Analysis On Heat Extraction And Storage Performance Of Different Types Of Buried Tube Heat Exchangers

In the era of renewable energy promotion,shallow geothermal energy systems have gained wide acceptance worldwide.Shallow geothermal energy is used for building heating and cooling,which meets the requirements of low carbon emissions and has great potential.Ground source heat pump technology is an important technology in the utilization of shallow geothermal energy.The focus and core of the research is the heat transfer characteristics of buried pipes.There are differences in the heat transfer performance of different types of buried pipes,and the total length of buried pipes is also different.This paper studies the heat transfer performance of single U-shaped buried pipe,double U-shaped buried pipe and multi-U-shaped buried pipe under the conditions of single heat extraction,single heat storage and annual operation;,water inlet velocity,thermal conductivity of backfill material,branch pipe spacing,seepage direction and seepage velocity,and other factors affect the heat extraction and storage characteristics of multi-U-shaped buried pipes;the drilling required for different types of buried pipes is calculated according to the dynamic load of the building.The depth and number of holes are given,and the temperature of the outlet water,the heat transfer of linear meters and the temperature rise of the soil under the operating conditions of the whole year are given.The specific research content of this paper is as follows:(1)Based on the general finite element software ANSYS,the calculation models of different types of buried tube heat exchangers were established,and the results of the geotechnical thermal response test were used to verify the models,and the measured values of the outlet water temperature of single U-shaped wells and double U-shaped wells were obtained The maximum relative error with the simulated value is 1.724% and 1.579%,respectively,and the maximum relative error between the measured value and the simulated value of the water inlet and outlet temperature difference is 5.31% and 5.62%,respectively,which verifies the accuracy of modeling using this software.(2)The outlet water temperature,the heat transfer capacity along the meter and the radius of influence of different types of buried pipes under the conditions of single heat extraction,single heat storage and annual operation were compared and analyzed.The heat exchange effect of the multi-U-shaped buried tube heat exchanger is better.Boreholes have a larger radius of influence.(3)Using Fluent to simulate the influence of different influencing factors on the heat transfer characteristics of multi-U-shaped buried pipes,it is found that the inlet water temperature has the most obvious effect on heat transfer.When seepage is not considered,there is a linear relationship between the outlet water temperature and the heat transfer heat in linear meters and the water inlet temperature of the buried pipe;when the water inlet speed is between 0.24-0.64m/s,the increase in heat transfer is more obvious When it is greater than 0.84m/s,the growth rate is small.The heat exchange capacity of the heat exchanger can be improved by adopting a lower(heat extraction)/higher(heat storage)inlet water temperature,appropriately increasing the inlet water flow rate,and increasing the distance between the branch pipes.(4)Using the control variable method,the heat transfer capacity of the buried pipe heat exchanger under different operating modes was simulated and analyzed.U-shaped buried pipe is better.Under this mode of continuous operation for 3 years,the maximum linear meter heat transfer of multi-U-shaped underground pipes has increased by about 60%,and the heat gain is significantly higher than that of the other two types of buried pipes.(5)Use Fluent to simulate the heat transfer under five different seepage velocities and three different seepage directions,and analyze the change of heat transfer with seepage velocity and direction.Under the heat extraction condition,the seepage velocity is from 0m/a to 200m/a,and for every increase of 50m/a,the relative increments of heat transfer in linear meters are:53.06%,18.83%,11.20%,and 8.08%;Under the following conditions,the seepage velocity ranges from 0m/a to 200m/a,and for every 50m/a increase in the seepage velocity,the relative increases in heat transfer along the meter are: 53.02%,18.86%,11.20%,and 8.07% respectively;the seepage direction and the X axis are The heat transfer heat transfer in the 45° direction is about 1.36 times that of the +X direction and +Y direction under the heat extraction condition,and about 1.22 times that of the +X direction and +Y direction under the heat storage condition,and even more when there is seepage Facilitate heat exchange between buried pipes.(6)Combined with the engineering project,use DEST software to calculate the dynamic load of the building,determine the load peak-shaving method,couple the dynamic simulation of the building and the water temperature of the buried pipe,and then obtain the number of wells required for different buried pipe forms,the temperature of the water in and out of the buried pipe,and the length of the meter.heat etc.Through research,it is found that the use of multiple U-shaped buried pipes can reduce the drilling configuration by half compared with single U-shaped buried pipes,which has a great advantage.