Proceedings of the International scientific and practical conference ―Science, technology and art in global context (July 8-10, 2025) / OP website: www.naukainfo.com. – Dresden, Germany, 2025. - 140 p.

122 • Chemical inertness and safety. Sand (SiO₂) is non-toxic, non-corrosive, and stable at atmospheric pressure. Unlike liquid carriers, it poses no leakage or combustion hazards and simplifies system design. Other materials—such as gravel, ceramic beads, or metallurgical slag—may also be used. While sand has low thermal conductivity (0.2–0.7 W/m·K) [8], mixing and convection help distribute heat effectively. Metallic foams offer better conductivity but are costly and less temperature-resistant. Moistening the bed can improve conductivity but is rarely used in gas systems. – Aerodynamic resistance : fine beds increase pressure loss, requiring stronger fans. Radial-flow geometries help reduce this, as shown in KTH‘s dual-layer pebble system, which halved losses [10]. – Particle containment : protective meshes are needed to prevent erosion or loss at high flow rates. – Contamination : soot and dust can clog pores; regular cleaning may be needed. – Structural load : with densities up to 1.8 t/m³, installations must account for weight and support. Despite these factors, sand offers a simple, affordable, and effective solution. ―Sand battery‖ concepts are gaining traction, with lab tests achieving up to 90% heat retention when well insulated [10]. The next section reviews practical applications of such systems. APPLICATION EXAMPLES IN VENTILATION AND HEATING SYSTEMS 1. Building Ventilation Systems Heat recovery from exhaust air in supply/exhaust units reduces heating demand. Instead of plate-type recuperators, a static regenerator filled with sand can be used. Two sand-filled channels operate alternately: one accumulates heat from exhaust air, while the other releases it to the incoming air—flow is switched by valves. This