Experimental Study On Soil Heat And Moisture Transfer At Source Side Of Ground Source Heat Pump Based On Refrigeration Conditions

With the increasing demand for heating and air conditioning of various buildings,the proportion of building energy consumption in the total energy consumption is increasing.Therefore it’s important and urgent to reduce building energy consumption.Ground source heat pump(GSHP)is widely used as a green and efficient air conditioning system.The most prominent process affecting the actual operating efficiency of the ground source heat pump system is the contact heat transfer between the buried pipe and the soil.In fact,moist soils occupy a considerable proportion of the strata.The heat transfer process between buried pipe and wet soil is carried out under the coupling action of heat and humidity.Therefore,it is significant and necessary to research the law of heat and moisture transfer of soil for the efficiency and energy saving of ground source heat pump.Loess and sand are widely distributed in northwest China.Therefore,this paper takes loess and sand as the research objects.Firstly,the thermal conductivity of loess and sand under different water content is measured by using the transient hot wire method,and the measurement results are compared and the reasons are analyzed.The influence of moisture content,measurement method and saturation on thermal conductivity was investigated.The relationship between saturation and thermal conductivity is well fitted.In order to further research the influencing factors and rules of heat transfer of buried pipes in wet soil,a one-dimensional soil heat and moisture transfer model box was built to carry out experimental analysis.By placing temperature and humidity measurement points at different locations from the heat source,the variation rule of temperature and humidity field in soil was studied when the temperature of heat source was 40℃,50℃,60℃and 70℃,the initial moisture content of loess was 0.3%,10%,19% and 28%,and the initial moisture content of sand was0.3%,10% and 19%,respectively.At the same time,the loess temperature and humidity recovery tests under different initial moisture content and different heat source temperatures were also carried out.The loess with initial moisture content of 19% and 28% was also tested for temperature and humidity changes under intermittent heating conditions.By studying the variation law of soil column temperature field in the heat transfer process,it can be concluded that the temperature rise range of each measuring point is positively correlated with the temperature of the heat source,and the temperature rise rate is negatively correlated with the moisture content of the soil column,and the higher the moisture content is,the higher the temperature of the measuring point will be after the heat transfer is stabilized.The temperature distribution of loess and sand under different heat source temperatures can be predicted by fitting the temperature of each measuring point after heat transfer stabilization of loess and sand,and quadratic fitting of the relevant parameters with the temperature of heat source.Through the study on the variation law of soil column moisture content in the heat transfer process,it was found that the moisture content at each measuring point increased firstly and then decreased.Taking the heat source temperature of 70℃ as an example,the loess moisture content increased from 19%,and the moisture content at measuring point 1 increased from 19% to 20.54%,then gradually decreased to 18.33%.The closer the measuring point is to the heat source,the higher the peak value of moisture content will be,and the lower the final moisture content will be after wet migration.Through the intermittent heating test,it was found that the soil moisture content decreased gradually after the temperature of the heat source was turned off,and the decreasing degree was positively proportional to the temperature of the heat source.The peak value of moisture content will decrease gradually with the increase of heating times,and the stable value of moisture content will also decrease gradually.By comparing the heat and moisture transfer rules between loess and sand,it is found that the temperature rise rate and heat and moisture transfer range of sand are stronger than that of loess under the same water content.The research in this paper provides theoretical basis and experimental reference for the optimization of GSHP layout and the development of intermittent operation efficiency,which has important practical significance for the application of GSHP in practical engineering.