Operating performance of middle-deep coaxial borehole heat exchangers based on TRNSYS simulation
Bibliographic record
Abstract
ABSTRACT Application of the middle-deep coaxial borehole heat exchanger (CBHE) in building heating has been gradually accepted by the public, and has become one of the emerging technologies to extract geothermal energy. This study aims to provide theoretical references for practical projects by simulating the long-term heat transfer characteristics of CBHEs using TRNSYS software. Firstly, this paper proposes a dual-mode operation strategy based on the dynamic response of thermal loads and constructs the middle-deep CBHE system model using software modules. After comparing inlet and outlet water temperature between data obtained from an actual project and the simulation results to validate the model, the impact of factors including the geothermal gradient, ground thermal conductivity, specific heat transfer rate, and run-time ratio are simulated. Additionally, the variation laws of system performance and the energy efficiency of thermal extraction under different influencing factors are analyzed. The results show that the outlet temperature decreases as the geothermal gradient decreases, and the CB^gHE system cannot operate normally for a long time when the outlet temperature is low. According to the influence of ground thermal conductivity on inlet and outlet water temperatures, insulation measures should be taken. To ensure long-term stability between ground heat extraction and heat recovery, the specific heat transfer rate of a continuously operating heating system should not exceed 150 W/m. Moreover, intermittent heating can improve the specific heat transfer rate of a single well. The system average coefficient of performance (COP) increases with the increase of the geothermal gradient and the ground thermal conductivity. When the specific heat transfer rate is 350 W/m, the run-time ratio increases from 1/3 to 5/12, and the energy efficiency of thermal extraction decreases from 16.6% to 11.22%.
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How this classification was reachedexpand
Full frame machine prediction
Teacher imitationNot calibrated prevalence, not ground truth. Human validation pending. The Gemma side is a direct model label for every work in the frame, read from the title-only record. The Codex side is a classifier learned from the 10,348 direct Codex labels and calibrated to design-weighted sample rates; fields without enough sample support carry no Codex call. Candidate is the union of the two sides; consensus is their intersection. These outputs are machine_predicted_unvalidated and are not human labels.
Distilled classifier scores by category (both heads)
| Category | Codex | Gemma |
|---|---|---|
| Metaresearch | 0.000 | 0.001 |
| Meta-epidemiology (narrow) | 0.001 | 0.000 |
| Meta-epidemiology (broad) | 0.000 | 0.001 |
| Bibliometrics | 0.000 | 0.000 |
| Science and technology studies | 0.000 | 0.000 |
| Scholarly communication | 0.001 | 0.000 |
| Open science | 0.001 | 0.000 |
| Research integrity | 0.001 | 0.000 |
| Insufficient payload (model declined to judge) | 0.002 | 0.000 |
Machine scores (provisional)
The two teacher heads of the student model, read on this work. A score orders the frame for review; it never asserts a category, and the validation status ships verbatim with every row.
Baseline scores from an immature model (maturity gate not passed, 7 training rounds). Scores rank; they never assert a category.
score_only:v0-immature-baseline · verbatim from the scoring run: score_only means the number may rank works, and no category label ships from itClassification
machine, unvalidatedMachine predicted; a candidate call from one source (direct Gemma or distilled Codex), not a consensus.
How this classification was reached, model by model and score by score, is at the end of the page under "How this classification was reached".