Study on freezing characteristics of soil around ground heat exchangers of ground-source heat pumps based on apparent heat capacity method

In order to search the effect of soil freezing on heat exchange characteristics of ground heat exchangers in cold zone, develops a heat transfer model of soil around ground heat exchangers taking soil freezing into consideration, and solves the freezing phase change problem by apparent heat capacity method. Based on the numerical solution of the model, discusses the influences of the water content in soil, soil initial temperature, soil thermal diffusivity and Stefan number on soil temperature distribution and freezing velocity. The results indicate that the soil temperature is higher compared with unfreezing conditions and thus the heat transfer resistance is smaller, which contributes to the decrease of design length of the buried coil and system initial cost. It also proves that the increase of water content in soil is favorable to the design and operation of ground-source heat pumps. Moreover, the decrease of soil thermal diffusivity and Stefan number can stay effectively the soil freezing velocity.