## 4 Development of Control Strategy  
A control strategy was designed to control the temperature and relative humidity of the room against disturbances, unknowns, and uncertainties. The purpose of this control is to bring the room temperature and relative humidity to the desired values quickly and to keep them constant at these values by using less energy. In order to control the temperature and humidity of the room, the temperature and humidity values of the air at the pre-cooled desiccant air cooler outlet must be adjusted. For this purpose, the speeds of the fans and desiccant wheel are adjusted by the developed control strategy for controlling temperature and relative humidity, respectively. Additionally, the water pump, which is used for supplying water into the DPCs, is controlled to switch between stop, normal operating mode, and flashing mode. Thus, the controller sends control inputs to these three actuators and arranges its operations in a way that provides maximum comfort with less energy according to system conditions and set values. The designed feedback control structure and basic scheme of the designed control strategy are shown in Figure 2. Figure 2a shows the general feedback control system structure and it consists of sensors, controllers, comparators, and processes (cooler and room). The room conditions are always measured by the temperature and relative humidity sensors during the process and the actual values of these quantities are fed back to the comparator unit to compare set (desired) values and to determine the actual error at the room conditions. These error values are sent to the controller for evaluation and control inputs are created for the actuators in the system according to the control strategy. These control inputs regulate the operating modes of the actuators to provide fast/robust room comfort and energy efficiency according to ambient conditions and system conditions. The developed control strategy is indicated in Figure 2b, clearly. In the developed control strategy, there are four main units such as a mode selection unit, fans control unit, desiccant wheel control unit, and water pump control unit. The mode selection control unit decides the operation modes of the actuators depending on the system conditions such as the ON/OFF situation of the cooler, the conditions of the atmospheric air, the errors between the actual and set values, and the condition of the water pump. After that, the mode selection unit decides the operation mode of each actuator and sends the mode selection commands to each control unit. In these units, three different operating modes have been determined for each actuator. The first modes are the OFF mode for fans and the desiccant wheel, both actuators do not work in this mode. In the second mode for the fans and desiccant wheel, the actuators are at low speeds before starting to operate the cooler in active control mode and the atmospheric air is supplied to the room by providing cooling and dehumidification. In this mode, the operation takes a short time to ensure stable air circulation so that the first air supply takes place and the cooler goes into active mode. At this stage, the atmospheric air is hotter than the room temperature, and the room temperature and relative humidity increase during this short period. After a certain time, the cooler switches to the third mode for the fans and desiccant wheel for active control of the temperature and relative humidity by adjusting the speed of these \begin{table}
\begin{tabular}{c c} \hline \hline
**Parameters** & **Value** \\ \hline Motor torque constant (K\({}_{\mathrm{t}}\)) & 0.01 N.m/Amp \\ Electromotor force constant (K\({}_{\mathrm{e}}\)) & 0.01 V/rad/sec \\ Electric inductance (L) & 0.5 H \\ Motor viscous friction constant (b) & 0.1 N.m.s \\ Moment of inertia of the rotor (J) & 0.01 kg.m\({}^{2}\) \\ Electric resistance (R) & 1 \(\Omega\) \\ \hline \hline \end{tabular}
\end{table} 
Table 1: The values of the DC motor’s parameters for fans, desiccant wheel, and water pump. actuators.