Study On Energy Efficiency Of Deep Borehole Casing Type Buried Pipe Heat Exchanger And Ground Source Side Water System

The ground source heat pump system with deep borehole heat exchangers is an emerging application technology that indirectly utilizes deep geothermal energy.It shows advantages of high water temperature and protection of the underground water.Because the drilling depth can reach 2000m,the power of the circulating water pump on the ground source side is as high as 10-30kW,and the power of the circulating water pump on the ground source side accounts for about 5%-10%of the heat flow rate between soil and buried pipe.Therefore,it is of great significance to study the ground source side heat resistance of ground source heat pump system with deep borehole heat exchangers and the energy efficiency of the ground source side water system.In this paper,the structure of the deep borehole heat exchanger with casing-type pipes is analyzed and the calculation method of the resistance along the flow path is determined.The main factors affecting the resistance along the path are simulated,and some optimization methods for deep borehole heat exchanger with casing-type pipes are obtained.The optimization method of the resistance of the tube heat exchanger along the path is proposed,and the characteristic curve of the pipe network of the ground source heat pump system under the reference condition is calculated.The heat transfer model of the deep borehole heat exchanger with casing-type pipes considering the power consumption of the circulating water pump on the ground source side is established.The numerical calculation is carried out by using the finite difference method.The difference process is used in the process of calculation.Iterative and chasing methods are used to solve the problem,and the heat transfer model of the deep borehole heat exchanger is programmed by FORTRAN language.The simulation results show that the effect of heat transfer on the ground source side circulating water pump on the heat exchanger can not be neglected,and the main performance of the deep borehole heat exchanger is simulated.The effects of different influencing factors on the water temperature at the inlet and outlet of the heat exchanger were studied.Taking a 8000m~2 residential building in Harbin as an case project,the energy efficiency of the ground source side water system of the ground source heat pump system during the heating season is simulated,and the mathematical model of the ground source heat pump unit,constant flow rate and variable-flow circulating water pump are established.The energy efficiency of the ground source heat pump unit and the ground source side water system of the ground source heat pump system under the given conditions are simulated.The results show that the operation mode of the ground source side constant flow and variable flow rate has little effect on the operation energy consumption of the ground source heat pump unit,but it has a great influence on the operation energy consumption of the ground source side circulating water pump.In a heating season,the ground-source variable flow rate of the ground source side is about 23.93%higher than that of the ground-source side water system under constant flow operation,which indicates that the variable flow operation of the ground source side is beneficial to the efficient operation of the system.