Climate-Sensitive Energy Performance Assessment of Bio-Based Building Envelopes
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Bio-based construction materials are increasingly promoted as sustainable alternatives capable of reducing the environmental footprint of buildings while enhancing energy efficiency. However, many comparative studies assess these materials against conventional wall systems of equal thickness, often neglecting the influence of thermal mass and climate-specific behavior at the whole-building scale. Due to their lightweight structure and limited thermal mass, bio-based systems may struggle to balance heating and cooling demands across different climates. This study evaluates the energy performance of hemp concrete, wood concrete, and straw-based wall systems, emphasizing the interaction between insulation, thermal inertia, and climate conditions.
Methodological Framework and Co-Simulation Strategy
A validated co-simulation methodology integrating TRNSYS and MATLAB was employed to assess whole-building energy performance. Two analytical scenarios were developed to isolate and evaluate key thermal effects. The first scenario maintained equal thermal transmittance (U-value) across materials to specifically examine the role of thermal mass. The second scenario allowed variable wall thicknesses to investigate dynamic thermal behavior and its influence on annual heating and cooling loads. This dual-scenario approach enabled a comprehensive understanding of insulation–mass trade-offs under varying climatic conditions.
Performance Under Equal Thermal Transmittance
When bio-based systems were compared with conventional insulated concrete walls at matched U-values, they exhibited higher total energy demands, particularly in climates where thermal mass plays a crucial buffering role. In oceanic and Mediterranean climates, the absence of significant thermal inertia limited the capacity of bio-based envelopes to dampen indoor temperature fluctuations. For example, straw-based buildings showed substantial increases in total energy consumption compared to insulated concrete counterparts in Vichy and Tripoli, highlighting the sensitivity of lightweight systems to dynamic climatic variations.
Influence of Wall Thickness and Dynamic Thermal Behavior
Increasing wall thickness improved heating performance in bio-based buildings, reducing heating demand by approximately 35–70 kWh/m² depending on climate. However, this improvement came at the cost of increased cooling loads, which rose by 8–17 kWh/m² across all studied climates. These results reveal a fundamental trade-off: while added insulation reduces winter heat losses, it may also trap internal gains and elevate cooling requirements in warmer periods. The findings underscore the importance of climate-responsive envelope optimization when designing lightweight, high-insulation systems.
Material-Specific Climate Adaptability
Among the evaluated materials, wood concrete demonstrated comparatively better energy performance in hot climates due to its balanced insulation and moderate thermal inertia. Hemp concrete showed stronger performance in cold climates, where heating demand dominates and insulation effectiveness is prioritized. Straw-based systems, while offering strong insulation properties, displayed greater sensitivity to climatic variability and thermal mass limitations. These distinctions highlight the need for material selection strategies tailored to regional climatic conditions.
Design Implications and Adaptive Strategies
The study emphasizes that bio-based envelopes cannot be evaluated solely on steady-state thermal metrics such as U-value. Instead, dynamic performance, thermal mass contribution, and climate interaction must be considered holistically. Adaptive strategies—including optimized wall thickness, integration of passive cooling measures, shading systems, and hybrid envelope configurations—are essential to enhance the performance of bio-based buildings. By aligning material selection and design strategies with climate-specific requirements, bio-based construction can contribute effectively to sustainable and energy-efficient building practices.
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