Impact of internal structural configuration of hollow bricks HCB-8 as a thermal metamaterial: Solid and air distribution effect under various operating parameters: A numerical parametric study

This study examines hollow brick geometry as a thermal metamaterial with shape-dependent insulation performance. Independently of normative constraints, it aims to examine the effect of internal geometry on the thermal behavior of 15 hollow bricks of different internal structures designed from the reference hollow clay brick with eight holes (HCB8), in order to select a configuration that offers the best thermal insulation performance under the conditions studied. Various operating parameters are taken into account, including outside temperature, thermal conductivity of the solid material, emissivity, and filling material. Three types of insulation (polyurethane foam [PUF], expanded polystyrene [EPS], and cardboard powder) are used as filling material inside the cavities of the bricks in order to compare their thermal behavior with air. The findings highlight that how the solid parts and air cavities are arranged inside the brick has a real impact on its thermal resistance. They also show that the performance of each configuration can shift depending on the operating parameters. Configurations with elongated cavities incorporating protuberances (D4 and D2) provide the best thermal insulation in most situations studied (outdoor temperature, emissivity, and thermal conductivity). The only exception is the case without radiation, where configuration with three elongated cavities without protuberances (C2) becomes the most effective. For filled bricks, configuration with three or four elongated cavities, delivers the best thermal performance for all three insulation materials tested (EPS, PUF, and cardboard powder). In contrast, configuration with four cavities arranged in a 2 × 2 pattern (B1), generally the least efficient, shows a noticeable improvement once an insulating material is added. These results highlight the importance of taking external conditions and material properties into account in thermal analysis, as they can significantly alter the performance order of geometries and guide the design of more sustainable building materials.