Conjugate Heat Transfer and <i>U</i> Value Analysis of 3D Concrete Printed Envelopes With Variable‐Thickness Air Cavities in Hot‐Arid Climates

ABSTRACT 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 m 2 structure. Results demonstrate that wide cavities (&gt; 25 mm) develop strong buoyancy‐driven circulation ( Ra ≈ 10¹¹ at Δ T = 20 K), severely degrading insulating performance and yielding high U values of 2.67–3.29 W/(m 2 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.