Characterization of Salt Hydrates for Compact Seasonal Thermochemical Storage

Abstract

This paper describes the characterization of four salt hydrates as potential thermochemical material for compact seasonal heat storage in the built environment. First, magnesium sulfate was investigated in detail using TG-DSC apparatus. The results of this study revealed that magnesium sulfate is able to store almost 10 times more energy than water of the same volume. However, the material was unable to take up water (and release heat) under practical conditions. A new theoretical study identified three salt hydrates besides magnesium sulfate as promising materials for compact seasonal heat storage: aluminum sulfate, magnesium chloride and calcium chloride. These salt hydrates (including magnesium sulfate) were tested in a newly constructed experimental setup. Based on the observed temperature lift under practical conditions, it was found that magnesium chloride was the most promising material of the four tested salt hydrates. However, both calcium chloride and magnesium chloride tend to form a gel-like material due to melting or formation of a solution. This effect is undesired since it reduces the ability of the material to take up water again. Finally, it was observed that performing the hydration at low-pressure will improve the water vapor transport in comparison to atmospheric pressure hydration.

A review on the use of calcium chloride in applied thermal engineering

“…Pure calcium chloride has also been investigated as TCM at small scale (40 g of CaCl 2 $2.3H 2 O) [136,143,148]. Although the authors observed gel formation that prevents further water uptake, calcium chloride showed interesting performance compared to other salts (Fig.…”

“…Indeed, an agglomeration problem, which prevents further water uptake, is often encountered when pure calcium chloride is used as thermochemical material (TCM). This problem is due to a partial melting of calcium chloride during the charging step (dehydration) or a partial formation of a solution of the material during discharging (rehydration) [143,144]. The use of additional material, which helps stabilize the physical structure of the calcium chloride as TCM further decreases the energy storage density.…”

“…But in general, only a part of this potential is used, depending on the process boundary conditions (temperature and pressure). For instance, for storage applications above 100 C, only the reactions in the range between the CaCl 2 $2H 2 O and the anhydrous (CaCl 2 ) could be used [59,142,143]. Furthermore, most thermochemical storage studies do not intend to use pure calcium chloride due to the issue of material stability (phase change, swelling/shrinking ¼ loose of porosity, etc.).…”

Magnesium Sulfate/Polymer Composites for Seasonal, Thermochemical Energy Storage

“…The used conditions for hydration and dehydration are probably not realistic for application in residential buildings, because of the high relative humidity for hydration and high temperatures for dehydration. The temperature lift has not yet been measured but can be estimated to be too low for commercial application according to measurements by van Essen et al [15]. These problems are known for magnesium sulfate and might be addressed by the use of other salts such as magnesium chloride.…”

Properties of optically and thermally stimulated luminescence of novel storage phosphor materials: Doped and undoped CsCaCl₃ ceramics

“…In the OSL spectrum of the Cu-doped CsCaCl 3 , an intense peak at 345 nm is observed in addition to a peak at 430 nm. The peak at 345 nm is close to the PL shoulder at around 350 nm and can be attributed to Cu 16) and the CsCaCl 3 : Cu tablets were synthesized after drying the starting materials at 423 K. However, the dehydration might not be sufficient to remove water and OH ¹ ions, leading to the residual of OH ¹ ions that can perturb Cu + ions. To detect OSL with less noise, the emission wavelength of the activator should be significantly shorter than that of the stimulation light.…”