In order to study the influencing factors for the operation of the medium-deep geothermal buried pipe （MDGBP）, this work analyzed the long-term operation results of the heating system using the MDGBP in Xixian new area. A heat transfer model was established based on the geological data of Guanzhong Area and the depth was 2510 m. The simulation was used to study the influencing factors of operation condition, pipe structure and material of buried pipe. The results show that the average powers of No.1 and No.2 buried pipe in Xixian new area are both more than 310 kW, indicating that they have excellent heat supply capacity. The water temperature at pipe inlet changes obviously with the seasons, which can cause the fluctuation of the heat load and the water temperature of heat pump. In terms of structure, when inner diameter changes from 63 mm to 125 mm, the average water temperature at pipe outlet and heat transfer power decreases by 1.9% and 4.8%, respectively. However, it is not safe if the inner diameter is too small. Considering the safety and the influence of heat transfer, the optimal inner pipe should be ϕ110 × 10 mm; when the outer pipe diameter changes from 168.3 mm to 244.5 mm, the average water temperature at pipe outlet and heat transfer power increases by 3.5% and 9%, respectively. Considering the cost and the influence of heat transfer, the optimal outer pipe should be ϕ 177.8 × 19 mm. In terms of operation conditions, the water temperature at pipe outlet decreases with the increase of flow rate, and the heat transfer power had an opposite trend. With the increase of the inlet water temperature, the outlet water temperature increases and the heat exchange power decreased. In terms of material, the outlet water temperature and heat transfer power increases with the decrease of thermal conductivity of inner pipe and with the increase of the thermal conductivity of cementing material. Considering the change of heat transfer power and cost factors, the inner pipe is recommended in industry with thermal conductivity of 0.42 W/（m·K） and cementing material with thermal conductivity of 3 W/（m·K）.
Key words
geothermal energy /
buried pipes /
numerical simulation /
heat transfer performance
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