# Performance Analysis of the Multi-Stage Dew-Point Indirect Evaporative Air Cooler
## 4 Conclusions  
In this study, the structure of a multi-stage evaporative cooling unit based on a combined cross-flow and regenerative counter-flow unit was analyzed. The most beneficial configuration was established on the basis of its geometry and performance analysis using validated numerical models. Based on the analysis performed, the following operating parameters and DPIEC 1 were chosen to achieve the highest cooling capacity: the relative length of the cross-flow part \(X_{cross}\) equals 0.7, the working-to-primary air ratio in the regenerative and cross-flow part equals 0.1 and 0.5, respectively. To achieve a compromise between the highest possible cooling capacity and the lowest outlet air temperature, DPIEC 2 was proposed. For DPIEC 2, the relative length of the cross-flow part \(X_{cross}\) equals 0.4, and the working-to-primary air ratio in the regenerative and cross-flow part equals 0.3 and 0.5, respectively. To find the proposed coolers' functionality, their performance was compared to the typical regenerative dew-point evaporative cooler performance. Despite DPIEC 1's highest cooling capacity, it reaches higher temperatures than the regular regenerative unit, while DPIEC 2 reaches even lower outlet air temperatures and lower cooling capacity. \begin{table}
\begin{tabular}{c c c c c c c c} \hline \hline \multirow{2}{*}{**City**} & \multirow{2}{*}{\begin{tabular}{c} **Inlet Air** \\ **Temperature** \\ \end{tabular} } & \begin{tabular}{c} **Inlet Air Relative** \\ **Humidity/(Air** \\ **Humidity Ratio)** \\ \end{tabular} & \begin{tabular}{c} **Air Dew-Point** \\ **Temperature** \\ \end{tabular} & \begin{tabular}{c} **DPIEC 2** \\ **Outlet Air** \\ **Temperature** \\ \end{tabular} & \begin{tabular}{c} **Outlet Air** \\ **Temperature** \\ \end{tabular} & \
\begin{tabular}{c} **DPIEC 3** \\ **Outlet Air** \\ **Temperature** \\ \end{tabular} &
\begin{tabular}{c} **DPIEC 4** \\ **Effectiveness** \\ \end{tabular} \\ \hline - & \({}^{\circ}\)C & \%/(g/kg) & \({}^{\circ}\)C & \({}^{\circ}\)C & \% & \({}^{\circ}\)C & \% \\ Athens & 33.8 & 31/(10.3) & 14.4 & 17.9 & 82.0 & 18.8 & 77.3 \\ Beijing & 37.4 & 45/(18.5) & 23.6 & 24.7 & 92.0 & 25.2 & 88.4 \\ Denver & 33.0 & 25/(7.9) & 10.5 & 15.6 & 77.2 & 16.8 & 71.8 \\ Helsinki & 26.7 & 46/(10.2) & 14.1 & 16.8 & 78.6 & 17.6 & 72.2 \\ Izmir & 35.5 & 55/(20.4) & 25.1 & 25.9 & 92.3 & 26.2 & 89.0 \\ Madrid & 36.1 & 29/(11.0) & 15.4 & 18.8 & 83.6 & 19.71 & 79.2 \\ Prague & 27.7 & 42/(9.9) & 13.6 & 16.6 & 78.7 & 17.5 & 72.3 \\ Warsaw & 32.0 & 50/(15.1) & 20.3 & 21.8 & 87.2 & 22.3 & 82.9 \\ \hline \hline \end{tabular}
\end{table} 
Table 5: Performance of the dew-point indirect evaporative coolers analyzed for the selected cities. Hence, in the final analysis for various locations, DPIEC 2 and the regenerative cooler were compared by simulating their performance. In general, the proposed multi-stage cooler configuration provides lower outlet air temperatures for all average outdoor air parameters in selected locations in comparison to the regenerative unit. For locations with higher air humidity (i.e., Izmir; see Table 5--bold values), the differences between the achieved dew-point efficiencies of the devices are higher than for locations with air parameters indicating a dry climate (Denver; see Table 5--bold values). Conceptualization, A.P. and D.P. ; methodology, D.P. and K.S. ; software, D.P. and K.S. ; validation, A.P. and A.J. ; formal analysis, A.P. and A.J. ; investigation, A.J. and A.P. ; resources, K.S. ; writing--original draft preparation, A.P. and A.J. ; writing--review and editing, M.P. and A.S.; visualization, A.P. and A.J. ; supervision, D.P. and A.P. ; project administration, D.P. ; funding acquisition, D.P., M.P. and A.S. All authors have read and agreed to the published version of the manuscript.