Simulation Study On Heat Transfer Performance And Temperature Field Of Ground Source Heat Pump Inclined Buried Pipe System

The ground source heat pump system is widely used in the field of building energy conservation because of its stable performance,environmental protection,high efficiency and energy saving.At present,horizontal and vertical laying methods are widely used for buried pipes at home and abroad.However,the horizontal laying method occupies too much land,and the vertical laying method is difficult to construct and requires high initial investment.In densely populated areas,because there is not a large enough area to install buried pipe group,the vertical pipe laying method is also limited.Compared with vertical drilling,the thermal interference between adjacent boreholes in inclined drilling is much smaller.In this case,inclined buried pipe is a favorable choice.At present,the laying angle and arrangement method of inclined buried pipe system in domestic and foreign literatures are still lacking,which affects the heat transfer effect of buried pipe.In this paper,the heat transfer enhancement of ground heat exchanger will be analyzed and discussed from two aspects: the simulation study of inclined ground heat exchanger arrangement and the experimental measurement of thermal diffusion coefficient of backfill material.In this paper,firstly,a three-dimensional heat transfer model of inclined single Ushaped ground heat exchanger is built,and the underground heat exchange process and soil temperature distribution of the inclined ground heat exchanger are simulated.The heat storage effects of different inclined ground heat exchangers are compared,and it is found that the heat diffusion rate of the ground heat exchanger is the slowest in the heat storage stage when the angle between the ground heat exchanger and the vertical direction is 15.Furthermore,through the superposition principle,the heat exchange process of radial ground-buried tube group is simulated,and the heat exchange effects of inclined ground-buried tube group with different number of groups and different ground-buried tube spacing are compared.It is considered that when 8 groups of inclined ground-buried tube heat exchangers are selected and the ground-buried tube spacing is 3m,the inclined ground-buried tube heat exchanger group can exchange more heat energy without causing too serious soil heat accumulation.In addition,different proportions of quartz sand,metal materials,new composite materials and fine sand were tested,and the thermal diffusion coefficient was measured.The results showed that the thermal diffusion coefficient of the composite materials was the highest when the mixing ratio of fine sand and quartz sand was 4:6,when the mixing ratio of quartz sand and metal was 4:1,when the mixing ratio of new composite materials and metal was 1:9,and when the mixing ratio of new composite materials and quartz sand was 1:3.Through orthogonal test,it is found that the new composite material has the greatest influence on the thermal diffusivity,followed by metal material and quartz sand.In this paper,by simulating and analyzing the heat transfer process of inclined buried pipes,the actual underground space distance between adjacent buried pipes is increased,the thermal interference between buried pipes is reduced,and the heat transfer between buried pipes and soil is enhanced.At the same time,by measuring the thermal diffusion coefficient of backfill materials with different proportions,the best proportion of backfill materials with the maximum thermal diffusion coefficient in the measurement range is obtained.It has certain reference value for the design and construction of ground heat exchanger and the design and operation of ground source heat pump ground heat exchanger system.