## 3 AWG Evaluation Tools Short Review
The RR indicator has been expressed using various formulations, which can, sometimes, generate confusion. Nevertheless, the meaning of Equation (3) is clear enough, because it depicts the efficacy of the process in the atmospheric water extraction. For the same amount of extracted water, a higher RR means less air to be treated to achieve it. This tool is particularly useful for evaluating different solutions where the specific water content in the air is low and the possible system is required to maximise the extraction process. SEC measures the cooling energy required to produce one litre of condensed water under given environmental conditions. It is worth noting that, in many recent papers and real-world machine data sheets [28], SEC has taken the same definition as UPC and is used instead of the latter, as seen in [29; 34]. However, the UPC definition is more suitable for practical applications, as it accounts for all the energy required by the AWG to provide water, rather than just the portion used for the water condensation. In [33], the energy consumption of ancillary devices, such as inlet fans, is neglected, and SEC is employed in its original definition. Such an assumption may be acceptable if a few cubic meters of air are treated. However, when thousands of cubic meters per hour must be filtered and \begin{table}
\begin{tabular}{p{113.8 pt} p{113.8 pt} p{113.8 pt} p{113.8 pt}} \hline \hline
**Name and Reference** & **Expression** & **Measure Unit** & **Definition** & **Notes** \\ \hline Water Harvesting Rate (WHR) or Water Generation rate (WGR) [32; 33] & & & This indicator is generally used for commercial AWGs, it provides a metric for assessing the water production in terms of quantity. The higher the value, the greater the system yield. & This indicator is generally used for commercial AWGs, it provides a metric for assessing the water production in terms of quantity. The higher the value, the greater the system yield. & This indicator is a means to understand how much hysteresis has the adsorption–desorption cycle. In other words, it gives a measure of the percentage of the water that does not remain entrapped into the adsorbent material. It is addressed to AWGs based on desiccant materials. The higher the value, the less water entrapped in the desiccant. & This indicator is similar to WET, but it is focused only on the thermal energy required to obtain the desorption process. It is addressed to AWGs based on desiccant materials. The value, the less water entrapped in the desiccant. \\ \hline Water Harvesting Cycle thermal efficiency (\(\eta_{\text{WHT}}\)) [26] & & & The ratio between the water condensation energy, given by the multiplication of condensed water mass and specific condensation heat, and the thermal energy required by the adsorbent material to release the water (\(Q_{t}\)) & This indicator is similar to WET, but it is focused only on the thermal energy required to obtain the desorption process. It is addressed to AWGs based on desiccant materials. The higher the value, the better the thermal efficiency. \\ \hline \hline \end{tabular}
\end{table} 
Table 1: _Cont._moved through a heat exchanger, the energy consumption of fans may exceed 10% of the whole AWG energy consumption [21], making SEC, in its original definition, potentially misleading. Both SEC and UPC are expressed in kWh/L or kWh/kg, and lower values indicate better performances. SWP evaluates the space efficiency of AWG technologies. As previously mentioned, one of the most important issues in the atmospheric water capture field is achieving meaningful yields in a compact space. This is not only due to the limited availability of large areas but also because extensive systems can complicate maintenance and water treatment operations, increasing both complexity and costs. A higher SWP reflects greater system compactness. SMP is used to measure the effectiveness of the used material (and, indirectly, of the employed process) in water collection with desiccant materials. A higher SMP indicates that less adsorbent material is needed.