Conjugate Heat Transfer and U Value Analysis of 3D Concrete Printed Envelopes with Variable‐Thickness Air Cavities in Hot‐Arid Climates (2025-09)¶

The design freedom of three-dimensional (3D) concrete printing (3DCP) enables complex building envelopes with integrated air cavities; however, their thermal performance in extreme climates poses a critical challenge, particularly for cavities with nonuniform geometries. This study presents a combined experimental and numerical analysis of conjugate heat transfer in a real 3DCP building envelope featuring variable-thickness air cavities under hot-arid conditions. A comprehensive methodological framework was employed: (1) in situ U value measurements on north and slanted east cavity walls (3.75 m tall; max cavity width, 900 mm) with and without interior insulation, (2) development of a robust numerical model to simulate conjugate heat transfer across laminar to turbulent flow regimes, and (3) whole-building cooling load estimation for the 168 m2 structure. Results demonstrate that wide cavities (> 25 mm) develop strong buoyancy-driven circulation (Ra ≈ 10¹¹ at ΔT = 20 K), severely degrading insulating performance and yielding high U values of 2.67–3.29 W/(m2 K) for uninsulated walls—approximately 30% higher cooling loads than standard construction. Crucially, parametric analysis reveals that filling cavities with low-conductivity porous media (e.g., sand and k = 0.27 W/[m K]) effectively suppresses convection, restoring thermal performance to near pure conduction levels and reducing U values by up to 82% when complemented with insulation. These findings provide essential, practical strategies for optimizing energy efficiency in future 3DCP buildings constructed in hot-arid climates.