Dynamic Characteristics Of Soil Thermal Conductivity During The Operation Of The Soil Source Heat Pump

As a clean energy source,the geothermal source is inexhaustible and is highly respected in today's energy shortage.The soil source heat pump system is an efficient system that can convert low-grade electrical energy into high-grade thermal energy.The effective thermal conductivity of the soil is a direct expression of the soil's heat transfer capacity.In actual engineering,the effective thermal conductivity of the soil is usually set to an empirical value or a fixed value obtained through on-site thermal response tests to carry out the size design of the buried tube heat exchanger.However,during the operation of the soil source heat pump system,the temperature change characteristics of the soil around the buried pipe change,and the thermal conductivity will also change,which will adversely affect the soil heat transfer process.In particular,in the presence of groundwater seepage in the soil,the temperature change characteristics,seepage characteristics and physical property change characteristics shown are different,even if the same type of soil and different soil layers have different geothermal properties,and with the non-linear changes in the intermittent thermal storage / exothermic process of rock and soil,so simple constant setting cannot accurately describe its characteristics.In this paper,through the design and construction of a miniature soil source heat pump system experimental platform,a thermal probe device capable of measuring the dynamic change of soil thermal conductivity is developed,and the effect of various factors on the dynamic change of soil thermal conductivity during the operation of the soil source heat pump system is experimentally studied.And analyze the reaction of this effect on the underground heat transfer characteristics,and then provide a theoretical basis for the operation of the soil source heat pump system.Based on research problems and based on the similar heat transfer theory,the process of designing and building a miniature soil source heat pump experimental platform equivalent to a large-scale soil source heat pump system used in actual engineering was introduced.Considering the infiltration of the soil and the discharge of seepage water during the experiment,the soil tank is designed with a three-layer structure.At the same time,the design and calculation of the water pump,the temperature and humidity measurement and acquisition system of the experimental system were carried out in detail,and the uncertainty analysis of the experimental system was carried out.Based on this experimental system,we conducted an experimental study on the change of soil thermal conductivity during the operation of the soil source heat pump system under various conditions in winter and summer.Obtain the dynamic changes of soil temperature and soil thermal conductivity around the buried pipe under different operating conditions,the effects of the inlet water temperature of the buried pipe,the circulating water flow in the buried pipe,the system operation mode,and the soil moisture on the underground heat transfer characteristics and the soil thermal conductivity of the soil source heat pump system were analyzed.The results show that the thermal conductivity of the soil changes continuously with the operation of the system.The temperature of the soil around the buried pipe caused by the operation of the system changes,which causes the change of the thermal conductivity of the soil and is positively related to the temperature change.Every time the temperature increases or decreases at 1?,the thermal conductivity of the soil changes accordingly by 0.01 W /m·K,and the change in thermal conductivity reversely affects the change of the soil temperature field,which is a process of mutual coupling.Appropriate intervals help restore the temperature of the soil and continuously inject heat into the soil.