency while accurately characterizing the temperature response variations of energy piles under unsteady heat flux conditions.
This model provides a reliable theoretical basis and an efficient computational tool for engineering design, system optimization, and operational analysis.
Keywords: Energy piles; Unsteady heat source; Layered foundation; U-shaped buried pipe; Dynamic thermal response