The majority of the DEC systems employing solid sorbent include a rotary dehumidifier. The plant’s components are installed in an air-handling unit and are activated according to the operation mode of the air-conditioning system. These operation modes implement different physical processes for air treatment, depending on the load and the outdoor air conditions. The most commonly used desiccant cooling process, works as follows (see Figures 1 and 2): The ambient air (1) is dehumidified by means of a desiccant wheel; the air temperature increases, since the process is nearly adiabatic (2). The heat recovery wheel is used to cool

the supply air by means of indirect evaporative cooling (3-4). Depending on the air inlet temperature and humidity supplied, the temperature is further reduced by direct evaporative cooling in the humidifier, with a simultaneous increase in humidity up to condition (4). The coil on the supply stream is in operation only for heating conditions. The fan releases heat, leading to an increase in the temperature of the supply air, which brings about the supply air condition (5). An increase in temperature up to 1°C is usually expected after the considered by fan.

The return air from the building is in state (6). The air is then humidified as close as possible to saturation (7). This state guarantees the maximum potential for indirect cooling of the supply air stream through the heat recovery wheel. The heat transfer process from (7) to (8) leads to an increase in the temperature of the return air stream. The air is subsequently reheated in the heating coil until it reaches state (9). The temperature of the latter is adjusted such as to guarantee the regeneration of the sorption wheel (9 to 10).