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.

118 approach supports energy saving and decarbonization through its simplicity, affordability, and scalability. Keywords: heat recovery, annular channel, porous filler, sand, heat exchanger, low-grade heat, regenerator, thermal storage, energy efficiency, ventilation. INTRODUCTION Low-grade heat (typically <180 °C) is widely present in industrial and municipal systems, yet it is most often irreversibly lost to the environment [1,2]. Estimates suggest that up to ~70% of generated energy is converted into low-temperature heat that is not reused for productive purposes [2]. Examples include warm exhaust air from building ventilation systems, flue gases from heating boilers, and waste air heat in industrial facilities. This energy dissipation represents a missed opportunity to improve energy efficiency and reduce the carbon footprint of enterprises [3]. Direct conversion of low-temperature heat into electricity is challenging due to low thermodynamic efficiency (as defined by the Carnot limit) when the temperature difference is small [3]. Therefore, increasing attention is being given to technologies for recovering this heat for heating and thermal applications, such as through heat exchangers (recuperators) and thermal energy storage systems. The practical importance of low-grade heat recovery is supported by the requirements of modern energy efficiency standards. In ventilation systems without heat recovery, up to 30–40% of heating energy may be lost. The use of heat recovery units allows a significant portion of this energy to be reclaimed: recuperative ventilation systems can return 50–80% of heat, and under optimal conditions—up to 90% [4]. Traditional gas boilers without economizers lose 10–20% of heat through flue gases; however, the installation of condensing economizers can reduce these losses by 5–15% [4]. Consequently, the issue of low-grade heat recovery is highly relevant from both economic and environmental perspectives, driving the search for new, effective solutions.