Abstract
Informal housing in hot climates commonly uses corrugated galvanized iron (GI) sheet roofs, which absorb intense solar radiation and rapidly transmit heat indoors, causing thermal discomfort and elevated heat-stress risk. This study evaluates a low-cost, construction-ready retrofit: a 20° pitched ventilated double-tin roof with a continuous air cavity and distributed inlet–outlet vents to enhance buoyancy-driven heat removal.
A multi-scale modelling–measurement framework integrates peak-load CFD with conjugate heat transfer and radiative effects to resolve cavity airflow, transient EnergyPlus simulations using Typical Meteorological Year (TMY) data to predict diurnal indoor response, and validation using a 1:3 scale outdoor prototype under summer conditions in Pune, India.
Results show buoyancy-dominated ventilation within the cavity (Rayleigh number ≈ 1.3 × 105), forming a stable upward flow that removes absorbed heat before it reaches the indoor-facing sheet. Compared to a single-layer GI roof, the system reduces inward heat flux by 30–35% and lowers indoor operative temperature by up to 6.2°C (4–6°C average). Experiments confirm roof-surface temperature reductions of 14–17°C and enhanced indoor cooling (8–12°C) under wind-assisted conditions. An optimal cavity gap of 6–10 cm is identified.
The study provides experimentally validated design guidance for scalable, low-cost passive cooling in climate-vulnerable housing.
Practical application
This study provides construction-ready guidance for improving thermal comfort in buildings with corrugated GI roofs, commonly used in low-cost housing. The proposed ventilated double-skin roof system uses simple materials and passive airflow to reduce indoor heat gain without mechanical cooling. The identified optimal cavity gap (6–10 cm) and quantified performance improvements enable practitioners, engineers, and builders to implement an effective, low-cost retrofit strategy. The findings are directly applicable to building design and refurbishment in hot climates, particularly in resource-constrained settings where energy-efficient and affordable cooling solutions are required.
The thermal performance reported in this study corresponds to newly installed GI sheets. In practical applications, dust accumulation, surface weathering, and oxidation may gradually increase solar absorptivity over time, leading to higher outer-sheet temperatures and some reduction in cooling effectiveness. Nevertheless, the underlying buoyancy-driven ventilation mechanism remains active and may partially compensate for the increased solar heat gain through enhanced natural airflow within the cavity. Periodic cleaning or the use of reflective coatings could help maintain long-term thermal performance in dusty environments.
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