Construction and demolition waste as thermal storage in modular solar air collectors

Solar air collectors reduce ventilation heating demand, yet storage solutions based on construction and demolition waste remain insufficiently documented. This study compares recycled brick and concrete plates as sensible thermal storage in two geometry-matched modular collectors monitored outdoors in Bucharest for 34 days. Material properties, temperatures, irradiance, airflow, pressure drop, particulate matter, TVOC-equivalent signals, useful heat, thermal efficiency, heating coverage, and environmental impacts were evaluated. Recycled brick and concrete showed densities of 1743 and 1820 kg·m−3 and thermal conductivities of 0.715 and 0.885 W·m−1·K−1, respectively. Outlet temperature rise was generally 3–5 ± 0.71 K. On 27 April, both collectors met hourly heating demand from 13:00 to 17:00, while concrete retained a stronger late-day contribution. No sustained outlet increase occurred for PM1, PM2.5, or PM10. The material-stage LCA yielded 1.75 kg CO₂-eq per collector. Recycled mineral plates therefore support low-temperature ventilation preheating. Brick responded faster, whereas concrete provided longer discharge persistence.