Energy Evaluation of an Innovative Passive Building Using a Red Clay, Limestone, and Lime Composite for Mediterranean Regions

Mediterranean housing is increasingly shifting from a heating- to a cooling- dominated regime, making thermal comfort and energy efficiency central design challenges. This study assesses a passive multi-story envelope based on a red clay–limestone–lime composite. Thermophysical properties (ρ = 1800 kg/m³, c = 950 J·kg–1·K–1, and λ ≈ 0.70 W·m–1·K–1) were implemented in COMSOL Multiphysics 6.2 to run 1-D transient heat-transfer simulations of a layered wall over representative 72 h summer and winter temperature sequences. Relative to a cement-based reference wall, the composite halves daily indoor temperature swings (peaks reduced from about ±3 °C to around ±1.5 °C), increases phase shift, and reduces HVAC energy required to maintain setpoints (25 °C in summer and 20 °C in winter). For a 0.20 m core, cooling energy over 72 h decreases by 54.9% (32.136 to 14.506 kWh) and heating energy by 48.0% (52.496 to 27.289 kWh); increasing thickness to 0.30 m yields reductions of up to 58.8% (cooling) and 47.0% (heating). A conductivity sweep indicates best performance for λ ≈ 0.60–0.70 W·m–1·K–1. These results demonstrate the potential of locally sourced mineral composites to support passive-building strategies and Near Zero Energy Building (NZEB) objectives in Mediterranean climates. By combining traditional resources (red clay, limestone, and lime) with modern passive design principles, the proposed wall system offers a practical pathway to improved thermal stability, reduced peak loads, and enhanced indoor comfort.