Simulation And Optimization Analysis Of Soil Source Heat Pump Based On EnergyPlus

Ground source heat pump is an efficient,energy-saving and environmentally friendly airconditioning system that uses geothermal energy to cool and heat the target building.The ground source heat pump system has been widely used in China because it does not consume groundwater,has good heat transfer performance and saves land.The use of ground source heat pump has become an important way to deal with the global energy crisis,climate warming and the development of low carbon economy.The key technology of ground source heat pump unit design is underground heat exchanger,drilling backfill material and buried pipe circulation velocity are the key design factors.The backfill material with high thermal conductivity can reduce the thermal resistance in the heat exchange hole,and the depth of the underground heat exchange hole and the length of the heat exchange tube.The scientific and reasonable circulation velocity of the buried pipe can reduce the energy consumption of the pump,thereby reducing the initial investment and operation cost of the ground source heat pump.In this paper,using Energy Plus simulation software,taking Feicheng shopping mall as an example,the model of ground source heat pump system is established.By changing the design parameters of underground heat exchanger,including two key factors of borehole backfill material and buried pipe flow rate,it provides practical significance for the design of ground source heat pump.According to the results of simulation data,the following conclusions are obtained :（1）When the buried pipe flow rate is 0.3m/s,0.6m/s and 1.2m/s,the system runs stably for 15 days,the outlet temperature is stable at 301.6K,306.4K and 309.1K,the inlet and outlet temperature difference is stable at 9.3K,4K and 2.5K,and the heat transfer per unit well depth is stable at 51.9W/m,60W/m and 62W/m.The flow rate of buried pipe increased from 0.3 m/s to 0.6 m/s,the outlet temperature increased by 4.8 K,increased by 1.6 %,the temperature difference between inlet and outlet increased by 5.3 K,increased by 56.9 %,but the heat exchange per well depth increased by 8.1 W/m,increased by 15.6 %;but from0.6m/s to 1.2m/s,the outlet temperature only increased 2.7K,increased 0.88 %,the import and export temperature difference only increased 1.5K,increased 37.5 %,the heat exchange per well depth only increased 2W/m,increased 3.4 %,the heat exchange per well depth basically unchanged.The smaller the velocity of the buried pipe,the longer the heat transfer time of the fluid medium in the pipe,the more sufficient the heat transfer,and the higher the outlet temperature;with the increase of the buried pipe flow rate,the heat transfer decreases,and the temperature difference between the inlet and outlet of the circulating medium in the pipe decreases.The heat transfer of the underground heat exchanger increases with the increase of the buried pipe flow rate,and the difference decreases with the increase of the buried pipe flow rate.However,the greater the buried pipe flow rate is,the greater the pump energy consumption and pipe resistance will be,and the final lift will increase.（2）The backfill material is raw soil backfill material,bentonite-based backfill material and cement-based backfill material.After the stable operation of the system,the outlet temperature is stabilized at 308.4 K,306.2 K and 300.8 K,the temperature difference between import and export is stabilized at 2.2 K,4.3 K and 9.7 K,and the heat exchange per well depth is stabilized at 39.3 W/m,53.2 W/m and 62.6 W/m.The outlet temperature of underground heat exchanger with backfill material changed from original soil backfill material to bentonite backfill material decreased by 2.2 K,0.7 %,the temperature difference between inlet and outlet increased by 2.1 K,95.4 %,and the heat exchange capacity per unit well depth increased by 13.9 W/m,35.3 %;the outlet temperature of underground heat exchanger changed from bentonite-based backfill material to cement-based backfill material decreased by 5.4 K,decreased by 1.8 %,the temperature difference between inlet and outlet increased by 5.4 K,increased by 125.5 %,and the heat transfer per well depth increased by9.4 W/m,increased by 17.7 %.The higher the thermal conductivity of the backfill material,the higher the heat transfer efficiency of the underground heat exchanger and the surrounding rock and soil layer.The lower the outlet temperature of the buried pipe,the smaller the temperature difference between the inlet and outlet of the buried pipe,the longer the outlet temperature of the underground heat exchanger tends to be stable,the higher the heat transfer per unit well depth,and the shorter the stable time.（3）The drilling depth will also change under different drilling backfill materials.The higher the thermal conductivity of the drilling backfill material is,the higher the thermal conductivity is,and the smaller the drilling depth is.Under the premise of satisfying the heat exchange of the system design,the project cost of a single drilling and U-tube has changed greatly in the economic benefit : the cost of a single heat transfer hole of the bentonite-based backfill material is reduced by 30.0 % compared with the original soil backfill material,the cost of a single heat transfer hole of the cement-based backfill material is reduced by 43.3 %compared with the original soil backfill material,and the cost of a single heat transfer hole of the cement-based backfill material is reduced by 19.0 % compared with the bentonite-based backfill material.On the basis of comprehensive consideration of buried pipe flow rate and economic applicability evaluation of borehole backfill material,and the lowest initial investment of pipe and borehole,0.6 m / s buried pipe flow rate and cement-based backfill material are selected as the optimal buried pipe flow rate and backfill material design parameters of ground source heat pump in this project.