## 5 Conclusions  
In the present paper, a thermodynamic analysis is carried out for AdHT systems, focused on the investigation of several working pairs that can be suitable for low-temperature industrial waste heat vaporization. The investigation comprised 10 working pairs, using 4 working fluids, to represent a wide class of adsorbents that can be considered useful for the application. Different parameters were analyzed by evaluating thermodynamic efficiencies and specific energies of the AdHT. The main outcomes of the analysis are summarized below:  
* The implementation of an AdHT system using two separated adsorbent beds represents the most efficient solution, thanks to the possibility of implementing internal heat recovery between the operating phases. Furthermore, the double-adsorbers configuration allows the continuous provision of heat upgrading effect, thanks to the operation of the adsorbers in counter-phase. On the other hand, the specific energy that characterizes each working pair is only slightly affected by the AdHT architecture, thus representing a viable solution when a discontinuous process is expected, due to the much simpler architecture. * The effect of a temperature difference to be considered in each heat exchanger to guarantee a proper heat transfer was considered as well. Particularly, the comparison between ideal conditions and real conditions, in which 5 K of temperature difference between sinks/sources and components, were investigated. As expected, considering a real driving temperature in each circuit strongly affects the achievable performance, by lowering the achievable specific capacity and COP and thus reducing the operating conditions under which the AdHT can be effectively implemented. * Following the obtained results, the performance analysis of AdHT under different boundary conditions was performed for a double-adsorbers configuration and considering the reported temperature difference between external sinks/sources and the components. The investigated conditions considered a variable ambient temperature from \(-10\)\({}^{\circ}\)C up to 30 \({}^{\circ}\)C and two main applications, extremely low waste heat temperature, i.e., 40-50 \({}^{\circ}\)C, to be upgraded for DHN applications and waste heat temperature at 80 \({}^{\circ}\)C to be upgraded and re-used in the industrial process. The results confirm that, for both cases, the most promising adsorbent materials are the composites, in which a hygroscopic salt is embedded in a porous matrix, thus enhancing the achievable sorption capacity. This is valid both with methanol and water as working fluids. In particular, a composite based on MWCNT and LiCl, with methanol, looks to be the most efficient one for upgrading waste heat at 40-50 \({}^{\circ}\)C, able to provide a GTL of 20 K up to the ambient temperature of 10 \({}^{\circ}\)C with an appreciable efficiency (i.e., COP = 0.5)and specific energy (i.e., higher than 1000 kJ/kg). Differently, for the higher waste heat temperature of 80 \({}^{\circ}\)C, the most promising solution is represented by a composite using a silica gel and LiCl with water as working fluid. In this case, a GTL up to 50 K can be achieved, with a maximum ambient temperature of 20 \({}^{\circ}\)C, still guaranteeing high COP (i.e., 0.48) and specific energy (i.e., higher than 220 kJ/kg). These results demonstrate that, in general, to achieve a sufficient efficiency of the process, at least 40 to 50 K of temperature difference between waste heat source and ambient temperature should be available, thus confirming the fact that the AdHT technology is more suitable for industrial rather than residential applications. Furthermore, since the effect of temperature difference in each component is extremely relevant, careful design should be performed to maximize the achievable performance. This preliminary study can be considered as a useful tool for the selection of working pairs for AdHT systems development.