## 2 AWG Technologies
At any rate, this kind of material also requires a final air-cooling process in order to collect a meaningful part of water and to restore the material in its starting conditions. A promising approach consists of a mix between the desiccants oriented approach and the reverse cycle application, as the example described in ref. [33], where a thin layer of desiccant coats condenser coils. The condensation heat is used to extract humidity from the desiccant, while the absorption is performed on environmental air. The sorption-based atmospheric water harvesting is currently mostly focused on the development of new materials, but paying less attention to the entire system that should embed them thus with no clear calculation of the real energy cost [34]. Actually, complete machines based on such an approach are comparatively few and at an early stage of development [35]. Moreover, desiccant based technology very often is not employed in complete passive devices, but it only tries to minimise the energy required to obtain the vapour condensation. Normally, water harvesting machines are equipped with fans that need the external energy input. The main advantage of the desiccant material approach is the possibility to harvest water in dry climates, as desiccants are able to capture water at low humidities (under 30%), avoiding defrosting cycles. Nevertheless, in this case, large spaces are also required if more than a few L/day are needed. It is worth noting that one of the tests most performing reports a yield of about 5 L/(day m\({}^{2}\)) [10]. First rough attempts to make a comparison between a compressor-based solution and a desiccant based one, in water harvesting, were carried out in ref. [36]. However, in such a research, authors compared the behaviour of different types of dehumidifiers, instead of AWGs, as it was declared (and as it could be easily inferred by the quality of collected water). The results are not very meaningful for the AWG topic, as dehumidifier are not at all AWG machines, not from the point of view of employed materials, nor from that of the thermodynamic cycle set points design and control, and nor from the point of view of the quality of water, as underlined in ref. [37]. At any rate, when a considerable water harvesting is needed (exceeding few L/day), active technologies are required; thus, AWGs are affected by energy consumption that is related not only to the vapour condensation but also to the need to move the air inside the harvesting device, as said in ref. [37]. This last voice is very difficult to be avoided even if the condensation can be obtained by means of free cooling or other mechanisms, such as those employing new desiccant materials as that described in ref. [32]. When water production achieves the order of thousand litres a day, the energy consumption related to air moving can be very significant: several kWh a day [37]. Actually, the energy issue is one of the main concerns of the AWG technology. In particular, the energy consumption related to reverse cycle-based AWGs was estimated to be responsible for 50% of the entire cost of commercial water from air production [21]. One of the means to bypass such an energy issue is represented by AWG integrated machines, as said in ref. [23]. As described in ref. [38], an AWG integrated machine is a system able to extract water from air, by means of a compression reverse cycle, and, at the same time, to provide valuable side effects, coming from the water extraction process. The integrated machine can provide, with the same energy input (_en_), three useful effects:  
* a certain quantity of condensed water;
* a cooled and dried airflow that can be directly employed as primary air or convoyed into an Air Handling Unit (AHU) of an air conditioning system;
* a flux of heating energy, which can be used to heat up, for example, domestic water. A scheme of the process is reported in Figure 1, where it is possible to observe that the process is obtained applying a reverse cycle to the refrigerant and processing environmental air.