Penalty‐Aware Numerical Assessment of a Surface‐Enhanced Internal‐Condenser HPHE With a Compact U‐Loop for Net Sensible Energy Recovery in Hot–Dry HVAC Applications

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ABSTRACT In hot–dry climates, ventilation‐driven sensible cooling demand remains a major barrier to energy‐efficient heating, ventilation, and air conditioning (HVAC) operation. This study numerically investigates a surface‐enhanced internal‐condenser heat‐pipe heat exchanger (HPHE) with a compact U‐loop for net sensible energy recovery in hot–dry HVAC applications. Three configurations were compared under identical operating conditions: a no‐loop baseline, a smooth U‐loop, and a spirally corrugated U‐loop with a thin copper coating. The smooth U‐loop was used to quantify the dominant gain associated with activating the internal heat‐recovery pathway, while the corrugated‐and‐coated configuration was used to assess the additional benefit of condenser surface enhancement. The main contribution is the penalty‐aware comparison of these configurations within a compact internal‐condenser U‐loop framework. A staged numerical framework was employed, combining porous‐media operating‐range screening, detailed three‐dimensional conjugate computational fluid dynamics, and supplementary transient volume of fluid (VOF) phase‐change assessment of the adopted 150 mm U‐loop; the adopted loop length was supported by a previously reported VOF‐based operability study. The results identified a favorable operating window at a face velocity of approximately 2.0–2.5 m s −1 . At the system level, recovered sensible heat increased from about 0.61 kW for the no‐loop baseline to approximately 2.00 kW for the smooth U‐loop and 3.04 kW for the corrugated‐and‐coated configuration. At the selected operating condition, the fan‐power penalty of the enhanced case remained below 20 W, yielding a net sensible recovery of approximately 3.02 kW. The corresponding hot‐side temperature effectiveness increased from about 17% to 79.5% and 81.0%, respectively. Grid Convergence Index values remained below about 2% for the selected grid‐sensitivity responses, and validation against published experimental data yielded recovered‐heat deviations of 4.7%–6.2% and outlet‐temperature deviations below 1%. Overall, the results demonstrate that the internal‐condenser U‐loop provides the dominant recovery gain, while condenser surface enhancement delivers an additional and practically favorable improvement when performance is judged using net sensible recovery rather than thermal gain alone.

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