## 2 Desiccant Air-Cooling-Based Evaporative Cooler System  
Conventional DPC systems are very efficient in operation in dry climates, but cooling efficiency drops significantly when operating in humid climates. However, the disadvantages of traditional DPC systems such as the use of extra water, lack of independent humidity and temperature control, and the great influence of operating conditions on cooling performance can be overcome with new cooling system designs. The high cooling performance of pre-cooled desiccant air cooling systems has been proven by [PERSON] et al. [18], whose cooling performance was investigated under different conditions. The performances of these systems, which were selected to implement a control strategy due to their high performance, have been further increased by the additionally developed independent temperature and relative humidity control strategy. This air cooling system consists of two DPC systems, one for pre-cooling and the other for post-cooling, and a unit with a desiccant wheel and heater for extra dehumidification. The general scheme of the controlled process is given in detail in Figure 1. The cooling system in the figure uses a cross-flow dew-point indirect evaporative cooler (DPIEC) as the pre-cooler and the counter-flow DPIEC as the post-cooler. The air taken from the atmosphere with the F1 fan is first cooled by entering the pre-cooler DPC (DPIEC-1). After this stage, if needed, this air is subjected to an extra dehumidification process via the desiccant wheel (DW). How much moisture will be removed from this air depends on the operation of the desiccant wheel cooling system. The air used in the desiccant wheel for the dehumidification process is taken from the atmosphere with the F3 fan, conditioned by the heater, and given back to the atmosphere. Meanwhile, moisture is removed from the actual air by the heat and mass transfer between the air passing through the desiccant wheel and the cooled air.  
The rotation speed of the desiccant wheel has been accepted as the main effective parameter of the amount of moisture removed, and it is aimed to control the dehumidification with the control of the motor that rotates the desiccant wheel. Then, the dehumidified air enters the post-cooler DPC (DPIEC-2) where the second cooling process takes place, where it is further cooled and given to the room. The air in the room is discharged to the outside and thus the air circulation of the process is completed by the F2 fan. It is assumed that all fans (F1, F2, and F3) are assumed to be the same and work in the same operating modes for the continuity of air circulation in the whole cooling system. In addition, there is a water pump (WP) for supplying cooling water to the DPIECs. For this water pump, which provides a low and constant flow water supply during the normal cooling performance of the system, an extra \"cleaning\" mode has been added in order to periodically clean the channels of the heat exchangers in the DPCs.  
As seen in the figure, there are sensors that measure the temperature (T), and relative humidity (RH) values of the room, the cooler, and the atmosphere. The data received from these sensors and the set values entered by the user are evaluated in the controller, and control inputs are generated for the actuators (F1, F2, F3, DW, WP) in the cooler. With these control inputs, the actuators are operated at different speeds throughout the process depending on the ambient conditions, and both the room comfort is provided faster and less energy is consumed. As can be seen in the figure, in addition to the temperature and relative humidity sensors, a flow rate sensor (FR) is used to measure the flow of the cooling water fed to the DPCs, and an energy meter (E) is used to measure the energy consumedby the actuators. In addition, a human-machine interface (HMI) was added to the system. With this HMI, the user can enter the set values for the room and monitor the data as a result of the measurements made by the sensors.