A sustainable bio-adsorbent for thermal energy storage for space heating applications

Thermal energy storage is an emerging technology that allows the storage of heat when it is available, which can be used later. One of the available technologies for thermal energy storage is the adsorption of moisture from air by adsorbents. Several adsorbents have been studied in the literature for this application, but there is a need for a sustainable adsorbent that can be eco-friendly, cost effective, and available for scale-up for commercialization of the technology. The current paper focused on the synthesis of a flax shives-based composite (equal weight percent of flax shives and salt hydrates) prepared by the impregnation method and its application in thermal energy storage. The composite showed durability, stability, and reasonable energy storage density with a very low cost per unit of energy. The structural characterization of the hybrid was performed by scanning electron microscopy (SEM)/energy-dispersive X-ray spectroscopy (EDX). The thermal energy storage density, as well as the charging/discharging characteristics were measured using a laboratory-scale thermal energy storage apparatus. The flax/CaCl₂/LiCl hybrid showed reasonable energy storage density at 74 kWh/m³ for 50% inlet relative humidity after regeneration at 120°C. Although the energy storage density was not high, the flax/CaCl₂ composite was found to be the most cost-effective material, as it showed the lowest cost per energy stored at 0.98 CAD/kWh at 50% relative humidity (RH) after regeneration at 120°C.