## 4 Comparison with Other Storage Materials  
As shown in [31], several classes of materials are available which can fit the requirements for heat storage applications. Table 3 reports the thermo-physical properties of sorbents suitable for application in thermal energy storage systems and compares them with the measured data for Z60.  
In particular, thermal conductivity for Z60 sample was experimentally measured by means of C-Therm TGi, a specific tool that allows the evaluation of the thermal conductivity and the effusiveness of the materials (solids, liquids, powders and slurries) using the technique defined \"Modified Transient Plane Source (MTPS)\", compliant with the ASTM D7984 standard.  
The other data presented are, instead, taken from literature while the ones on heat of adsorption are based on the experimental measurements.  
It is worth noticing that Z60 possesses enhanced properties for application in devices for heat storage, however the identification of the best material for heat storage is extremely application-related.  
Figure 8: Adsorption capacity of pure Z60 zeolite foams expanded in free space (open cylinder) and inside paperboard at different temperatures.  
\begin{table}
\begin{tabular}{c c c c c c c c} \hline \hline  & **Silica Gels** & **Zeolites** & **AIPOs/SAPOs** & **Composites** & **MOFs** & **Activated** & **Z60** \\ \hline
**Adsorption heat (kJ/kg)** & 160/180 * & 50/300 * & 250/300 * & 50/250 * & 20/200 ** & 45/900 *** & 375/450 * \\
**Typical desorption** & 50/80 & 70/350 & 60/90 & 60/90 & 60/150 & 80/200 & 60/80 \\
**temperatures** (C) & 650/700 & 650/900 & 800/900 & 300/600 & 1000/2000 & 700/750 & 780/1030 \\
**Density (kg/m)** & 650/700 & 650/900 & 800/900 & 300/600 & 1000/2000 & 700/750 & 780/1030 \\
**Specific heat** & 0.8/0.9 & 0.85/0.95 & 0.85/0.95 & 0.95/1.05 & 0.8/1.2 & 0.8/1.5 & 0.8/1.5 \\
**(kJ/kg *C)** & 0.15/0.2 & 0.15/0.25 & 0.15/0.25 & 0.15/0.30 & 0.10/015 & 0.15/0.75 & 0.15/0.25 \\
**Pressible refrigerants** & water & water & water & water, methanol, methanol, methanol, ethanol & water \\
**Amount of uptake** & & & & ethanol & ethanol & ammonia & water \\
**exchanged in a typical** & 0.030/1.0 & up to 0.2 & up to 0.25 & up to 0.8 & 0.16/0.40 & 015/0.60 & up to 0.25 \\ cycle (kg/kg) & & & & & & & \\ \hline \hline \end{tabular}  
* The heat of adsorption is calculated for a cycle with \(T_{ds}=100\) *C, \(T_{cmd}=30\) *C, \(T_{ds}=50\) *C, \(T_{cr}=10\) *C, with water as sorbate. ** The heat of adsorption is calculated from isotherms at 298 K, 303 K and 333 K, with water as sorbate.  
*** The range of heat of adsorption is calculated with methanol and ammonia as sorbate.  
\end{table}
Table 3: Comparison of Z60 properties with sorbent material classes for heat storage.  
Indeed, the operating conditions under which the material is employed can strongly influence its overall performance.  
As showed in the sections above, Z60 can be effectively regenerated at lower temperatures, significantly below 100 \({}^{\circ}\)C still having a higher uptake under the typical boundary conditions of thermal energy storage.  
Table 3 also shows as newly developed materials, such as MOFs and composites, exhibit also good properties for heat storage applications, however such classes of materials are still expensive or not commercially available. Classical materials (silica-gels, activated carbons, and zeolites), instead, are cheap and easily available, but present the worst performances.