## 4 Simulation Results
### Comparison of the Different Working Pairs  
As already highlighted in Table 3, the waste heat source temperatures considered in this study ranged between 40 \({}^{\circ}\)C and 80 \({}^{\circ}\)C, thus representing temperature levels usually dumped into the ambient. In the following, the selected working pairs (see Table 2) were investigated considering two possible final applications, namely upgrading waste heat to be used as primary source for low-temperature district heating network (DHN) applications and upgrading waste heat to be re-used in the industrial process above 100 \({}^{\circ}\)C. For the  
Figure 5: Analysis of COP and specific energy evolutions as function of the GTL, varying the waste heat temperature, the ambient heat, and considering both \(\Delta\)T = 0 K (solid lines) and \(\Delta\)T = 5 K (dashed lines) in all the two-bed AdHT components. (**a**) COP with 40 \({}^{\circ}\)C of waste heat temperature; (**b**) COP with 80 \({}^{\circ}\)C of waste heat temperature; (**c**) specific energy with 40 \({}^{\circ}\)C of waste heat temperature; (**d**) specific energy with 80 \({}^{\circ}\)C of waste heat temperature. former application, waste heat sources ranging between 40 \({}^{\circ}\)C and 50 \({}^{\circ}\)C were considered, with the injection of 50-60 \({}^{\circ}\)C in the DHN as the target, according to the fourth-generation DHN temperature levels [33]. For the latter application, waste heat source at 80 \({}^{\circ}\)C was considered, in order to guarantee the provision of heat at temperatures above 100 \({}^{\circ}\)C, which can be efficiently exploited in several industrial processes (e.g., pasteurization, sterilization, concentration, drying, distillation etc.) [34]. Figure 6 report both thermal COP and specific energy achievable by the different working pairs in case of 40 \({}^{\circ}\)C waste heat source temperatures. In this case, a minimum of 10 K of GTL was considered. Furthermore, the COP and specific energy were calculated every 10 K of GTL. As represented in Figure 6, when the waste heat source is available at 40 \({}^{\circ}\)C, only 10 K of GTL can be provided by most of the investigated working pairs with an appreciable efficiency and energy density. Furthermore, it is possible to obtain the GTL only when the ambient temperature, at which the process heat is dumped, is equal or below 10 \({}^{\circ}\)C. This restricts the exploitability of this waste heat stream to winter period and in cold climates. Another option is represented by the availability of other ambient heat sinks, characterized by a stable and low temperature throughout the year (e.g., lakes, rivers, etc.). In particular, two main working pairs showed promising performance, namely SGST-LiCl/water and MWCNT-LiCl/methanol. The former is able to achieve quite high COP, higher than 0.45 at 5 and 10 \({}^{\circ}\)C ambient temperature (Figure 6a), with specific energy ranging from 200 kJ/kg to 400 kJ/kg. The latter can achieve extremely high specific energy (Figure 6b), around 1500 kJ/kg for ambient temperature below 0 \({}^{\circ}\)C and above 400 kJ/kg at ambient temperature of 5 \({}^{\circ}\)C.  
These evolutions are guaranteed by the favorable equilibrium conditions of the embedded salt, LiCl, under these operating conditions. Differently, most of the pure adsorbents cannot be considered suitable under these conditions, since the achievable COP and specific energy are too low, especially at ambient conditions above 0 \({}^{\circ}\)C. It has to be pointed out that the working pair MWCNT-LiCl/methanol can also efficiently provide 20 K of GTL when the ambient temperature is below 0 \({}^{\circ}\)C. Specifically, it can achieve 0.5 of COP both at \(-\)10 \({}^{\circ}\)C and 0 \({}^{\circ}\)C, with 1040 kJ/kg and 940 kJ/kg of specific energy, respectively.