Performance assessment of open thermochemical energy storage system for seasonal space heating in highly humid environment

Open thermochemical energy storage (TCES) systems compactly store heat as chemical energy and are appropriate as seasonal heat storage for space heating. Often salt hydrates are employed as the solid reactants in open TCES, which undergo reversible reactions with water vapour present in the ambient air. Depending on the ambient air conditions, the salt may agglomerate or deliquesce, affecting the system's performance. In this work, thermogravimetry (TGA), X-ray diffractometry (XRD), and scanning electron microscopy (SEM) techniques are used to characterize the strontium bromide salt. Subsequently, the dehydration and hydration of the reactive salt (SrBr2.6H2O) are investigated experimentally under high humidity conditions in a laboratory-scale setup of open TCES located in Mumbai, India. During dehydration, high ambient humidity causes deliquescence at the beginning, resulting in agglomeration as the salt dries during the process. Consequently, a low global conversion of 0.15 and a charging efficiency of 3.5 ± 0.2% are achieved. During hydration, the dehydrated salt completely hydrates. Nevertheless, the salt deliquesces under high ambient humidity, resulting in increased heat capacity of the reactive bed and the formation of salt lumps. Consequently, a decreased local hydration rate is achieved. The reactive bed provides a maximum temperature lift of 2.1 K to the airflow and discharging efficiency of 35 ± 2%. The results obtained from numerical simulations performed using the transient model of the reactive bed show good qualitative agreement with the experimental results.