# Review of Dew Point Evaporative Cooling Technology for Air Conditioning Applications
## 4 Dew Point Evaporative Coolers Research
### System Applications
#### 4.4.2 Desiccant Systems  
One of the solutions which is considered as the most promising for moderate and humid climates are desiccant systems based on the combination of a desiccant unit (solid or liquid) and indirect evaporative cooler. The desiccant device dehumidifies the air, and an indirect evaporative air cooler cools the air to the appropriate temperature level without adding any moisture. The key performance indicator describing desiccant cooling systems is thermal COP (defined as an amount of cooling capacity obtained by the unit divided by required heating capacity). The heating source is crucial to create an environmentally friendly cooling system. In the case of a desiccant cooling system, the heat source is needed to regenerate the desiccant. In Figure 5, a desiccant cooling system equipped with a M-Cycle heat exchanger (DPIEC) and solar collectors as a heat source is presented. It needs to be mentioned that waste heat, geothermal energy, or heat captured by a heat pump may be utilized to regenerate the desiccant. The key performance indicator of the system which utilizes heat to regenerate the desiccant is thermal coefficient of performance (COP) and seasonal coefficient of performance (SCOP):  
\[\text{COP}_{th}=\frac{Q_{CC}}{N_{th}} \tag{4}\]  
\(Q_{CC}\)--system cooling capacity, kW  
\(N_{th}\)--thermal power consumed for regeneration the desiccant, kW  
\[\text{SCOP}=\frac{\int Q_{CC}dt}{\int N_{th}dt} \tag{5}\]  
Due to this fact, one of the major challenges for the desiccant--evaporative air-conditioning systems--is an ability to achieve high values of thermal COP. Higher thermal COP means higher application potential and lower operational costs. The problem with achieving high thermal COP is that it is often connected with creating very complicated systems (including multistage, a solar-assisted heating system, multiple heat recovery exchangers, cooling towers etc.). In the case of conventional desiccant cooling systems, the end-point air treatment is connected with airflow humidification in direct evaporative coolers. In the case of indirect evaporative heat exchangers, the same required parameters of the supply air can be reached, but, taking into account that air is cooled sensibly (without moisture content rising), a significantly lower air dehumidification is required in the desiccant wheel. It is the main premise to develop desiccant systems based on the M-Cycle indirect evaporative coolers [50]. In this paper, several recent publications that take into account the use of an intermediate evaporative exchanger in sorption systems are presented. For example, [PERSON] et al. [51] used computer software to perform numerical simulations of different solar desiccant cooling systems integrated with M-Cycle cooler and evaporative cooler. The results show that for considered climatic conditions (moderate and humid, hot and semi-humid and hot and humid), the solar desiccant cooling systems integrated with the M-Cycle show better cooling performance than the system equipped with the typical evaporative cooler. One of the solutions which is considered as most promising for moderate and humid climate are desiccant systems, based on the combination of a desiccant unit (solid or liquid) and an indirect evaporative air cooler (system reaches the average COP\({}_{th}\) = 0.728). Desiccant cooling systems in different configurations with an indirect evaporative air cooling have been investigated by many authors in the past. [PERSON] et al. [52] compared a solid desiccant dehumidifier integrated with a cross flow Maisotsenko cycle heat and mass exchanger (HMX) with a traditional desiccant air conditioning system integrated with a direct evaporative cooler under different operating conditions and the same process and return airflow rates. It was found out that for the same supply airflow and regenerative airflow parameters, the first system was approximately 60-65% more efficient than the second one. [PERSON] et al.