Effect Of Groundwater Seepage On Heat Transfer And Soil Of Ground Source Heat Pump

With the large-scale promotion of ground source heat pump,some problems gradually appear,such as heat transfer efficiency decreased of ground heat exchanger and low energy efficiency ratio,and so on.One of the reasons for this phenomenon is that the soil temperature is not running under the design conditions.It makes the soil heat absorption and heat dissipation unbalanced and reduces the heat transfer efficiency of the ground heat exchanger.The running results of many engineering cases show that ground source heat pump can still run very well under the condition of hot and cold unbalance due to the presence of groundwater seepage.Moreover,the soil can be re-equilibrated under the combined action of thermal diffusion and groundwater seepage after several years(usually 2-4 years).Therefore,it is very important to determine the velocity and direction of groundwater seepage.Groundwater seepage was considered as a favorable factor in the comprehensive thermal conductivity of the soil calculated by the thermal response experiment in previous studies,but it was unreasonable.Thermal diffusion and thermal convection are two ways of heat transfer between the ground heat exchanger and the soil.Thermal diffusion is the heat transfer between the soil and the double U pipe.While thermal convection is a kind of heat transfer between groundwater seepage and double U pipes.They belong to two kinds of heat transfer mechanism,thus they should be considered separately.This paper aims to obtain the value of groundwater seepage velocity and direction,and the contents of this paper are as follows:(1)A method of estimating groundwater seepage velocity and direction by using improved thermal response experiment is proposed.In this method,a set of temperature monitoring device is added on the basis of the traditional geotechnical thermal response test device.And use the monitored data to calculate the velocity and direction of groundwater seepage.The temperature monitoring device includes two sets of temperature sensors,and they are located in aquifer(34 m)and the aquifer(26 m).Each set of temperature sensors contains eight temperature sensors,which are evenly distributed around the ground heat exchanger.Through the soil temperature field around them to measure the ground heat exchanger.(2)On the basis of the above methods,the thermal response experiment platform was constructed and the thermal response test was carried out.When the soil initial temperature test,the circulating water inlet and outlet temperature sensor is 18.9?,the temperature of the soil temperature sensor at 34 m is 18.6?,and the temperature at 26 m is 18.3?.(3)In the constant heat flow test phase,the temperature of the eight points at a certain time is fitted to obtain the direction of groundwater seepage at that moment.Similarly,all the data are fitted to obtain the local groundwater seepage direction for the west to the north 28.35°?east to the south 28.35°.(4)Gambit software is used to simulate the 3D heat exchanger of ground heat exchanger.The non-aquifer without groundwater seepage is set as a solid area,while the aquifer with groundwater seepage is set as a porous medium area.In addition,a set of groundwater seepage velocity is set up according to the actual groundwater seepage direction.The simulation results show that the groundwater seepage velocity is 38.9m/a in the area by comparing the simulation temperature value and the measured temperature value of the eight points in the aquifer by Fluent software.(5)Proposed a set of ground source heat pump design-check the system,and through the specific examples of engineering.