# Review of Dew Point Evaporative Cooling Technology for Air Conditioning Applications
## 4 Dew Point Evaporative Coolers Research
### System Applications  
#### 4.4.1 Hybrid Air Conditioning System  
Dew point evaporative coolers are tested and studied as components cooperating with air-conditioning units, rotor desiccants, or some different cooling devices. Those systems are called hybrid systems in the literature. In the case of DPIEC working with an air handling unit (AHU), it is located before the AHU (Figure 4). It allows the air to be cooled initially, hence the cooling capacity of the AHU may be limited.  
[PERSON] and [PERSON] [44] proposed a conventional refrigeration system cooperating with an indirect M-Cycle evaporative cooling system in different arrangements for an office building located in North Italy. On the basis of the dynamic simulations, the energy savings were found for the summer season. Proposed system arrangements were compared to a typical air conditioning system. Generally, the results show that one specific application of the M-cycle offers a 37.6% reduction in energy extracted by the refrigeration cycle. [PERSON] et al. [45] developed a dynamic model of a hybrid air conditioning system (regenerative evaporative cooler cooperating with direct expansion system) for a residential building situated in Beijing in China. The system dynamic energy performance was presented on the basis of building load simulation results. In this study, authors compared the proposed hybrid system with traditional direct expansion (DX) system performance. The results show that usage of regenerative evaporative cooling device allows saving energy by 38.2% and 29.7% comparing to DX. [PERSON] et al. [46] experimentally analyzed a hybrid air conditioning system operating in humid tropical operating conditions in a lab scale. They supplemented the experiment with mathematical models of evaporative cooler and cooling coil and analyzed its performance numerically using daily weather data. [PERSON] et al. [47] proposed a hybrid air conditioning system operating in moderate climate conditions. The air handling unit is equipped with a regenerative DPIEC which precools the ambient air. The year-round, hourly-stepped building energy simulations were carried-out using a prognostic tool of energy consumption. The novel dew point evaporative cooler application potential was established using the black-box model based on regression equations. The hybrid system operation was compared to the typical air handling unit equipped with a standard energy wheel for heat recovery.  
[PERSON] et al. [48] presented a hybrid air conditioning system which consists of an integrated hydronic radiative cooling (RC) panel and a cross-flow dew-point indirect evaporative cooler DPIEC. It is worth mentioning that DPIEC is equipped with a closed cycle water reclamation using an air-water harvesting (AWH) system. An extensive hour-long analysis of the system operation for the building was carried out using the TRYNSYS  
Figure 4: Hybrid system scheme.  
software and mathematical models of the main elements of the system. The proposed system was mainly compared to a typical compressor system, which showed a reduction in electricity consumption. [PERSON] et al. [49] proposed a hybrid multi-device system that uses a dew point evaporative cooler. A mathematical model was used to analyze the system operation in various climatic conditions in China.  
In summary, using evaporative exchangers as the elements cooperating with other cooling systems, allows to reduce energy consumption, but at the expense of enlarging the size of the air conditioning unit. Hybrid air conditioning systems, using DPIEC and vapor compression systems, are mostly considered as air conditioning systems for hot and humid, moderate, and hot and dry climatic conditions.