Experimental and Numerical Investigations on Thermal Interference of the Helix Ground Heat Exchanger for Ground Source Heat Pump System

Abstract

This study conducted an investigation on the heat transfer process of helix ground heat exchanger (HGHE) by numerical simulation and experiment. The concept of thermal interference index was proposed, and the thermal interference index in the soil around HGHE was investigated under different soil type conditions. The results showed that with the progress of the heat transfer process of the HGHE, the thermal interference of the soil around the HGHE gradually increases. Therefore, the transient heat transfer coefficient and efficiency coefficient of the HGHE decrease, which weakens the heat exchange between the HGHE and the soil to a certain extent. When burying the HGHE, priority should be given to the soil type with excellent thermal conductivity, which is conducive to the outward diffusion of heat emission from the heat exchanger. In this way, it can effectively reduce the thermal interference index of the soil around the HGHE and can indirectly improve the heat transfer performance of the heat exchanger. For example, in sandy loam soil type condition, the thermal interference at the middle of the busbar position is 2.14 (m·°C)/W, which is 83.3% of the clay loam soil type condition. Therefore, the heat flux of HGHE under sandy loam condition is about 20.7% higher than that under clay loam condition.