| Ground source heat pump system(GSHPs),a central air conditioning system that transfers heat to or from the ground,has become increasingly popular due to its environmental benefits.As a new type of GSHPs,the pile-foundation GSHP system has attracted a large number of researches to evaluate its performance and benefits in recent decades.Firstly,heat transfer models of pile-foundation heat exchanger and pile-foundation heat exchanger group were established in this thesis.The initial and boundary conditions as well as simulation working flow were determined for the models.Secondly,the heat transfer processes of pile-foundation heat exchanger were simulated in both cooling and heating modes.The thermal effect on concrete could be significantly revealed after 1h.Heat transfer flux per meter of the heat exchanger(Q)gradually decreased and eventually stabilized at around 99.83W/m in cooling mode and 87.26W/m in heating mode after one-month experiment.The thermal effect radii were 4.43 m and 3.36 m respectively.Compared with concrete,the thermal effect on soil was delayed and the delayed time would increase along with heat transfer.Next,the heat transfer processes of pile-foundation heat exchanger group in four different conditions were analyzed.After the pile-foundation GSHPs running for one year,the average soil temperature increased by 0.42 K in non-equilibrium condition and decreased by 0.16 K in equilibrium condition.After system running for ten years,the above data went up to 2.91 K and 0.61 K,respectively.Apparently,the balanced cooling and heating load will lead to safe and effective operation in the long term.Finally,three experimental studies on heat transfer processes of pile-foundation heat exchanger were carried out,and the experimental results were compared with the simulated data.The maximum relative error was 7.73%,and the maximum difference was 7.34%,which means the experimental results were in good agreement with the simulated data. |
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