## 2 Materials and Methods  
Three alternative materials: crushed coconut shells (\(CS\)), crushed burnt clay hollow brick (\(BC\)) and pumice stone (\(PS\)), were selected as raw materials to manufacture evaporative cooling pads, according to their availability and low-cost in the subtropical country of Colombia. Their cooling efficiency was compared with the frequently used cellulose cooling pad (\(CL\), Munters Brasil Industria e Comercio Ltda, Araucaria, Brazil). Two particle range sizes of coconut shell: 7.93 to 12.7 mm (\(CS_{1}\)) and 12.7 to 19.0 mm (\(CS_{2}\)); one range size of burnt clay hollow bricks: 12.7 to 19.0 mm; and two range sizes of pumice stone: 34.9 to 45.0 mm (\(PS_{1}\)) and 45.0 to 55.5 mm (\(PS_{2}\)), were evaluated. For each material, a pad of 0.5 m of height by 0.5 m of width was manufactured. All the cooling pads had a thickness of 0.1 m (Figure 1). The thickness was selected from a balance between pressure drop and cooling efficiency from previous research [28]. The pads were tested in an instrumented wind tunnel [32], increasing the air inlet velocity (\(u\)) from 0.5 m s\({}^{-1}\) to 3.5 m s\({}^{-1}\) for the cellulose pad or with the pressure below 160 Pa or until test failure due to water force out of the pad. In addition, three water flows (\(Q\)) around the recommended value of 6.2 L min\({}^{-1}\) m\({}^{-1}\)[46] were tested: 2, 6.2 and 10 L min\({}^{-1}\) m\({}^{-1}\), to determine their incidence over the pressure drop across the pad. The mathematical model that described the fluid-dynamic and hygothermal behaviour of cooling pads, proposed by [PERSON] et al. [32], was used in order to compare the behaviour of the pads at different inlet air velocities (\(u\): 0.5 to 2 m\({}^{-1}\)), thickness of pad (\(L\): 0.05 to 0.15 m) and environmental conditions: dry-bulp temperature (\(T_{dh_{i}}\): 25 to 35 \({}^{\circ}\)C) and relative humidity (\(\phi_{i}\): 30 to 70%) of the inlet air. Twenty-one equidistant values from the inlet air relative humidity (\(\phi_{i}\)) interval and 11 values for each one of the other variables were selected, obtaining 307,461 combinations of different conditions to simulate for each pad. The cooling efficiency (\(\eta\), Equation (1) [46], where \(T_{dh_{i}}\) is the air temperature of the outlet air and \(T_{wb_{i}}\) is the wet-bulp temperature of the inlet air), the THI (Equation (2) [45,47]), the change in the dry-bulp temperature (\(\Delta T_{dh}\)) and relative humidity (\(\Delta\phi\)) across the pads were compared. For this purpose, it was required to quantify the specific surface area (\(\zeta\)) and the convective heat (\(h_{H}\)) and mass (\(h_{M}\)) transfer coefficients of each pad. \[\eta=\frac{T_{dh_{i}}-T_{dh_{o}}}{T_{dh_{i}}-T_{wb_{i}}} \tag{1}\]  
\[THI=0 ST_{dh_{o}}+\frac{\phi_{o}}{100}(T_{dh_{o}}-14.3)+46.3. \tag{2}\]  
A specific surface area of 372.6 m\({}^{-1}\) for the cellulose pad was considered [32]. For the other pads, it was estimated from the geometry of the particles. For the coconut shells and burn clay bricks, it was estimated from processing photographs of the particles, taking advantage of the fact that they present a planar geometry. The pumice stones were approximated to ellipsoids and the surface area was computed using the Knud Thomsen Formulae (A1) and the Dall Equation (A2) [48]. The results obtained with each expression were validated, covering the surface of each stone of a sample of 1000 g with one layer of aluminium foil. To determine the surface area of the aluminium foil, imaging processing was also employed. In Appendix A, the methodology followed is described in detail. The convective heat and mass transfer coefficients were compute using the correlation of Hilper, modified for cooling pads [13] (Equation (3)).