Underground Heat Transfer Characteristics Of River Seepage Ground Source Heat Pump System In Cold Region

Ground-source heat pump system has a very broad prospect in China,its energy saving,high efficiency and environmental protection characteristics provide a guarantee for the development of green building.Harbin is located in the severe cold area,with abundant geothermal resources and fresh water resources.Combining the two resources,it is beneficial to develop the ground source heat pump system and improve the heat transfer performance of ground heat exchanger.Compared with the conventional water source heat pump and ground source heat pump,the ground heat exchanger buried in the river,can combine the advantages of two kinds of heat pump,and has higher stability and heat transfer effect,has great potential to be developed.In this paper,according to the river seepage condition and the underground heat transfer of the ground-coupled heat pump system,a sandbox seepage test rig was established.According to the theoretical heat transfer model of buried pipeline heat source and Darcy seepage law,the average seepage velocity is3.07?10^-5m/s,The 200W/220V electric heating rod was selected as the heat source,and the soil temperature field in the sand box was measured.The experimental results show that the water content of the soil is stratified under the condition of non-seepage,and the heat transfer effect of the soil is better at the measuring point with large water content.The soil temperature field of seepage condition is closely related to the seepage velocity and pressure in the sand box.The seepage velocity is faster and the heat transfer effect is better in the position of large pressure drop.Comparing the two conditions,the soil thermal conductivity of seepage condition is 39%higher than that of no seepage condition.Fluent software was used to simulate the changes of seepage pressure and seepage velocity in the sand box.Heat transfer experiment was carried out and the error was less than10%.Finally,according to the characteristics of building load and long-term operation of the subway station along the Yangtze River in Harbin,the buried pipe system is designed and simulated by TRNSYS software.The simulation results show that:the subway building load,the cumulative cooling load is 454897kW,the cumulative heating load is 337355kW,the calculated length of vertical buried pipe of ground source heat pump system is 13243m,the depth of shaft is 100m,and the number of shaft is 34.Compared with the condition without seepage flow,the length of buried pipe is saved by 3311m,and the number of vertical wells is reduced by 8.During the ten years of operation,the average soil temperature showed a downward trend,compared with the two conditions,the fluctuation of the peak value of seepage condition is smaller,and the trend of temperature decline is slower.The longer the operation time is,the more obvious the difference of ground temperature is.