Analysis Of Cold Accumulation Of Ground Source Heat Pump Wells With Different Tube Spacing In Severe Cold Area

Ground source heat pump technology is a kind of environmental protection and energy saving technology,which is a renewable energy.Nowadays,the practical engineering is widely used,and the geological condition has great influence on the operation of ground source heat pump.Changchun is a very cold area,and ground source heat pump systems take more heat out of the soil in winter than in summer,which results in a drop in underground soil temperature,with the time running,the soil temperature will decrease year by year,and the decrease of soil temperature will directly affect the efficiency of the ground source heat pump system.The buried pipe spacing is a direct factor that affects the operation efficiency of the unit.A suitable buried pipe spacing is very important to the operation and initial investment of the unit.In order to study the variation of underground soil temperature,this paper takes Yifu building of a university in Changchun as the research object,and studies the variation of soil temperature under different pipe spacing and different years of operation.To master the distribution of the underground soil temperature field has certain reference significance for the design of the ground source heat pump system.Some thermal properties of the soil,such as initial temperature of soil,specific heat capacity of soil,density of soil and comprehensive heat transfer coefficient,were obtained.This is very necessary for the simulation work.The actual model is established by Gambit,and the well groups of 4,5 and 6 meters interval are established respectively.In this paper,16 tube wells are used instead of ground source heat pump wells.In order to see the change of soil temperature around the wells,6 meters were taken from the outer edge of the three models,and the sizes of the three models were 24x24,27x27 and 30x30 respectively(in m).Then thesimulation software fluent is used to simulate the soil at 40 meters underground,and the ground source heat pump monitoring system is used to verify the reliability of the model.The results show that the soil temperature at the center of the buried pipe decreases by 0.18 °C in the first year and 0.54 °C in the second year In the first year,the soil temperature at the center of buried pipe decreased by 0.14 °C,and in the second year,the soil temperature at the center of buried pipe decreased by 0.33 °C The soil restoration degree in spring is higher than that in autumn whether it is 4meters or 5 meters apart.After the spring restoration,the lowest soil temperature of 4meters apart appears in the center of the well group,the lowest soil temperature of5 M interval wells is around the middle four buried pipes,but not in the center of the wells.The degree of cold accumulation of 5M interval wells is less than that of 4M interval wells,in the periphery of the well group,the soil temperature increased slightly.Within the buried pipe area,the temperature difference between 4 m and 5 m interval wells is 0.1 °c at the end of the first year.At the end of the second year,the temperature in the inner zone of the buried pipes of the 4-meter interval wells is decreasing obviously.After running for two years,there is no thermal interference between the buried pipes and the maximum temperature drop is 0.19 °C.After five years,the soil temperature at the center of 4-meter interval wells decreased by0.88 °C,and that at the center of 5-meter interval wells decreased by 0.65 °C.