中深层套管式地埋管换热器热−经济性分析及应用

To obtain the law of the influence of design parameters on the thermo-economic of medium-deep coaxial borehole heat exchanger, firstly, a flow and heat transfer model of medium-deep coaxial borehole heat exchanger with soil regions and economic model of heating system were established. Secondly, the influence of physical parameters(thermal conductivity of backfill material, inner pipe, and outer pipe), structural parameters (buried depth, inner pipe diameter, outer pipe diameter) and operating parameters(inlet temperature, circulating flow rate) on heat extraction performance of heat exchanger was explored. Thirdly, the influence of key parameters of heating system(buried depth, circulating flow rate, and number of wells) on system economic benefit was analyzed. Finally, thermo-economic optimization was carried out for a non-interfered geothermal heating project in Xi'an. The results show that the most important factor affecting the heat extraction performance is the buried depth, and the secondary important factors are the inlet temperature and circulating flow rate. The thermal conductivity of inner pipe, outer pipe diameter, thermal conductivity of backfill material, inner pipe diameter and thermal conductivity of outer pipe have little influence on the thermal performance. For the physical parameters, increasing the thermal conductivity of the backfill material, decreasing the thermal conductivity of the inner pipe and increasing the thermal conductivity of the outer pipe can improve the heat extraction performance of the heat exchanger. For the structural parameters, increasing the buried depth, decreasing the inner pipe diameter and increasing the outer pipe diameter can improve the heat extraction performance. For operating parameters, decreasing inlet temperature and increasing circulating flow rate can improve the heat extraction performance. Considering the initial investment, operation cost and project income, the thermo-economy of the system is evaluated by the dynamic payback period. When the buried depth is 3 000 m and the circulating flow is 25 t/h, the dynamic payback period of the system is shortened to 3.7 a.