## 3 Results and Discussion
Maximum cooling power throughout the day corresponds to 645 W, and is reached using the highest number of desorber modules (with the dimensions specified in Table 1) and a mass flow rate through each channel of 4 mg/s. Figure 3:0 Desorption rate increase with respect to only using the base fluid. Daily solar coefficient of performance (SCOP) of the whole solar cooling facility, defined as the ratio between total cooling power and total incident solar radiation on the tilted surface, is represented in Figure 3:1 SCOP reaches a maximum of 14% using the maximum number of desorber modules, which corresponds to the minimum flow rate considered through the channels, as shown in Figure 3:2 In the same figure, the total cooling effect produced over the day is shown, reaching a maximum of 2.3 kWh for the same number of modules. Figure 3:3 Relation between the number of desorber modules and the daily SCOP and cooling effect produced using H\({}_{2}\)O-LiBr-CNT nanofluid. \begin{table}
\begin{tabular}{c c} \hline \hline
**Mass Flow Rate through the Channels (mg/s)** & **Number of Desorber Modules (with Data of Table 1)** \\ \hline
4 & 588 \\
8 & 294 \\
16.1 & 147 \\
40.2 & 58.8 \\
112.5 & 21 \\
643.1 & 3.7 \\ \hline \hline \end{tabular}
\end{table} 
Table 5: Characteristics of the desorber modules. Figure 7: Cooling power throughout the day using different mass flow rates through the channels. Figure 9 shows the relative increase in the cooling effect produced when CNT nanoparticles are added to the mixture. The increase is calculated with respect to the case of only using the H\({}_{2}\)O-LiBr solution. The best improvement represents a relative increase in the cooling effect of 6%. Benefits from adding nanoparticles decrease as the number of modules increases, owing to the better performance obtained in the membrane-based desorber when the mass flow rate decreases, irrespective of using nanoparticles. In addition to this, a higher number of modules increases the total cost of the absorption chiller. For this reason, a thermo-economic analysis should be performed to identify the optimum number of desorber modules. An exact economic analysis currently cannot be performed because the proposed system is under development and its real cost is unknown. As reference data, the sell price to our research group of a first experimental prototype manufactured ad hoc by a Spanish company was 7893.75 euros. This prototype had 50 hot water channels. A second prototype, including a few changes in the design, was sold for 2631.25 euros. This implies that huge reductions in the sell price can be obtained when large amounts of membrane-based desorbers are manufactured. In the following, an optimization process of the hot water channels number is performed. First, the chiller is supposed to sell the cold produced at the same cost of using a mechanical compression system. The electricity price for domestic use is 0.1349 \(\copyright\)/kWh [52]. The system is supposed to operate during the summer season (90 days) and for 25 years with an average COP of 2.5. The cost of a reversible compression chiller of 800 W cooling capacity is 559 euros [53]. It is considered that it is used for heating in the winter season, so only one half of its cost is taken into account. The cost of the solar collector is 383.57 euros [54], and it is supposed that it is used for hot water supply or heating for the rest of the year, so only one fourth of its cost is computed. The cost of the condenser, evaporator, and auxiliary components of the absorption chiller is supposed to be 100 euros. Finally, the cost of the desorber and absorber modules is supposed to be similar, and four hypothetical values are considered for the first module produced: 5, 15, 25, and 35 euros.