Structure and Control Optimization of the Buried Pipe Group Heat Exchanger With Vertical Inlet and Flat Outlet

doi:10.12096/j.2096-4528.pgt.22111

Abstract

Abstract:

Objectives In order to improve the utilization efficiency of shallow geothermal energy, it is urgent to optimize the structure and control of ground heat exchanger, which affects the performance of ground source heat pump system. Methods A model of the buried pipe group heat exchanger with vertical inlet and flat outlet was established. Based on heat exchange system performance, the optimal structure and operation control mode were explored. Results The heat transfer per unit area increases with the decreasing of transverse longitudinal ratio of the pipe group arrangement. The effect is small when the transverse longitudinal ratio exceeds 0.15. The smaller the heat exchanger spacing is, the higher the soil utilization rate is, but the greater the thermal short-circuit loss is. Compared with the double-row single-outlet type, the heat exchange per linear meter of the double-row double-outlet type buried pipe is increased by more than 7%. The fork arrangement is better when the load is larger. The average outlet temperature of optimization structure in the whole summer is decreased by 2.28 ℃, and the soil temperature around the heat exchanger is decreased by more than 1℃. In the actual operation process, the control mode of the flow rate changing with load should be given priority. Conclusions The research results can provide a theoretical basis for the design and manufacture of ground source heat pump heat exchanger.

Key words: ground source heat pump, underground pipe group, heat exchanger, thermal short circuit, control mode

CLC Number:

TK 11

Peifa MA, Jie ZHANG, Chunyu YU, Haohan WANG. Structure and Control Optimization of the Buried Pipe Group Heat Exchanger With Vertical Inlet and Flat Outlet[J]. Power Generation Technology, 2024, 45(3): 478-485.

Figures/Tables 17

Fig. 1 Heat exchanger with vertical inlet and flat outlet

Fig. 2 Structure of double-row double-outlet and double-row single-outlet

Fig. 3 Heat transfer performance of two structures

Fig. 4 Temperature distribution of two structures

Fig. 5 Orthogonal combination of different flow rates, heat exchanger spacings, and vertical tube spacings

Fig. 6 Heat transfer performance of different combined structures

Fig. 7 Thermal short-circuit loss coefficient of different heat exchanger spacings

Fig. 8 Heat transfer per unit area with different rows

Fig. 9 Thermal short-circuit loss coefficients with different width-to-length ratios

Fig. 10 Temperatures with different rows

Fig. 11 Comparison of heat transfer performance between forked row and in-line row

Fig. 12 Temperature of forked row and in-line row

Fig. 13 Outlet temperature of heat exchanger under different control modes

Tab. 1 Structural parameters before and after optimization

结构	流量/(L/s)	竖直管间距/m	换热器间距/m	多列单出类型	叉排/顺排	控制方式
初始结构	2.4	2	1.2	双列单出	顺排	定流速
结构1	1.2	1	1.2	双列双出	叉排	定流速
结构2	3.6	1	1.2	双列双出	叉排	定流速
结构3	随负荷变化	1	1.2	双列双出	叉排	定温差

Fig. 14 Outlet temperature of heat exchangers with different structures

Fig. 15 Excess soil temperature in different structural horizontal directions at the end of summer operation

Fig. 16 Soil temperature of different structures at the end of summer operation

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