## 4 Simulation Results
### Comparison between One-Bed and Two-Beds Configurations  
In order to comparatively evaluate the different achievable performance of the Configuration I (one adsorbent bed) against the Configuration II (two adsorbent beds), the expected COP and specific energies were calculated. The selected working pair was the AQSOA Z02/water, while, for the sake of simplicity, the compared conditions were the ones exploiting ambient heat at 10 \({}^{\circ}\)C, both in the case of 40 \({}^{\circ}\)C and 80 \({}^{\circ}\)C of waste heat. In this case, \(\Delta\)T = 0 K, which stays for ideal heat transfer, was considered. Figure 4 summarizes  
\begin{table}
\begin{tabular}{c c c} \hline \hline
**Refrigerant** & **Adsorbent Material** & **Reference** \\ \hline Water & Silica gel Siogel & [26] \\ Water & AQSOA Z02 & [26; 27] \\ Water & MWCNT-LiCl & [28] \\ Water & SGST Silica gel-LiCl-35 & [29] \\ Ammonia & Activated Carbon SRD 1352/2 & [30] \\ Ammonia & Activated Carbon KOH & [30] \\ Ethanol & Activated Carbon SRD 1352/2 & [31] \\ Ethanol & Silica gel-LiBr & [31] \\ Methanol & Activated Carbon Carbotech A35/1 & [32] \\ Methanol & MWCNT-LiCl & [28] \\ \hline \hline \end{tabular}
\end{table}
Table 2: Investigated working pairs in the present work along with the reference from which the equilibrium data are taken.  
\begin{table}
\begin{tabular}{c c} \hline \hline
**Waste Heat Temperature [\({}^{\circ}\)C]** & **Ambient Heat Temperature [\({}^{\circ}\)C]** \\ \hline From 40 to 80 & From \(-\)10 to 30 \\ \hline \hline \end{tabular}
\end{table}
Table 3: Investigated operating conditions for the AdHT.  
the obtained results. The evolutions are plotted against the gross temperature lift, GTL, as defined before.  
As expected, when the GTL increases, both COP and specific energy decrease, since the exchanged refrigerant per kg of the adsorbent in each cycle is reduced. Comparing Configurations I and II, it is evident that the efficiency for the two adsorbent beds configuration is always higher than the one adsorbent bed configuration, since the former one allows to recover part of the sensible energy during the switching phase, thus reducing the energy requested to drive the process. Additionally, in this case, being the process considered ideal, the maximum achievable heat recovery is considered, which is obtained when the \(\Delta\)T between desorber and adsorber reaches 0 K. Differently, the curves for the specific energy obtained for the two configurations are almost overlapped, since the main benefit of Configuration II, from the thermodynamic point of view, lies in the reduction of the needed driving energy. Indeed, the increased waste heat temperature is associated with a higher COP for the same GTL or much higher GTL for the same COP. Same is valid for the specific energy upgraded. Both trends can be attributed to the much wider uptake difference (\(w_{1}-w_{2}\)) at the higher waste heat temperature. Considering the higher efficiency of Configuration II as well as the possibility of obtaining a quasi-continuous thermal energy production, this configuration will be considered in the following analysis. Nevertheless, it has to be pointed out that in some specific cases, like waste heat recovery from batch processes, the configuration with a single adsorbent bed can represent an attractive solution, thanks to the possibility of reducing the system complexity and thus the related capital expenditures (CAPEX).