A composite cylindrical model and its application in analysis of thermal response and performance for energy pile

• A composite cylindrical model was developed which can be used in energy pile.
• The heat capacity of pile was considered in the model.
• The performance of some layout forms of heat exchangers in energy pile was analyzed.
• The model was applied to a TRT to estimate the thermal property parameters of soil.

Energy pile is a special vertical heat exchanger with the advantage of saving land area for buried pipe in recent years. Based on the composite line source model and cylindrical model, this paper presents a composite cylindrical model, and the heat capacity of pile in the borehole in ground source heat pump system (GSHP) was considered in the model. The model can be used in energy pile with a large diameter. It was validated by comparing to a 3-D numerical model which had been compared with a measured data set. The thermal performance of various layout forms of heat exchangers in energy pile was analyzed. In addition, the model was applied to a project of thermal response test (TRT) to estimate the thermal property parameters of soil. The simulation results showed that the composite cylindrical model have a better agreement from start of the test with measurement data. The model gives a new simulation tool in analysis of performance and TRT for energy pile.