# Review of Dew Point Evaporative Cooling Technology for Air Conditioning Applications
## 4 Dew Point Evaporative Coolers Research
### Optimization the DPIEC  
There are two main categories of solving the optimization problems: single and multi-objective optimizations. The single-objective optimization (SOO) includes the minimization or maximization of one performance criterion, while multi-objective optimization (MOO) improves more than one performance criteria at the same time. General information about the studies reviewed are presented in Table 4. \begin{table}
\begin{tabular}{c c c c} \hline \hline
**Method** & **Optimized Results** & **Objective Functions** & **Reference** \\ \hline SCO & Water and air flow arrangement & wet-bulb efficiency, COP & [35] \\ \hline MOO & Operational and geometric characteristics & Life-cycle cost, annual water consumption, & \\  & of the cooler & annual COP & [36] \\ \hline MOO & Inlet air velocity and working to air ratio & Life-cycle cost, annual water consumption, & \\  & (geometry optimized in previous study) & annual COP & [37] \\ \hline MOO & Velocity in dry channels, channel length, & Entropy production number & [38] \\  & working to intake air ratio & Entropy production number & [38] \\ \hline MOO & Channel length, channel gap, inlet air & & \\  & velocity and return to intake air ratio (for & Specific area, COP & [39] \\  & diverse climatic conditions) & & \\ \hline SCO & Channel gap, cooler height, NTU & Wet-bulb efficiency, enlargement coefficient, & \\  & synthetic index & & \\ \hline MOO & Optimal channel length and working ratio & Dew point effectiveness, COP, cooling & [41] \\  & for different scenarios & capacity & \\ \hline MOO & Operating and design parameters & COP, wet-bulb efficiencies, the surface area & [42] \\ \hline SCO & Construction costs & Cooling efficiency & [43] \\ \hline \hline \end{tabular}
\end{table} 
Table 4: Counter-flow DPIEC optimization. SOO, single-objective optimization; MOO, multi-objective optimization; COP, coefficient of performance. [PERSON] et al. [41] proposed a robust optimization of DPIEC, considering its favorable dew point effectiveness, cooling capacity, and coefficient of performance (COP). The 2-D model was enriched with optimization algorithms. The model agrees with experimental tests performed using the fabricated prototype (made of polyethylene terephthalate). In working channels, the 200 \(\upmu\)m thick layer of wick material was used to absorb and retain water. Due to extruding the wick material from the wet channels and dipping into the water tank, the water can be spread into the wet channels via the capillary effect. In this study, the researchers found the optimal channel length and working ratio for different scenarios. [PERSON] et al. [35] also researched the optimized DPIEC in terms of water flow arrangement. They used experimental and numerical methods to analyze the exchanger. The results show that wet bulb efficiency and COP of DPIEC were 29.3% and 34.6% higher respectively. The exchanger was equipped with a high wettability porous fiber placed on corrugated plates of the wet channel. [PERSON] et al. [40] performed the optimization which allowed them to find the optimum channel gap, which is in the range between 2 mm and 3 mm and 3 mm and 4 mm under condensation and non-condensation states. They obtained the optimized NTU, which was 4-7 and 3-5 under condensation and non-condensation states respectively. [PERSON] et al. [7] developed a precise model of the dew-point indirect evaporative cooler. They carried out the optimization of the system by determining optimum values of channel length, channel gap, inlet air velocity, and return to intake air ratio for different cities. It allowed the average coefficient of performance to be maximized and the specific area of the cooler to be minimized simultaneously. Through this development, the system reached its full potential for diverse climatic conditions. [PERSON] et al. found entropy production as an optimization indicator, hence they proposed a numerical model that combined the law of energy conservation and the principle of irreversible thermodynamic theory.