关键词: 地热能, 地源热泵, 岩土传热, 地埋管换热器, 岩土分层, 解析模型

Abstract: In order to better describe the thermal behavior of ground heat exchangers（GHE） in a layer stratum, a general analytical model is developed and the corresponding analytical solution is obtained using Green's function method; The Green's function, which is the temperature response of single instantaneous ring source, is obtained using the separation of variables technique. The proposed model considers layer stratum and anisotropic properties, and it is applicable for both borehole heat exchanger and pile foundation heat exchanger which are two types of GHEs mostly used in engineering application. Computational examples of the model in a double-layered stratum are presented. The results show that it is necessary to adopt the layered model when long-term temperature response of a GHE is considered, since the error of neglecting the inhomogeneous feature increases with increasing time. There is a critical zone, and the temperature response in this zone can be described by a homogenous model using thermal properties of the corresponding layer. The thermal conductivity of each layer has great effect on the temperature response of a GHE. The steady temperature of soil decreases markedly as the ratio of thermal conductivity between soil layers increases. The ratio of GHE length to diameter also affect the thermal behavior of a GHE, and the steady temperature increases with increasing ratio of GHE length to diameter. The effect of GHE length to diameter on the steady temperature is more pronounced when the thermal conductivity ratio is smaller.