A novel composite-medium solution for pile geothermal heat exchangers with spiral coils.

This paper presents a new transient analytical model for describing the heat transfer process of pile geothermal heat exchangers with spiral coils (PGHE-SC). A numerical model has been established based on the finite element method to validate this new analytical model, which shows a good agreement between the two models. The temperature responses for different heat transfer conditions were calculated and are discussed. When the thermal conductivities of pile is twice as the one of soil, the dimensionless temperature at middle of the pile is 0.3832 which almost twice as the temperature response of homogeneous case. The results indicate that the thermal difference between pile and soil is an important factor influencing PGHE-SC simulation/design. As this new model not only successfully takes the limited length of an energy pile into consideration but also distinguishes thermal properties in its modeling process, it may provide a desirable and better design tool for the PGHE-CS. [ABSTRACT FROM AUTHOR]